Abstract

The relationships between host factors, viral shedding, illness severity, and antibody response in respiratory syncytial virus (RSV)-induced bronchiolitis are poorly defined. These relationships were prospectively evaluated in 77 infants hospitalized with RSV bronchiolitis in multicenter, double-blind, placebo-controlled trials of RSV immunoglobulin therapy. Severity of illness was influenced by age and host risk factors but was not influenced by RSV neutralizing antibody titer or by the amount of virus in nasal secretions at enrollment. Virus recovery in nasal secretions was variable but was highest at enrollment. Viral shedding was not influenced by primary diagnosis, antibody titer, age, or duration of acute respiratory illness before enrollment. In intubated patients, the amounts of virus recovered in nasal secretions and endotracheal aspirates were highly correlated. A serum neutralizing antibody response was seen in 64% of subjects who received placebo. The response was not influenced by age, primary diagnosis, amount of virus recovered, or severity of illness but was suppressed by preexisting antibody.

Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory tract infection (LRTI) in infants and children, and RSV infections occur in predictable epidemics every year. By age 2 years, almost all children have experienced at least 1 RSV infection, and 50% have been infected ≥ 2 times [1]. Hospitalization rates are estimated to be 3% among infants < 1 year of age and are disproportionately higher among the very youngest infants, those born just before or during the RSV infection season [2–4]. Infants with congenital heart disease (CHD) or bronchopulmonary dysplasia (BPD) or who are born prematurely are at particular risk for severe bronchiolitis or pneumonia caused by RSV infection [5–8]. The clinical characteristics of illness in each of these populations have been well described elsewhere [5–8]. Other nuances of the natural history of primary RSV infection are less clear. These include the relationships of illness severity and antibody response to age, underlying condition(s), levels of maternally acquired RSV serum antibody at the time of clinical illness, and quantity of virus being shed. A better understanding of these interrelationships is important to the development of RSV vaccines and other intervention strategies against RSV illness.

We participated in placebo-controlled multicenter trials that used immunoglobulin preparations enriched for high titers of antibodies to RSV (RSVIG) (RespiGam; MedImmune) as therapy for previously healthy or high-risk infants hospitalized with RSV illness. Although, as has been reported elsewhere [9, 10], these studies did not show that RSVIG has a therapeutic benefit, they provided an opportunity to explore the interrelationship of host factors, virus replication, and antibody responses in primary RSV LRTIs.

Methods

Enrollment. Seventy-seven infants ≤2 years of age who had been hospitalized with RSV bronchiolitis at Vanderbilt University Hospital were enrolled in 2 multicenter, double-blind, placebo-controlled therapeutic trials of RSVIG (1990–1994) [9, 10]. Table 1 shows the demographic characteristics of the populations at enrollment. Of the enrolled subjects, 70% were white and 30% were black.

Table 1.

Demographic characteristics of 77 infants hospitalized at Vanderbilt University with respiratory svncvtial virus (RSV) bronchiolitis.

Table 1.

Demographic characteristics of 77 infants hospitalized at Vanderbilt University with respiratory svncvtial virus (RSV) bronchiolitis.

The first study included 33 otherwise healthy infants (18 of whom received placebo and 15 of whom received RSVIG) with RSV LRTIs. Subjects had exhibited symptoms of acute LRTI for ≤4 days and had initial respiratory illness scores > 2.5 (twice daily scoring of illness severity was done as described elsewhere [9]). The second study included 44 infants (22 of whom received placebo and 22 of whom received RSVIG) who were at higher risk for severe LRTI with RSV disease [10]. Infants in the high-risk study had received a diagnosis of CHD or BPD or had been born prematurely (at < 32 weeks of gestation). “CHD” was defined as the presence of a cardiac anomaly either with pulmonary hypertension or requiring chronic digitalis and/or diuretic therapy. We defined “BPD” as the need for supplemental oxygen within 6 months of study enrollment in infants born at < 35 weeks of gestation who required mechanical ventilation in the neonatal period and subsequent supplemental oxygen for > 1 month. Subjects had exhibited acute LRTI symptoms for ≤4 days and had received an initial respiratory illness score of > 1.0. For purposes of analysis, a primary diagnosis of CHD was assigned to infants who had CHD and ≥ 1 other high-risk condition. In infants without CHD, BPD, if present, was the primary diagnosis assigned. Prematurity (PM) was the risk factor assigned to infants who had neither CHD nor BPD (see table 1 for details).

Exclusion criteria for both studies included any previously diagnosed immunodeficiency, cystic fibrosis, reactive airways disease or asthma, poorly controlled congestive heart failure before the current hospital admission, renal failure, ventilator dependency at the time of enrollment, life expectancy < 6 months, apnea without evidence of LRTI, previous reaction to blood products, receipt of immunoglobulin therapy in the preceding 2 months, enrollment in an intravenous RSV prophylaxis protocol; or receipt of ribavirin treatment in the preceding month.

Detection of RSV antigen in nasal washings (NWs) by ELISA (Testpak; Abbott) was required for enrollment, and subsequent confirmation of RSV infection by viral culture was required for continuation in the study.

Study design-clinical. Enrolled subjects were randomly assigned in a double-blind fashion at a ratio of 1:1 to receive intravenous RSVIG (MedImmune) or albumin placebo. Enrollment and follow-up of subjects was performed according to the overall study design of these multicenter trials [9, 10]. While hospitalized, infants were evaluated twice daily to establish a respiratory illness score, and daily NWs (and endotracheal tube [ET] aspirates, for intubated patients) were obtained for use in quantitative viral cultures. Serum samples and NWs were obtained at enrollment, at 24 h after enrollment, and at 8 weeks after enrollment for analysis of immune responses, per the study protocol. Supplemental studies of viral shedding and serologic response were performed at the Vanderbilt site as described below; for these studies, additional serum samples were collected before and after the subsequent RSV infection season.

Interventions related to patient care (e.g., use of bronchodilators, supplemental oxygen, ventilatory support, and ribavirin) and decisions regarding discharge were left to the discretion of each patient's primary care physician. Outcome measures of illness severity included the sum of the respiratory illness scores for up to 13 days after enrollment, length of time in which supplemental oxygen was required, and length of time in which ventilatory support was needed.

A subset of 42 patients were evaluated at the start of the subsequent RSV season, and 34 of these patients were followed up through the season for serologic evidence of duration of immunity, reinfection, and rehospitalization. No attempt was made to isolate RSV a second time from patients who became ill.

Study design—laboratory. RSV isolation and identification were done as described elsewhere [9]. Titers in specimens were measured immediately on collection, without prior freezing. Available isolates from all 4 RSV seasons were identified as subgroup A or B viruses by immunofluorescence, using group-specific monoclonal antibodies (MAbs) 92–11C and 102–1013 (courtesy of L. Anderson, Centers for Disease Control and Prevention, Atlanta). MAbs were used at a 1:4000 dilution in PBS cell scrapings from HEp-2 cells infected with the RSV isolate that was to be tested. Goat anti-mouse IgG antibody (Bartels) and then Evans blue counterstain were applied, and immunofluorescent cells were identified. No attempt was made to characterize viruses by strain variation.

Measurement of RSV was done with fresh NWs and ET specimens by plaque assay and reported as plaque-forming units per milliliter, as described elsewhere [11]. Serum neutralizing antibody titers were determined by a 60% plaque-reduction neutralization assay [11]. The starting dilution for serum antibody determinations was 1: 20. Antibody responses are reported only for placebo recipients. Antibody titers at 8 weeks were corrected for decay from the time of infection (estimated half-life, 21 days) of passively acquired maternal antibody in infants < 6 months old. A ≥4-fold increase in corrected serum antibody levels or seroconversion from negative to positive for RSV at 8 weeks after enrollment was considered to be evidence of antibody response to infection.

IgA and IgG antibody responses in serum and NWs to RSV F and GA proteins (courtesy of E. Walsh, University of Rochester, Rochester, NY, and Wyeth Lederle Vaccines) were determined by a kinetic ELISA previously developed for influenza and adapted to detection of antibodies to the F and GA proteins [12]. The dilutions used were 1:20 for serum antibody determinations and 1:4 for NW antibody determinations. A kinetic ELISA value > 5 milli-optical destiny/min was considered to be evidence of the presence of specific antibody. Total IgA was determined to ensure that the specimens had measurable IgA, but the values were not corrected for total IgA. Data for these ELISA determinations are more fragmentary than neutralization results because of a lack of sample availability.

Statistical analysis. Descriptive and exploratory graphical analyses were used to investigate the distribution of demographic characteristics and to identify outlying data. Two children > 600 days old were excluded from the analysis of age influence. We used χ2 or Fisher's exact tests, as appropriate, for contingency table analyses. The mean amount of virus recovered from NWs over time was analyzed by 1-way analysis of variance (ANOVA). Univariate comparisons of continuous variables were made with a t test and a nonparametric Mann-Whitney test. Results were consistent, and we reportthe P values fort tests (P < .05 was considered significant).We compared relationships by using Pearson's correlation and scatterplot. Best-fit regression analysis was used to determine the best models for illness severity. Analysis was done by using SPSS Interactive Graphics for Windows, version 10.0.5, and SAS for Windows (SAS Institute), version 8.0.

Results

Factors influencing illness severity. Severity of illness at study entry could not be analyzed in terms of risk status, because the severity-of-illness entry criteria for the study involving otherwise healthy infants and the high-risk study differed. Although the illness criterion for admission to the low-risk trial included a severity score ≥2.5 on entry, the traditional high-risk groups of BPD and CHD were each identified by ≥1 independent criteria as having a more-severe course of illness (table 2). CHD had the strongest association with severe illness, as has been reported elsewhere [3, 8]. The younger a child was when acquisition of RSV occurred, the more severe was the course of illness during hospitalization, by several criteria (table 2). However, the severity of illness, as judged by total illness score, had no correlation with serum neutralizing antibody titer at enrollment (figure IA) or titer of RSV in NWs (figure 1B).

Table 2.

Relationship between respiratory illness severity and host factors in 77 children hospitalized at Vanderbilt University with respiratory syncytial virus bronchiolitis.

Table 2.

Relationship between respiratory illness severity and host factors in 77 children hospitalized at Vanderbilt University with respiratory syncytial virus bronchiolitis.

Figure 1.

Relationships between total illness score (sum of twice daily scoring on a 1–5 scale [9], in which 5 is the most severe [e.g., requiring intubation]), serum neutralizing antibody titer (A), and quantity of respiratory syncytial virus (RSV) recovered from nasal secretions (B) at enrollment. Illness was scored during hospitalization for up to 13 days.

Figure 1.

Relationships between total illness score (sum of twice daily scoring on a 1–5 scale [9], in which 5 is the most severe [e.g., requiring intubation]), serum neutralizing antibody titer (A), and quantity of respiratory syncytial virus (RSV) recovered from nasal secretions (B) at enrollment. Illness was scored during hospitalization for up to 13 days.

RSV isolates could be retrieved for serotyping into subgroups A and B from only 21 subjects; 16 (76%) of 21 virus isolates were of group A, and 5 (24%) were of group B. Too few isolates were available for severity of illness to be analyzed by strain, although RSV A strains are reported to cause more-severe illness [13].

Factors influencing viral shedding. The quantity of RSV recovered from NWs at trial entry was not influenced by serum antibody titer (figure 2A) and did not vary by age (figure 2B). Within 48 h of trial entry, the mean amount of virus recovered from the NWs of patients receiving RSVIG and patients receiving placebo was 10-fold lower than entry levels (figure 3), a significant difference, by ANOVA, for both placebo (P = .017) and RSVIG (P = .015) groups. We compared the quantity of RSV shed in NWs and ET aspirates in a subset of 16 intubated patients. In this group, NW RSV titers were highly variable but strongly correlated with ET titers in individual patients (figure 4; P < .001).

Figure 2.

Relationships between quantity of respiratory syncytial virus (RSV) recovered, serum neutralizing antibody titer (A), and age in days (B) at enrollment. No significant interactions between these variables were seen.

Figure 2.

Relationships between quantity of respiratory syncytial virus (RSV) recovered, serum neutralizing antibody titer (A), and age in days (B) at enrollment. No significant interactions between these variables were seen.

Figure 3.

The quantity of respiratory syncytial virus (RSV) recovered from nasal secretions decreased significantly after enrollment in both placebo (○) and RSV immunoglobulin (RSVIG; Δ) groups. A significant decrease, by 1-way analysis of variance, was seen in the mean level between 0 and 1 and between 1 and 2 days after enrollment in both groups.

Figure 3.

The quantity of respiratory syncytial virus (RSV) recovered from nasal secretions decreased significantly after enrollment in both placebo (○) and RSV immunoglobulin (RSVIG; Δ) groups. A significant decrease, by 1-way analysis of variance, was seen in the mean level between 0 and 1 and between 1 and 2 days after enrollment in both groups.

Figure 4.

Equivalent amounts of respiratory syncytial virus (RSV) were recovered from nasal and endotracheal secretions. The amounts of virus shed by an infant in these 2 sites were highly correlated (R = 0.80; P < .001).

Figure 4.

Equivalent amounts of respiratory syncytial virus (RSV) were recovered from nasal and endotracheal secretions. The amounts of virus shed by an infant in these 2 sites were highly correlated (R = 0.80; P < .001).

Factors influencing enrollment antibody titers. Antibody titers at enrollment were lower, although not significantly so, in the BPD and PM groups, in which patients might have been expected to have less transplacental antibody (figure 5A). Antibody titers at entry were inversely correlated with age, as would be expected, since younger children have relatively higher levels of residual maternal antibody (figure 5B). At entry, 64% of the infants were seronegative. At 24 h after entry, a difference in neutralizing titers was seen between placebo and RSVIG groups, and the expected rise in titers among the RSVIG recipients occurred, to a mean titer of 1:1000. However, no changes in neutralizing antibody titers were seen in the placebo group at 24 h after enrollment—indicating that this arm of the immune defense was not yet operational—and there was no evidence of consumption of antibody through binding to antigen.

Figure 5.

Relationships between respiratory syncytial virus neutralizing antibody titer, primary diagnosis (A), and age (B) at enrollment. Neutralizing antibody titer at admission was significantly positively correlated with age (P = .027). In panel A, a number of overlapping points appear at the seronegative log24.4 value. BPD, bronchopulmonary dysplasia; CHD, chronic heart disease; PM, prematurity. Dashed line, minimum detectable antibody level.

Figure 5.

Relationships between respiratory syncytial virus neutralizing antibody titer, primary diagnosis (A), and age (B) at enrollment. Neutralizing antibody titer at admission was significantly positively correlated with age (P = .027). In panel A, a number of overlapping points appear at the seronegative log24.4 value. BPD, bronchopulmonary dysplasia; CHD, chronic heart disease; PM, prematurity. Dashed line, minimum detectable antibody level.

Evaluation of antibody response to infection. The increase in antibody levels at 8 weeks could only be assessed in the placebo group. Of 33 infants in the placebo group, 21 (64%) had an increase in neutralizing antibody titers. Numbers were too small to make any correlations with risk groups. The responses were not influenced by titer of virus at enrollment, severity of illness, or age. The presence of maternally derived neutralizing antibody in the enrollment sample was associated with fewer antibody responses: only 2 (25%) of 8 seropositive children made a response in whom preexisting antibody was present, compared with 19 (76%) of 25 seronegative children (P = .015). The number of children with neutralizing antibody responses was not smaller among the 17 children < 90 days of age at trial enrollment than among the 16 children >90 days of age (65% vs. 63%, respectively).

Table 3 shows the numbers of placebo recipients with serum and mucosal IgA and IgG neutralizing antibodies to F and G proteins. No single response exceeded the seroconversion rate seen with neutralizing antibodies. The frequency of increases in IgG antibody to F protein was significantly diminished by the presence of neutralizing antibody (P = .028), but this comparison was not statistically significant when the analysis was controlled for age. Increases in the levels of IgG antibody to GA protein were not significantly diminished in association with age in days or preexisting maternal antibody. One-third of placebo recipients had mucosal IgA responses. Mucosal responses were not influenced by age or preexisting neutralizing antibody. By the subsequent autumn, 6–8 months after vaccination, more than two-thirds of available subjects were seronegative, and one-half were reinfected in the subsequent RSV season. None were rehospitalized

Table 3.

Serum and mucosal antibody responses in placebo recipients 8 weeks after enrollment in a study in infants hospitalized with respiratory syncytial virus bronchiolitis.

Table 3.

Serum and mucosal antibody responses in placebo recipients 8 weeks after enrollment in a study in infants hospitalized with respiratory syncytial virus bronchiolitis.

Discussion

RSV has been the major cause of LRTIs in infants since its recognition >40 years ago. Unfortunately, progress in our understanding of the epidemiology of RSV has not been matched by concomitant development of effective intervention strategies. The use of inactivated RSV vaccines in the 1960s led to exaggerated illness after subsequent natural RSV infection [14–16]; the live vaccines of the 1970s lacked infectivity or were insufficiently attenuated [17–19]; and the effectiveness of ribavirin in treating infection was found to be limited [20]. Monthly prophylaxis with RSV polyclonal and monoclonal gamma globulin preparations against RSV illness is effective in children with BPD [21–23], but it is too costly and inconvenient to be used in otherwise healthy children.

We analyzed data from RSVIG treatment trials to better define the factors associated with increased severity of disease and to identify factors associated with development of a protective immune response. These results will help guide future prevention and intervention strategies.

The lack of a relationship between viral shedding and clinical outcome has been noted [24]. In our study, the virus titer at enrollment was highly variable and in no way predictive of severity of illness at admission or of the course of illness. The amount of virus shed by some children was impressively high (107 pfu/mL was not uncommon) when titers of virus in nasal samples were directly measured. The highest virus titers were seen at enrollment and decreased within 48 h of admission. Children in whom virus burden begins to decrease shortly after the onset of an LRTI likely are late in the course of the viral infection. Analogously, children receiving live attenuated RSV vaccines have peak viral shedding on days 6–8 after vaccine administration, and the decline in titer begins on day 9 [25]. Thus, further reduction in virus titer alone may be relatively insignificant in affecting outcome. These observations are consistent with the limited or absent clinical effectiveness of treatment strategies directed at reduction of virus load (e.g., administration of ribavirin or RSVIG) in children hospitalized with RSV bronchiolitis [9, 10, 21]. At the postulated time of peak illness, 8–10 days after infection, inflammatory and immune-mediated processes set in motion by the infection may play an important role in determining illness severity. However, neither broad immunosuppression resulting from use of steroids nor bronchodilators have been shown to have any benefit in improving the outcome for children hospitalized with bronchiolitis [26–29].

In intubated children, a subset of our study groups, a close correlation was seen between the amount of virus being shed in the lungs and the amount shed in the nasal passages. Thus, there is no dissociation between viral replication at these 2 respiratory tract sites. Again, even in infants sick enough to require intubation, virus loads were highly variable and were not, on average, higher than the virus loads seen in less ill patients.

A number of factors were associated with more-severe disease after hospitalization. PM and CHD increased the likelihood of more-severe disease (as defined by clinical scoring, duration of supplemental oxygen, and/or need for ventilatory support). Age in days was inversely correlated with duration of supplemental oxygen and need for ventilatory support. These observations support findings of similar, smaller studies [5–7,30,31]. Large-scale studies in Canada and Tennessee have further defined the relative importance of host risk factors in determining whether RSV infection leads to hospitalization [3, 32, 33]. In our study, we saw greater severity of RSV infection in children with BPD or CHD, even though the criteria for study enrollment in high-risk groups were less stringent than those for healthy groups.

Inconsistent and poorly sustained systemic and mucosal immune responses to RSV (F and GA proteins and neutralizing antibody) were observed in our population of children with bronchiolitis. Other investigators have noted poor responses to specific RSV proteins and diminished immunoglobulin class and subclass responses after primary infection in children < 1 year of age [34–39]. Neutralizing antibody to RSV is observed less commonly than antibody to specific proteins in young children [40, 41]. Brandenburg et al. [34] reported poor neutralizing antibody responses to RSV infection in infants < 6 months old. No correlation was found between parameters of illness severity and antibody response, although details of RSV illness severity were not provided.

In our population of children with RSV bronchiolitis, onethird of placebo recipients had not mounted an antibody response to RSV, as determined by measurement of serum neutralizing antibody, by 8 weeks after infection, and two-thirds of both placebo and RSVIG recipients had no residual antibody 6 months later. Serologic responses were not related to the quantity of RSV shedding or to illness severity in these children. IgG responses to the F protein were diminished in the presence of maternally derived antibody, but this association could not be distinguished from the association with age by multivariate analysis. This is somewhat discrepant with a previous observation suggesting that response to F protein was influenced primarily by age and to G protein by preexisting antibody [41]. Age and preexisting antibody of maternal origin are closely interrelated at the age at which most children have a first RSV infection. One-half of the infants followed up in our studies, whether they received RSVIG or not, were reinfected in the subsequent RSV season, as determined by a 4-fold rise in antibody titers, but none were rehospitalized.

Recent vaccine trial data suggest that the most consistent immune response to a live attenuated intranasal vaccine and the best correlate of immunity on rechallenge with vaccine is a serum IgA response to the G protein [42]. In this study, the IgA response to G protein was not as striking. The variation in G protein between group A and group B RSV might account for some of the discrepancy. The serum and mucosal IgA responses seen in this study were not influenced by age or by the presence of maternal antibody, which suggests that there may be a selective response in young children, as was seen in the vaccine trial [42]. In contrast, in some studies, younger infants failed to develop detectable NW secretory antibody to RSV infection more frequently than did older infants [43].

Although the neutralizing antibody assays were not performed in parallel, children who experienced natural infection leading to hospitalization were more likely to be seronegative for RSV on presentation (47%) than were healthy children of a similar age (24%) who participated in vaccine trials [42], which suggests that susceptibility to serious illness is based on seronegativity, as reported by Glezen et al. [44].

The failure of some seronegative hospitalized infants to adequately mount and sustain a serum RSV neutralizing antibody response, particularly in the presence of maternally derived antibody, implies that there may be a formidable barrier to effective immunization of young infants against RSV infection. This observation may apply to immune responses to live viral mucosal vaccines in general, even though RSV and other respiratory viruses acquired through vaccination or natural infection replicate well in the mucosa, with no interference from serum antibody. Infants < 6 months of age demonstrate reduced serologic responses to live attenuated influenza virus and to rotavirus, in comparison with older children [45, 46].

Serum neutralizing antibody plays a role in protecting an infant against severe RSV infection. The observations of Glezen et al. [44] and passive immunoprophylaxis studies in humans [21–23] show that a serum neutralizing antibody titer of 1:300 is sufficient to protect young infants against being hospitalized with RSV illness. However, alternative immune mechanisms may be important in preventing RSV illness. A local mucosal antibody response may be sufficient to block cellular entry or intracellular replication of RSV [47, 48], and an early cytotoxic T cell response might favorably influence the course of infection, as is suggested by murine models in which cytotoxic T cells and T helper subsets are important to virus clearance [49] and in which manipulation of the cytokine environment can have an impact on the efficiency of virus clearance, type of pathology, and magnitude of illness [50].

Successful immunization against RSV will require a full understanding of the ontogeny of immune response to respiratory virus antigens in very young children and continued definition of correlates of protection against disease. The lack of correlation between severity of natural infection with RSV in infancy and the amount of virus present or the level of neutralizing antibody in the serum reinforces the need to explore the hypothesis that natural infection with RSV is an immune-modulated disease.

Acknowledgments

We acknowledge the assistance of Penny Satterwhite, Lori Steele, and Peggy Bender, in patient recruitment and evaluation; Melody Mestemacher, for data entry; and Mine lkizler, for assistance with figure preparation.

References

1.
Frank
AL
Kasel
JA
Risk of primary infection and reinfection with respiratory syncytial virus
Am J Dis Child
 , 
1986
, vol. 
140
 (pg. 
543
-
6
)
2.
Fisher
R
Gruber
W
Edwards
KM
, et al.  . 
Twenty years of outpatient respiratory syncytial virus infection: a framework for vaccine efficacy trials
Pediatrics [serial online]
 , 
1997
, vol. 
99
 pg. 
e7
  
3.
Boyce
TG
Mellen
BG
Mitchel
EF
Jr
Wright
PF
Griffin
MR
Rates of hospitalization for respiratory syncytial virus infection among children in medicaid
J Pediatr
 , 
2000
, vol. 
137
 (pg. 
865
-
70
)
4.
Shay
DK
Holman
RC
Newman
RD
Liu
LL
Stout
JW
Anderson
LJ
Bronchiolitis-associated hospitalizations among US children, 1980–1996
JAMA
 , 
1999
, vol. 
282
 (pg. 
1440
-
6
)
5.
Tammela
OK
First-year infections after initial hospitalization in low birth weight infants with and without bronchopulmonary dysplasia
Scand J Infect Dis
 , 
1992
, vol. 
24
 (pg. 
515
-
24
)
6.
Meert
K
Heidemann
S
Lieh-Lai
M
Sarnaik
AP
Clinical characteristics of respiratory syncytial virus infections in healthy versus previously compromised host
Pediatr Pulmonol
 , 
1989
, vol. 
7
 (pg. 
167
-
70
)
7.
Groothuis
JR
Gutierrez
KM
Lauer
BA
Respiratory syncytial virus infection in children with bronchopulmonary dysplasia
Pediatrics
 , 
1988
, vol. 
82
 (pg. 
199
-
203
)
8.
MacDonald
NE
Hall
CB
Suffin
SC
Alexson
C
Harris
PJ
Manning
JA
Respiratory syncytial viral infection in infants with congenital heart disease
N Engl J Med
 , 
1982
, vol. 
307
 (pg. 
397
-
400
)
9.
Rodriguez
WJ
Gruber
WC
Groothuis
JR
, et al.  . 
Respiratory syncytial virus immune globulin treatment of RSV lower respiratory tract infections in previously healthy children
Pediatrics
 , 
1997
, vol. 
100
 (pg. 
937
-
42
)
10.
Rodriguez
WJ
Gruber
WC
Welliver
RC
, et al.  . 
Respiratory syncytial virus (RSV) immune globulin intravenous therapy for RSV lower respiratory tract infection in infants and young children at high risk for sever RSV infections. Respiratory Syncytial Virus Immune Globulin Study Group
Pediatrics
 , 
1997
, vol. 
99
 (pg. 
454
-
61
)
11.
Graham
BS
Perkins
MD
Wright
PF
Karzon
DT
Primary respiratory syncytial virus infection in mice
J Med Virol
 , 
1988
, vol. 
26
 (pg. 
153
-
62
)
12.
Boyce
TG
Gruber
WC
Coleman-Dockery
SD
, et al.  . 
Mucosal immune response to trivalent live attenuated intranasal influenza vaccine in children
Vaccine
 , 
1999
, vol. 
18
 (pg. 
82
-
8
)
13.
McConnochie
KM
Hall
CB
Walsh
EE
Roghmann
KJ
Variation in severity of respiratory syncytial virus infections with subtype
J Pediatr
 , 
1990
, vol. 
117
 (pg. 
52
-
62
)
14.
Chin
J
Magoffin
RL
Shearer
LA
Schieble
JH
Lennette
EH
Field evaluation of a respiratory syncytial virus vaccine and a trivalent parainfluenza virus vaccine in a pediatric population
Am J Epidemiol
 , 
1969
, vol. 
89
 (pg. 
449
-
63
)
15.
Kapikian
AZ
Mitchell
RH
Chanock
RM
Shvedoff
RA
Stewart
CE
An epidemiologic study of altered clinical reactivity to respiratory syncytial (RS) virus infection in children previously vaccinated with an inactivated RS virus vaccine
Am J Epidemiol
 , 
1969
, vol. 
89
 (pg. 
405
-
21
)
16.
Kim
HW
Canchola
JG
Brandt
CD
, et al.  . 
Respiratory syncytial virus disease in infants despite prior administration of antigenic inactivated vaccine
Am J Epidemiol
 , 
1969
, vol. 
89
 (pg. 
422
-
34
)
17.
McKay
E
Higgins
P
Tyrrell
D
Pringle
C
Immunogenicity and pathogenicity of temperature-sensitive modified respiratory syncytial virus in adult volunteers
J Med Virol
 , 
1988
, vol. 
25
 (pg. 
411
-
21
)
18.
Wright
PF
Shinozaki
T
Fleet
W
Sell
SH
Thompson
J
Karzon
DT
Evaluation of a live, attenuated respiratory syncytial virus vaccine in infants
J Pediatr
 , 
1976
, vol. 
88
 (pg. 
931
-
6
)
19.
Wright
PF
Belshe
RB
Kim
HW
Van Voris
LP
Chanock
RM
Administration of a highly attenuated, live respiratory syncytial virus vaccine to adults and children
Infect Immun
 , 
1982
, vol. 
37
 (pg. 
397
-
400
)
20.
Reassessment of the indications for ribavirin therapy in respiratory syncytial virus infections. American Academy of Pediatrics Committee on Infectious Diseases
Pediatrics
 , 
1996
, vol. 
97
 (pg. 
137
-
40
)
21.
Groothuis
JR
Levin
MJ
Rodriguez
W
, et al.  . 
Use of intravenous gamma globulin to passively immunize high-risk children against respiratory syncytial virus: safety and phannacokinetics. The RSVIG Study Group
Antimicrob Agents Chemother
 , 
1991
, vol. 
35
 (pg. 
1469
-
73
)
22.
Groothuis
JR
Simoes
AF
Levin
ML
, et al.  . 
Prophylactic virus immune globulin to high-risk infants and young children
N Engl J Med
 , 
1993
, vol. 
329
 (pg. 
1524
-
30
)
23.
Reduction of respiratory syncytial virus hospitalization among premature infants and infants with bronchopulmonary dysplasia using respiratory syncytial virus immune globulin prophylaxis. The PREVENT Study Group
Pediatrics
 , 
1997
, vol. 
99
 (pg. 
93
-
9
)
24.
Hall
CB
Douglas
RG
Jr
Geiman
JM
Quantitative shedding patterns of respiratory syncytial virus in infants
J Infect Dis
 , 
1975
, vol. 
132
 (pg. 
151
-
6
)
25.
Kim
HW
Arrobio
JO
Pyles
G
, et al.  . 
Clinical and immunological response of infants and children to administration of low-temperature adapted respiratory syncytial virus
Pediatrics
 , 
1971
, vol. 
48
 (pg. 
745
-
55
)
26.
Leer
JA
Jr
Green
JL
Heimlich
EM
, et al.  . 
Corticosteroid treatment in bronchiolitis: a controlled, collaborative study in 297 infants and children
Am J Dis Child
 , 
1969
, vol. 
117
 (pg. 
495
-
503
)
27.
Dabbous
IA
Tkachyk
IS
Stamm
SJ
A double blind study on the effects of corticosteroids in the treatment of bronchiolitis
Pediatrics
 , 
1966
, vol. 
37
 (pg. 
477
-
84
)
28.
Roosevelt
G
Sheehan
K
Group-Phelan
J
Tanz
RR
Listernick
R
Dexamethasone in bronchiolitis: a randomised controlled trial
Lancet
 , 
1996
, vol. 
348
 (pg. 
292
-
5
)
29.
Klassen
TP
Sutcliffe
T
Watters
LK
Wells
GA
Allen
UD
Li
MM
Dexamethasone in salbutamol-treated inpatients with acute bronchiolitis: a randomized, controlled trial
J Pediatr
 , 
1997
, vol. 
130
 (pg. 
191
-
6
)
30.
Simoes
EA
King
SJ
Lehr
MV
Groothuis
JR
Preterm twins and triplets: a high-risk group for severe respiratory syncytial virus infection
Am J Dis Child
 , 
1993
, vol. 
147
 (pg. 
303
-
6
)
31.
Moler
FW
Khan
AS
Meliones
IN
Custer
JR
Palmisano
J
Shope
TC
Respiratory syncytial virus morbidity and mortality estimates in congenital heart disease patients: a recent experience
Crit Care Med
 , 
1992
, vol. 
20
 (pg. 
1406
-
13
)
32.
Wang
EE
Law
BJ
Stephens
D
Pediatric Investigators Collaborative Network on Infections in Canada (PICNIC) prospective study of risk factors and outcomes in patients hospitalized with respiratory syncytial viral lower respiratory tract infection
J Pediatr
 , 
1995
, vol. 
126
 (pg. 
212
-
9
)
33.
Navas
L
Wang
E
de Carvalho
V
Robinson
J
Improved outcome of respiratory syncytial virus infection in a high-risk hospitalized population of Canadian children. Pediatric Investigators Collaborative Network on Infections in Canada
J Pediatr
 , 
1992
, vol. 
121
 (pg. 
348
-
54
)
34.
Brandenburg
AH
Green
J
van Steensel-Moll
HA
, et al.  . 
Respiratory syncytial virus specific serum antibodies in infants under six months of age: limited serologic response upon infection
J Med Virol
 , 
1997
, vol. 
52
 (pg. 
97
-
104
)
35.
Ward
KA
Lambden
PR
Ogilvie
MM
Watt
PJ
Antibodies to respiratory syncytial virus polypeptides and their significance in human infection
J Gen Virol
 , 
1983
, vol. 
64
 (pg. 
1867
-
76
)
36.
Watt
PJ
Zardis
M
Lambden
PR
Age related IgG subclass response to respiratory syncytial virus fusion protein in infected infants
Clin Exp Immunol
 , 
1986
, vol. 
64
 (pg. 
503
-
9
)
37.
Wagner
DK
Muelenaer
P
Henderson
FW
, et al.  . 
Serum immunoglobulin G antibody subclass response to respiratory syncytial virus F and G glycoproteins after first, second, and third infections
J Clin Microbiol
 , 
1989
, vol. 
27
 (pg. 
589
-
92
)
38.
Popow-Kraupp
T
Lakits
E
Kellner
G
Kunz
C
Immunoglobulin-classspecific immune response to respiratory syncytial virus structural proteins in infants, children, and adults
J Med Virol
 , 
1989
, vol. 
27
 (pg. 
215
-
23
)
39.
Welliver
RC
Kaul
TN
Putnam
TI
Sun
M
Riddlesberger
K
Ogra
PL
The antibody response to primary and secondary infection with respiratory syncytial virus: kinetics of class-specific responses
J Pediatr
 , 
1980
, vol. 
96
 (pg. 
808
-
13
)
40.
Richardson
LS
Yolken
RH
Belshe
RB
Camargo
E
Kim
HW
Chanock
RM
Enzyme-linked immunosorbent assay for measurement of serological response to respiratory syncytial virus infection
Infect Immun
 , 
1978
, vol. 
20
 (pg. 
660
-
4
)
41.
Murphy
BR
Graham
BS
Prince
GA
, et al.  . 
Serum and nasal-wash immunoglobulin G and A antibody response of infants and children to respiratory syncytial virus F and G glycoproteins following primary infection
J Clin Microbiol
 , 
1986
, vol. 
23
 (pg. 
1009
-
14
)
42.
Wright
PF
Karron
RA
Belshe
RB
, et al.  . 
Evaluation of a live, cold-passaged, temperature-sensitive, respiratory syncytial virus vaccine in infancy
J Infect Dis
 , 
2000
, vol. 
182
 (pg. 
1331
-
42
)
43.
Parrott
RH
Kim
HW
Arrobio
JO
, et al.  . 
Epidemiology of respiratory syncytial virus infection in Washington, DC. II. Infection and disease with respect to age, immunologic status, race and sex
Am J Epidemiol
 , 
1973
, vol. 
98
 (pg. 
289
-
300
)
44.
Glezen
WP
Paredes
A
Allison
JE
Taber
LH
Frank
AL
Risk of respiratory syncytial virus infection for infants from low-income families in relationship to age, sex, ethnic group, and maternal antibody level
J Pediatr
 , 
1981
, vol. 
98
 (pg. 
708
-
15
)
45.
Gruber
WC
Darden
PM
Still
JG
Lohr
J
Reed
G
Wright
PF
Evaluation of bivalent live attenuated influenza A vaccines in children 2 months to 3 years of age: safety, immunogenicity and dose-response
Vaccine
 , 
1997
, vol. 
15
 (pg. 
1379
-
84
)
46.
Kobayashi
M
Thompson
J
Tollefson
SJ
Reed
GW
Wright
PF
Tetravalent rhesus rotavirus vaccine in young infants
J Infect Dis
 , 
1994
, vol. 
170
 (pg. 
1260
-
3
)
47.
McIntosh
K
Masters
HB
Orr
I
Chao
RK
Barkin
RM
The immunologic response to infection with respiratory syncytial virus in infants
J Infect Dis
 , 
1978
, vol. 
138
 (pg. 
24
-
32
)
48.
Kaul
TN
Welliver
RC
Wong
DT
Udwadia
RA
Riddlesberger
K
Ogra
PL
Secretory antibody response to respiratory syncytial virus infection
Am J Dis Child
 , 
1981
, vol. 
135
 (pg. 
1013
-
6
)
49.
Graham
BS
Bunton
LA
Wright
PF
Karzon
DT
Role of T lymphocyte subsets in the pathogenesis of primary infection and rechallenge with respiratory syncytial virus in mice
J Clin Invest
 , 
1991
, vol. 
88
 (pg. 
1026
-
33
)
50.
Graham
BS
Pathogenesis of respiratory syncytial virus vaccine-augmented pathology [review]
Am J Respir Crit Care Med
 , 
1995
, vol. 
152
 
Suppl 4
(pg. 
S63
-
6
)

Author notes

Presented in part: RSV after 45 Years, International Society for Antiviral Research, Segovia, Spain, October 2001.
Informed consent was obtained from parents or guardians of study subjects, and the human experimentation guidelines of the US Department of Health and Human Services and of Vanderbilt University were followed in conducting the clinical research. The Vanderbilt Institutional Review Board approved the studies.
Financial support: MedImmune (clinical phase of investigation); National Institutes of Health (AI-65298).
a
Present affiliations: Wyeth Lederle Vaccines, Pearl River, New York (W.C.G.); University of Massachusetts, Worchester (G.R.); Vaccine Research Center, National Institutes of Health, Bethesda, Maryland (B.S.G.).