Antibody Response After the Third SARS-CoV-2 Vaccine in Solid Organ Transplant Recipients and People Living With HIV (COVERALL-2)

Abstract Background After basic immunization with 2 mRNA SARS-CoV-2 vaccine doses, only a small proportion of patients who are severely immunocompromised generate a sufficient antibody response. Hence, we assessed the additional benefit of a third SARS-CoV-2 vaccine in patients with different levels of immunosuppression. Methods In this observational extension of the COVERALL trial (Corona Vaccine Trial Platform), we recruited patients from the Swiss HIV Cohort Study and the Swiss Transplant Cohort Study (ie, lung and kidney transplant recipients). We collected blood samples before and 8 weeks after the third SARS-CoV-2 vaccination with either mRNA-1273 (Moderna) or BNT162b2 (Pfizer-BioNTech). The primary outcome was the proportion of participants showing an antibody response (Elecsys Anti-SARS-CoV-2 S test; threshold ≥100 U/mL) 8 weeks after the third SARS-CoV-2 vaccination. We also compared the proportion of patients who reached the primary outcome from basic immunization (the first and second vaccines) to the third vaccination. Results Nearly all participants (97.2% [95% CI, 95.9%–98.6%], 564/580) had an antibody response. This response was comparable between mRNA-1273 (96.1% [95% CI, 93.7%–98.6%], 245/255) and BNT162b2 (98.2% [95% CI, 96.7%–99.6%], 319/325). Stratification by cohort showed that 99.8% (502/503) of people living with HIV and 80.5% (62/77) of recipients of solid organ transplants achieved the primary endpoint. The proportion of patients with an antibody response in solid organ transplant recipients improved from the second vaccination (22.7%, 15/66) to the third (80.5%, 62/77). Conclusions People living with HIV had a high antibody response. The third vaccine increased the proportion of solid organ transplant recipients with an antibody response. Clinical Trials Registration. NCT04805125 (ClinicalTrials.gov).

SARS-CoV-2 emerged late in 2019 in Wuhan, China, and induced a pandemic [1][2][3].Approximately 1 year later, SARS-CoV-2 vaccines became available and were tested in large randomized placebo-controlled trials and determined safe and effective in terms of preventing COVID-19 [4,5].However, while the efficacy of vaccines was tested thoroughly in the general population, there was little evidence on vaccine protection in more vulnerable groups, such as patients who are immunocompromised [6].Consequently, the Corona Vaccine Trial Platform (COVERALL) was established [7,8].COVERALL is a platform trial nested into the Swiss HIV Cohort Study (SHCS) [9] and the Swiss Transplant Cohort Study (STCS) [7,10].

Open Forum Infectious Diseases
for patients who were immunocompromised [11].While nearly all people living with HIV (PLWH) had an antibody response after 2 doses (Elecsys Anti-SARS-CoV-2 S test; threshold ≥100 U/mL), this was the case for only 24% of solid organ transplant (SOT) recipients.Previous evidence suggests that SOT recipients may benefit from a third vaccine [6,14].In late 2021, a third SARS-CoV-2 vaccine dose was recommended by Swiss health authorities to improve the protection of patients, as well as to account for genetic drift and emergence of new variants [13].
Hence, we initiated a new substudy to the COVERALL platform (COVERALL-2) in which we aimed to assess the benefit and potential harm of a third SARS-CoV-2 vaccine for patients who were immunocompromised among those recruited from the SHCS and the STCS.This observational study allowed for the inclusion of additional patients beyond the original randomized trial population (COVERALL-1).

Study Oversight and Participants
The COVERALL platform study consists of 1 master protocol and 2 subprotocols.All protocols were approved by the ethical committee Nordwest-and Zentralschweiz, Switzerland (BASEC 2021-000593), and the full protocols are publicly available on trial registry (https://clinicaltrials.gov/ct2/show/NCT04805125).
This observational study (COVERALL-2) investigated the immune response after a third dose of SARS-CoV-2 vaccine among patients who were immunocompromised.Patients were enrolled in the following centers: University Hospital Basel (SHCS + STCS), University Hospital Zurich (SHCS + STCS), University Hospital Bern (SHCS), and University Hospital Lausanne (STCS).Patients were eligible to participate in the COVERALL-2 study if they were enrolled in 1 of the 2 cohorts (SHCS or STCS) and received the third SARS-CoV-2 vaccine dose within the frame of their clinical routine (see detailed inclusion and exclusion criteria in Supplementary Material 1 ).

Vaccination and Data Collection
The third vaccine dose-BNT162b2 licensed by Pfizer-BioNTech (Comirnaty; 30 μg of BNT162b2 in 0.3 mL) or mRNA-1273 licensed by Moderna (Spikevax; 50 μg [SHCS] or 100 μg [STCS] of mRNA-1273 in 0.5 mL)-was given to the participants in the frame of their clinical routine, following the vaccine rollout program in Switzerland [13].The study team collected blood samples (EDTA, 2 × 7.5 mL) at baseline (ie, up to 2 weeks before the third vaccination) and at the follow-up visit (ie, 8 weeks after the third vaccination; ±2 weeks).At the time of ethical approval, several patients had already been vaccinated, especially patients with a high risk for severe COVID-19 from the STCS.Therefore, we allowed study participation even if the baseline assessment was missing (ie, no baseline blood sample was available).Baseline variables (ie, before the third vaccination)-such as age, sex, history of cardiovascular or metabolic disease, CD4 T-cell counts, HIV viral load, immunosuppressive therapy, and time from transplant-were routinely collected from the corresponding cohort studies (SHCS and STCS).A test reactive to the nucleocapsid protein (Elecsys Anti-SARS-CoV-2; Roche Diagnostics) was also conducted at the baseline visit, indicating previous contact to SARS-CoV-2.Clinical outcomes and adverse events were assessed during the follow-up visit at 8 weeks (±2 weeks).

Outcomes
The primary outcome was the proportion of patients with a positive antibody (pan-Ig) response to SARS-CoV-2 spike (S1) protein receptor-binding domain (RBD) in human serum or plasma, as assessed by the commercial immunoassay Elecsys Anti-SARS-CoV-2 S (Elecsys S) from Roche Diagnostics [15].We used a cutoff ≥100 U/mL for antibody response, as indicated by Khoury et al [16].Further immunologic endpoints were as follows: • A sensitivity analysis with a threshold ≥0.Data management and collection were done with the REDCap electronic data capture tool [18].

Sample Size
No formal sample size estimation was calculated for the present observational study.We invited the 430 participants of the original COVERALL study (COVERALL-1) to participate [11] and aimed to recruit additional ones from SHCS and STCS to increase our sample size and the precision of our estimates for this study extension (COVERALL-2).

Analysis
Analyses were conducted on 2 data sets.In the first ("strict time window"), we included only those patients from whom we collected results within the prespecified time window (ie, 8 weeks after the third SARS-CoV-2 vaccination, allowing for a time window of ±2 weeks).In the second ("full data set"), we included all patients.We report the frequency, percentage, and Wald 95% confidence intervals (CIs) of serologic immune response to the third vaccine dose.We compared the responses between the vaccine groups using mean difference and 95% CI.No statistical tests were conducted.In addition, all outcomes were stratified by cohort study (SHCS or STCS).Immunologic outcomes were stratified by confirmed SARS-CoV-2 infection or not after the third vaccination.The primary outcome was analyzed by subgroups of interest.These included PLWH with a CD4 T-cell count ≥350 and <350 cells/μL and stratification of individuals by suppressed and unsuppressed HIV viral load (>50 copies/mL).For SOT recipients, we stratified by intense immunosuppressive therapy (triple or quadruple regimen) and less intense (dual regimen).Furthermore, we grouped all study participants according to sex (male or female), age (<60, 60-70, >70 years), and history of cardiovascular diseases or metabolic syndrome (see definition in supplementary material).
Moreover, we assessed the mean immune response separately for PLWH with a CD4 T-cell count <350 cells/μL, PLWH with a CD4 T-cell count ≥350 cells/μL, lung transplant recipients, and kidney transplant recipients.For nonresponders (ie, patients without an antibody response ≥100 U/mL), we exploratorily assessed baseline characteristics, immunosuppression, and vaccine product.We also determined the number of participants who switched the vaccine product (eg, first 2 vaccines Pfizer-BioNTech, third vaccine Moderna).Finally, we compared the antibody response after the third SARS-CoV-2 vaccine with that after basic immunization (after the second vaccine), which was assessed in the previous randomized study (COVERALL-1) in the same patient population (SHCS and STCS) [11,12].Clinical outcomes such as COVID-19 confirmed by PCR or antigen test and patient-reported COVID-19 of household members were reported as frequency with percentage for the different vaccine products.The results solely based on the randomized sample of patients and their antibody responses after the third SARS-CoV-2 vaccine are presented in a separate short report [19].While this report had data on 303 patients (277 SHCS and 26 STCS) who participated in COVERALL-1, the current study was enriched with additional patients from the 2 cohorts.
The order of vaccine products received is shown in Supplementary Table 7.The proportion of patients with an antibody response among participants who switched vaccines was comparable to those who received the same product for all 3 vaccines (Supplementary Table 8).

DISCUSSION
Our results show that a high proportion of patients who were immunocompromised reached an antibody response ≥100 U/mL (Elecsys S test) after the third mRNA SARS-CoV-2 vaccine.Antibody response varied in patients with different levels of immunosuppression.Similar to results after the second SARS-CoV-2 vaccine [11], nearly all PLWH had an antibody response ≥100 U/mL irrespective of CD4 cell counts.Our results are in line with a recently published large systematic review and meta-analysis, concluding that the antibody response in PLWH is comparable to that of the general population [20].For SOT recipients, our results showed that >80% of the included patients had an antibody response ≥100 U/mL after the third SARS-CoV-2 vaccine.This is in sharp contrast to the antibody response of SOT recipients after the second vaccine, where only 23% had an antibody response per the prespecified cutoff (≥100 U/mL) [11].These findings support several other studies assessing the antibody responses in SOT recipients, confirming that these patients particularly    [23][24][25].Yet, the effectiveness of prophylactic monoclonal antibodies is under debate since the appearance of new SARS-CoV-2 omicron variants [26,27].
In terms of safety, the third SARS-CoV-2 vaccine was well tolerated by patients from the SHCS and STCS.Systemic symptoms limiting daily activities were reported by 10% of patients, less than in our previous study assessing the second SARS-CoV-2 vaccine (16% with systemic symptoms [11]).
Our study has the following limitations.First, even though we recruited 601 participants, the sample size for SOT recipient nonresponders is too small to assess the factors associated with insufficient antibody response.As SOT recipients were prioritized when rollout [28] of the third SARS-CoV-2 vaccine began, we were not able to set up the study in time (ie, ensuring funding and ethical approval) and therefore missed a substantial number of eligible patients from the STCS.Adding a study center only partially compensated for this missed opportunity.Furthermore, the treatment of SOT recipients is strongly individualized, and the dosing scheme is not recorded in STCS and could not be included in our analysis.Second, while the majority of patients had a very good antibody response, we observed a considerable number of SARS-CoV-2 infections (42/593, 7.1%).This might raise some concerns about the relevance of our primary endpoint (ie, thresholds for antibody response are under debate [29,30]) and the effectiveness of the vaccines in respect to new variants such as Omicron [31,32].Nevertheless, the vaccines did protect against severe COVID-19 [33][34][35].This is confirmed by our study, where we did not observe any severe COVID-19 cases.Third, a large proportion of baseline blood samples were missing.Therefore, we could not compare the antibody response before and after the third vaccine.We also have limited knowledge about natural infections, which could have caused a rise in antibody response.Last, we did not assess T-cell response, and we were able to include only lung and kidney transplant recipients due to logistical reasons.
In conclusion, a high proportion of patients who were immunocompromised had an antibody response after the third SARS-CoV-2 vaccination, and relatively few vaccine-related adverse events were reported.SOT recipients profited substantially in terms of an increased antibody response between the second and third doses.For patients with low humoral response, alternatives have to be explored.The new bivalent SARS-CoV-2 mRNA vaccines may represent a promising approach.

Figure 1 .
Figure1.Antibody response in patients with immunocompromise after receiving the third SARS-CoV-2 vaccine via the Elecsys S test from Roche.SARS-CoV-2 spike protein receptor-binding domain antibody levels in patients who received the third SARS-CoV-2 vaccine and provided a blood sample at follow-up: people living with HIV with CD4 cell counts <350 or >350 cells/μL and recipients of kidney or lung solid organ transplantation.A value corresponding to half the detection limit (0.2 U/mL) is assigned to measurements below the detection limit (<0.4 U/mL).Horizontal black line, median; box, lower and upper quartiles; whiskers, all samples lying within 1.5 times the IQR.
Any local symptom (redness, swelling, or prolonged pain at the injection site) limiting continuation of normal daily activities during the first 7 days after vaccination • Any systemic symptoms (eg, fever, generalized muscle or joint pain) limiting continuation of normal daily activities during the first 7 days after vaccination • Any vaccine-related symptoms leading to contacting a physician during the first 7 days after vaccination

Table 1 . Baseline Characteristics Before Third Vaccination
Abbreviations: SHCS, Swiss HIV Cohort Study; STCT, Swiss Transplant Cohort Study.a Only patients from the SHCS.b Unsuppressed HIV viral load defined as >50 copies/mL.c Only patients from the STCT.d Intense, triple or quadruple immunosuppressive regimen; less intense, dual immunosuppressive regimen.e Elecsys N test reactive to nucleocapsid protein indicates previous contact to SARS-CoV-2.

Table 2 . Immunologic and Clinical Outcomes
Third SARS-CoV-2 Vaccine in Patients Who Are Immunocompromised • OFID • 5 b Safety outcomes: 12 missing.c Symptoms leading to hospitalization.

Table 3 . Vaccine Responders and Nonresponders in Solid Organ Transplant Recipients After Receiving the Third Dose SARS-CoV-2 Vaccination
Responder according to the full data set (Roche Elecsys Anti SARS-Cov2 S; primary outcome).Abbreviation: IQR: Interquartile range.