Neutralization of SARS-CoV-2 Omicron and other variants in serum from children with vaccination-induced myocarditis

Abstract Our study demonstrates that children who developed SARS-CoV-2 vaccination-induced myocarditis and may not receive another vaccination, could be susceptible to infection with Omicron and emerging variants. We observed higher neutralizing antibody titers in myocarditis patients vs. healthy vaccinated children, but significantly lower neutralization titers against Omicron in both groups.

The emergence of Omicron variant of SARS-CoV-2 resulted in rapid spread 2 across the globe. As of February 2022, the World Health Organization had defined five 3 SARS-CoV-2 variants of concern (VOCs); Alpha, Beta, Gamma, Delta, Omicron) as well 4 as two variants of interest (VOIs); Lambda, and Mu [1]. Viral spike protein of Omicron 5 contains over 30 mutations, raising concerns that Omicron could be resistant to 6 neutralizing antibodies generated following SARS-CoV-2 vaccination [2], and a third 7 vaccine dose may be required to boost immunity [3]. Even though SARS-CoV-2 mRNA 8 vaccines have been safe and effective in providing protection against COVID-19, under 9 rare circumstances SARS-CoV-2 mRNA vaccination may result in temporary, self-10 resolving vaccine-induced myocarditis in some younger individuals [4,5]. 11 Booster vaccine doses are approved in United States for individuals >12 years of 12 age. Children who developed rare SARS-CoV-2 vaccination-induced myocarditis are 13 potentially at risk of another reactive cardiac episode following vaccination, and 14 therefore, may not receive a third vaccine dose. However, there is no information on 15 neutralization response to Omicron variant in children with vaccine-induced myocarditis. 16 Moreover, the capacity of children with vaccine-induced myocarditis during the acute-17 phase myocarditis and post-acute recovery stage to elicit neutralizing antibodies against 18 the prototype vaccine strain and variants of concern (VOCs), especially against the fast-19 spreading Omicron variant, is unknown. In absence of a vaccine booster dose, these 20 children could be at risk for breakthrough infection, especially from the Omicron variant.

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Hence, it is important to determine the capacity of vaccine-induced antibodies to 22 neutralize SARS-CoV-2 VOCs/VOIs in these children.  Table S1). All children prior to 10 vaccination were SARS-CoV-2 naïve by SARS-CoV-2 PCR and antibody-negative  with authentic SARS-CoV-2 virus) in previous studies [6]. 3 Pseudovirions were produced as previously described [6]. The neutralization 4 assays were performed as previously described [7] [8,9]. Briefly, 50 µL of SARS-CoV-2 5 S pseudovirions (~200,000 relative light units) were pre-incubated with 3-fold serial 6 dilutions (20-fold starting dilution) of heat-inactivated serum for 1h. Then virus-antibody 7 mixtures were added to 293T-ACE2-TMPRSS2 cells (10 4 cells/50 μL) [6] [5]. Cells were 8 lysed 24 h later, and luciferase activity was measured using One-Glo luciferase assay 9 system (Promega, Cat# E6130). The assay of each serum was performed in duplicate, 10 and the 50% neutralization titer was calculated using Prism 9 (GraphPad Software). The 11 limit of detection for the neutralization assay is 1:20. Two independent biological 12 replicate experiments were performed for each sample and variation in PsVNA50 titers 13 was <9% between replicates.  End-point titer was determined as 2-fold above the average absorbance values of 20 serum binding to blank control wells. The end-point titer is reported as the last serum 21 dilution that was above this cutoff.

Seroreactivity of pediatric samples to SARS-CoV-2 RBD by ELISA
Descriptive statistics were performed to determine the geometric mean titer 2 (GMT) neutralizing values or mean end-point titers and were calculated using 3 GraphPad. All experimental data to compare differences among groups were analyzed 4 using lme4 and emmeans packages in R (RStudio version 1.1.463). Since age and sex 5 can be biologically plausible confounders, data were analyzed for statistical significance 6 between groups to control for age and sex as covariates (predictor variables) using a 7 multivariate linear regression model, and the sample size was small. To ensure 8 robustness of the results, absolute measurements were log2-transformed before 9 performing the analysis. For comparisons between the vaccine groups (factor variable), 10 pairwise comparisons were extracted using 'emmeans' and Tukey-adjusted p values 11 were used for denoting significance to reduce Type 1 error due to multiple testing. The 12 tests were two-sided tests. The differences were considered statistically significant with 13 a 95% confidence interval when the p value was less than 0.05.  Table S3).

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Our data demonstrate that neutralizing antibodies elicited by two doses of 20 vaccine could provide protection against the highly mutated Omicron variant in some 21 children but suggests the need for vaccine boosters in children for maximum protection.

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Children with vaccination-induced myocarditis made a robust antibody response that