Serology study after BTN162b2 vaccination in participants previously infected with SARS-CoV-2 in two different waves versus naïve

Abstract

Background: The antibody response to SARS-CoV-2 mRNA vaccines in individuals with waning immunity generated by a previous SARS-CoV-2 infection, as well as the patterns of IgA and IgM responses in previously infected and in naïve individuals are still poorly understood.

Methods: We performed a serology study in a cohort of BTN162b2 mRNA vaccine recipients who were immunologically naïve (N, n = 50) or had been previously infected with SARS-CoV-2 (P.I., n = 51) during the first (n = 25) or second (n = 26) pandemic waves in Italy, respectively. We measured IgG, IgM and IgA antibodies against the SARS-CoV-2 Spike (S) and IgG against the nucleocapsid (N) proteins, as well as the neutralizing activity of sera collected before vaccination, after the first and second dose of vaccine.

Results: Most P.I. individuals from the first pandemic wave who showed declining antibody titres responded to the first vaccine dose with IgG-S and pseudovirus neutralization titres that were significantly higher than those observed in N individuals after the second vaccine dose. In all recipients, a single dose of vaccine was sufficient to induce a potent IgA response that was not associated with serum neutralization titres. We observed an unconventional pattern of IgM responses that were elicited in only half of immunologically naïve subjects even after the second vaccine dose.

Conclusions: The response to a single dose of vaccine in P.I. individuals is more potent than that observed in N individuals after two doses. Vaccine-induced IgA are not associated with serum neutralization.

Keywords: Medical research; Vaccines; Virology.

Fig. 1. Analysis of the antibody response profile at the time of first vaccination (T0), second vaccination (T1), and 3 weeks after the boost (T2) in naïve and previously infected (P.I.) recipients.

Median values with the interquartile range are displayed. The horizontal dot lines indicate the cutoff value to discriminate positive and negative samples for each assay, according to the manufacturer’s instructions. a IgG for the SARS-CoV-2 nucleocapsid protein N (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I.); b IgM for the spike glycoprotein (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I.); c IgA for the spike glycoprotein (sample sizes: T0 n = 49, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I.); d IgG for the receptor-binding domain (RBD) of the spike (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I); e pseudoviruses neutralization assay, expressed as infectious dose (ID50) (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 50 for P.I.). P values were calculated using the nonparametric two-tailed Wilcoxon matched-pairs signed-rank test for within-group comparisons (bars on top) and the nonparametric Kruskal–Wallis test for between-groups comparisons (bars on bottom). Differences were considered significant if p < 0.05.

Fig. 2. Analysis of the antibody response profile at the time of first vaccination (T0), second vaccination (T1), and 3 weeks after (T2) in subjects infected during the first (orange dots) and the second (red dots) COVID-19 wave.

Median values with the interquartile range are displayed; the horizontal dot lines indicate cutoff value to discriminate positive and negative samples for each assay, according to the manufacturer’s instructions. a IgG for the SARS-CoV-2 nucleocapsid protein N (sample sizes: T0, T1, and T2 n = 25, for P.I. first wave, T0 and T1 n = 26, T2 n = 24 for P.I. second wave); b IgM for the spike glycoprotein (sample sizes: T0, T1, and T2 n = 25, for P.I. first wave, T0 and T1 n = 26, T2 n = 24 for P.I. second wave); c IgA for the spike glycoprotein (sample sizes: T0, T1, and T2 n = 25, for P.I. first wave, T0 and T1 n = 26, T2 n = 24 for P.I. second wave); d IgG for the receptor-binding domain (RBD) of the spike (sample sizes: T0, T1, and T2 n = 25, for P.I. first wave, T0 and T1 n = 26, T2 n = 24 for P.I. second wave); e neutralization assay, expressed as infectious dose (ID50) (sample sizes: T0, T1, and T2 n = 25, for P.I. first wave, T0 and T1 n = 26, T2 n = 25 for P.I. second wave). P values were calculated using the nonparametric two-tailed Wilcoxon matched-pairs signed-rank test for within-group comparisons (bars on top) and the nonparametric Kruskal–Wallis test for between-groups comparisons (bars on bottom). Differences were considered significant if p < 0.05.

Fig. 3. Analysis of the correlation at time of first vaccination (T0), second vaccination (T1), and 3 weeks after (T2) in naïve and previously infected (P.I.) recipients.

a correlation between IgG-S(RBD) and neutralization (ID50) (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I.); b correlation between IgG-S(RBD) and IgA (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I.); c correlation between neutralization (ID50) and IgA-S (sample sizes: T0 n = 48, T1 n = 50, T2 n = 49 for naïve, T0 and T1 n = 51, T2 n = 49 for P.I.). The correlation was calculated using the two-sided Spearmen rank-correlation test.

Fig. 4. Antibody response in naïve and previously infected (P.I.) male (blue dots) and female (red dots) subjects following vaccination.

a IgG-S(RBD) titers at the time of first vaccination (T0, n. males/females 12/36 for naïve, 19/32 for P.I.), second vaccination (T1, n. males/females 13/37 for naïve, 19/32 for P.I.), and 3 weeks after the boost (T2, n. males/females 13/36 for naïve, 19/30 for P.I.); b neutralization activity expressed as ID50 (n. males/females: T0 12/36, T1 13/37, T2 13/36 for naïve, T0 19/32, T1 19/32, T2 19/31 for P.I.); c IgA-S antibody titers (n. males/females: T0 12/37, T1 13/37, T2 13/36 for naïve, T0 19/32, T1 19/32, T2 18/31 for P.I.). P values were calculated using the Wilcoxon matched-pairs signed ranked test and considered significant if p < 0.05.