Single-dose BNT162b2 mRNA COVID-19 vaccine significantly boosts neutralizing antibody response in health care workers recovering from asymptomatic or mild natural SARS-CoV-2 infection

Abstract

Objectives To measure SARS-CoV-2 neutralizing antibody (NtAb) titres in previously infected or uninfected healthcare workers (HCW) who received one or two doses of BNT162b2 mRNA COVID-19 vaccine. Methods NtAbs were titrated as dose inhibiting 50% virus replication (ID 50 ) by live virus microneutralization. Forty-one HCW recovering from mild or asymptomatic infection were evaluated on the day of first-dose vaccination (T1_inf) and 21 days later (T2_inf). Sixteen uninfected HCW were evaluated 20 days after the first dose (T2_uninf) and 20 days after the second dose of vaccine (T3_inf). Results At T2_inf, but not at T1_inf, there was a significant correlation between days from diagnosis (median [IQR] 313 [285-322]) and NtAb levels (p = 0.011). NtAb titres increased at T2_inf with respect to T1_inf (1544 [732-2232] vs. 26 [10-88]; p < 0.001). Likewise, there was a significant increase in NtAb titres at T3_uninf with respect to T2_uninf (183 [111-301] vs. 5 [5-15]; p < 0001). However, NtAb levels at T2_inf were significantly higher than those at T2_uninf and T3_uninf (p < 0.0001 for both analyses). Conclusions A single vaccination in people with mild or asymptomatic previous infection further boosts SARS-CoV-2 humoral immunity to levels higher than those obtained by complete two-vaccination in uninfected subjects.

BNT162b2 mRNA SARS-CoV-2 Vaccine Elicits High Avidity and Neutralizing Antibodies in Healthcare Workers

“…The main limitations of this study are represented by the number of subjects included and the short observation time, which does not permit any inference on vaccine efficacy over time. Antibody persistence will be analyzed in ongoing longitudinal studies, which allows the evaluation of the factors affecting magnitude and persistence of the immune response such as previous exposure to SARS-CoV-2 virus [ 27 , 28 ], age and gender [ 29 , 30 ].…”

The second dose of the BNT162b2 mRNA vaccine does not boost SARS-CoV-2 neutralizing antibody response in previously infected subjects

“…NtAb titers were determined in a live virus assay in VERO E6 cells infected by a lineage B.1 isolate and defined as the reciprocal of the serum dilution decreasing virus replication by 50% (EC 50 ), as measured by the CellTiter-Glo ® Luminescent Cell Viability Assay (Promega) [ 3 ].…”

SARS-CoV-2 mRNA Vaccine Induces Robust Specific and Cross-reactive IgG and Unequal Strain-specific Neutralizing Antibodies in Naïve and Previously Infected Recipients

“…Multiple reports have surfaced recently that previously infected individuals may not need or benefit from a second dose of an mRNA vaccine 24,[44][45][46][47][48] . Our data, by contrast, shows that 1/3 rd of previously infected individuals did not produce detectable levels of neutralizing antibodies after the first dose (Figure 3A, Group 1); after the second dose, however, 40% of these non-responders produced neutralizing antibodies.…”