Antibody-mediated Immunogenicity against SARS-CoV-2 following priming, boosting and hybrid immunity: insights from 11 months of follow-up of a healthcare worker cohort in Israel, December 2020-October 2021

BackgroundWe determined circulating anti-S SARS-CoV-2 IgG antibody titres in a vaccinated healthcare workers (HCWs) cohort from Northern Israel in the 11 months following primary vaccination according to age, ethnicity, boosting timing and previous infection status. MethodsAll consenting HCWs were invited to have their circulating IgG levels measured before vaccination and at 6 subsequent timepoints. All HCWs with suspected COVID-19 were PCR tested. We described trends in circulating IgG geometric mean concentration by age, ethnicity, timing of boosting and previous infection status and compared strata using Kruskall-Wallis tests. ResultsAmong 985 vaccinated HCWs. IgG titres gradually decreased in all groups over the study duration. Younger or previously infected individuals had higher initial IgG levels (p<0.001 in both cases); differences substantially decreased or disappeared at 7-9 months, before boosting. Pre-infection IgG levels in infected participants were similar to levels measured at the same timepoint in HCWs who remained uninfected (p>0.3). IgG GMC in those boosted 6-7 months after dose 2 was lower compared with those boosted 8-9 months after (1999-vs 2736, p=0.02). ConclusionsImmunity waned 6 months post-priming in all age groups and in previously infected individuals, reversed by boosting. IgG titres decrease among previously infected individuals and the proportion of reinfected individuals in this group, comparable to the proportion of breakthrough infection in previously uninfected individuals suggests individuals with hybrid immunity (infection+vaccination) may also require further doses. Our study also highlights the difficulty in determining protective IgG levels and the need to clarify the optimal timing in 3 dose regimens

SARS-CoV-2 Immunogenicity in individuals infected before and after COVID-19 vaccination: Israel, January-March 2021: Implications for vaccination policy

Between December 2020-March 2021 we measured anti-SARS-CoV-2 IgG titers post-vaccination with the BNT162b2 vaccine among 725 Israeli hospital workers. Previously infected individuals who received one dose had higher IgG titres than fully vaccinated, never-infected workers. Post-vaccination infection did not increase IgG titres. Individuals infected post-dose one should receive the second.

Impact of age, gender, ethnicity and prior disease status on immunogenicity following administration of a single dose of the BNT162b2 mRNA Covid-19 Vaccine: real-world evidence from Israeli healthcare workers, December-January 2020

The Pfizer Covid-19 vaccine showed high efficacy in clinical trials but observational data from populations not included in trials are needed. We described immunogenicity 21 days post-dose 1 among 514 Israeli healthcare workers by age, gender, ethnicity and prior COVID19 infection. Immunogenicity was similar by gender and ethnicity but decreased with age. Those with prior infection had antibody titres one magnitude order higher than naive individuals regardless of the presence of detectable IgG antibodies pre-vaccination.