In a cohort of BNT162b2 (Pfizer–BioNTech) mRNA vaccine recipients (n = 1,090), we observed that spike-specific IgG antibody levels and ACE2 antibody binding inhibition responses elicited by a single vaccine dose in individuals with prior SARS-CoV-2 infection (n = 35) were similar to those seen after two doses of vaccine in individuals without prior infection (n = 228). Post-vaccine symptoms were more prominent for those with prior infection after the first dose, but symptomology was similar between groups after the second dose.

Importance Certain individuals, when infected by SARS-CoV-2, tend to develop the more severe forms of Covid-19 illness for reasons that remain unclear. Objective To determine the demographic and clinical characteristics associated with increased severity of Covid-19 infection. Design Retrospective observational study. We curated data from the electronic health record, and used multivariable logistic regression to examine the association of pre-existing traits with a Covid-19 illness severity defined by level of required care: need for hospital admission, need for intensive care, and need for intubation. Setting A large, multihospital healthcare system in Southern California.

Background. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused over one million deaths worldwide, thus there is an urgent need to develop preventive and therapeutic strategies. The anti-tuberculosis vaccine Bacillus Calmette-Guérin (BCG) demonstrates nonspecific protective innate immune-boosting effects. Here, we determined if history of BCG vaccination was associated with decreased SARS-CoV-2 infection and seroconversion in a longitudinal, retrospective observational study of a diverse cohort of healthcare workers (HCWs). Methods. We assessed SARS-CoV-2 seroprevalence and collected medical questionnaires, including BCG vaccination status and pre-existing demographic and clinical characteristics, from an observational cohort of HCWs in a multi-site Los Angeles healthcare organization. We used multivariate analysis to estimate if history of BCG vaccination was associated with decreased rates of SARS-CoV-2 infection and seroconversion. Results. Of the 6,201 HCWs, 29.6% reported a history of BCG vaccination whereas 68.9% did not receive BCG vaccination. Seroprevalence of anti-SARS-CoV-2 IgG as well as incidence of self-reported clinical symptoms associated with COVID-19 were significantly decreased among HCWs with a history of BCG vaccination compared to those without BCG vaccination. After adjusting for age and sex, we found that history of BCG vaccination, but not meningococcal, pneumococcal or influenza vaccination, was associated with decreased SARS-CoV-2 IgG seroconversion. Conclusions. History of BCG vaccination was associated with decreased seroprevalence of anti-SARS-CoV-2 IgG and reduced reported COVID-19-related clinical symptoms in this cohort of HCWs. Therefore, large randomized prospective clinical trials of BCG vaccination are urgently needed to confirm if BCG vaccination can induced a protective effect against SARS-CoV2 infection.