Vaccination and Blood Specimen Collection

Participants received either BNT162b2 or mRNA-1273 through their respective employers based on vaccine availability. Employees of UCLA Health primarily received BNT162b2, while those of LACoFD primarily received mRNA-1273.

We classified participants as either not previously infected (NPI) or previously infected (PI) with SARS-CoV-2 prior to receipt of the first vaccine dose. Participants were categorized as previously infected if they had a positive SARS-CoV-2 RT-PCR from a mid-turbinate or nasopharyngeal swab or had detectable IgG antibody to either the RBD portion of the S protein (anti-Spike) [15] or to the N protein (anti-Nucleocapsid) [16] prior to immunization. Participants were categorized as NPI if they had negative nasal swabs, negative serology and no symptomatic history suggestive of infection prior to their first dose of vaccine. Participants with a history of anosmia and/or ageusia without a positive PCR or antibody test were not classified and therefore not included in any comparisons that required classification.

Participants had blood drawn between 7 days after the first vaccine dose and just prior to the second dose (up to 20 days after the first dose of BNT162b2 and up to 27 days after the first dose of mRNA-1273). Blood was also collected 7–30 days, 31–60 days and 61–90 days after completion of the two-dose series. Not all participants provided blood samples at every time point due to missed appointments or blood draw refusal.