Antibody Response to 1 Dose SARS-CoV-2 mRNA Vaccine in Previously Infected HCWs

Antibody titer responses to a single dose of mRNA vaccine were higher in health care workers (HCWs) with previous SARS-CoV-2 infections than those without, according to a research letter published in JAMA Network. In the face of global vaccine shortages, investigators believe this finding could inform single-dose vaccine strategies for previously infected individuals or support lowering their place on the priority list.

A total of 3816 HCWs were enrolled in a sero-survey study conducted in August 2020. Of those, 151 HCWs were randomly contacted, and 59 volunteers enrolled. In the volunteer group, 17 were previously identified as SARS-CoV-2 IgG antibody negative (Ab-negative), 16 IgG-positive with asymptomatic COVID-19 (asymptomatic), and 26 IgG-positive with symptomatic COVID-19 (symptomatic). Participants were vaccinated with either the Pfizer-BioNTech or Moderna vaccine and had their blood drawn at 0, 7, and 14 days.

At each sampling day, the median reciprocal half-maximal binding titers were higher in the asymptomatic (208, 29,364, and 34,033) and symptomatic (302, 32,301, and 35,460) groups vs the Ab-negative group (<50, <50, and 924) (P < .001 for each). Median reciprocal ID₉₉ virus neutralization titers at day 0 and 14 were 80 and 40,960 for the asymptomatic group and 320 and 40,960 for the symptomatic group, both of which again were higher than the Ab-negative group (<20 and 80) (P < .001 for each).

The study was limited by a small sample size and potential bias because the sample may not be representative of the original population. Furthermore, vaccine efficacy data was insufficient.

Investigators did conclude that HCWs with previous COVID-19 (as diagnosed via laboratory-confirmed serology testing) had higher antibody titer responses, which could inform prioritizations of vaccines and potential single-dose vaccination strategy.