Alliance for Pandemic Preparedness

April 9, 2021

Single-Dose BNT162b2 Vaccine Protects against Asymptomatic SARS-CoV-2 Infection

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  • A study of health care workers (N=~9,000) employed at Cambridge University Hospitals in Great Britain found that 1 dose of the Pfizer-BioNTech COVID-19 vaccine was associated with a 4-fold reduction in asymptomatic SARS-CoV-2 infection ≥12 days post-vaccination, from 0.8% to 0.2% [EDITORIAL NOTE: This is equivalent to a 75% vaccine efficacy].  Additionally, the median cycle threshold value of positive tests among those who became infected showed a non-significant increasing trend of higher viral loads among unvaccinated HCWs compared to HCWs ≥12 days post- vaccination, potentially indicating that vaccinated individuals who subsequently become infected may have lower viral loads. The authors suggest that mass first-dose vaccination may reduce SARS-CoV-2 transmission. 

Jones et al. (Apr 8, 2021). Single-Dose BNT162b2 Vaccine Protects against Asymptomatic SARS-CoV-2 Infection. ELife. https://doi.org/10.7554/eLife.68808