In a study, researchers aimed to determine whether the four COVID-19 vaccines licenced for use in Brazil – CoronaVac, Oxford-AstraZeneca (ChAdOx1), Janssen (Ad26.COV2.S) and Pfizer-BioNTech (BNT162b2) – offered additional protection against symptomatic infection, hospitalisation and death, to those reinfected with SARS-CoV-2.

COVID-19 vaccinations are highly effective in preventing symptomatic infection and hospitalisation in individuals who have never been infected, but their efficacy in those infected remains unclear. Knowing how long people are immune after a COVID-19 vaccination is critical as the pandemic continues and additional transmissible variants emerge.

Vaccine efficacy against symptomatic reinfection was 39% for CoronaVac, 56% for Oxford-AstraZeneca, 44% for Janssen, and 66% for Pfizer-BioNTech. It was 90% for Oxford-AstraZeneca, 80% for Janssen, and 80% for Pfizer-BioNTech. In the first 28 days after a positive test, 1,545 individuals were hospitalised, and 290 died.

The extent of protection after COVID-19 infection varies across people. All four of these vaccines have proven to provide extra protection for those with previous COVID-19 infection, reducing hospitalisation and death.