In a new study from the U.K. Health Security Agency, researchers found the highest and most durable protection in people who received one or two doses of COVID-19 vaccine after a primary infection.
They showed that two doses of the BNT162b2 vaccine are associated with high short-term protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which wanes after six months, while immunity remains high for those with infection-acquired immunity boosted with vaccination.
The team examined the duration and effectiveness of immunity in a group of asymptomatic health care workers.
The time to confirmed infection was compared in vaccinated and unvaccinated persons, stratified by previous infection status.
Overall, 27% of the 35,768 participants had a previous SARS-CoV-2 infection.
The researchers found that vaccine coverage was high; 97% had received two doses (78% BNT162b2 with a long interval between doses; 9% BNT162b2 with a short interval; 8% ChAdOx1 nCoV-19 vaccine).
A total of 2,747 primary infections and 210 reinfections were observed between Dec. 7, 2020, and Sept. 21, 2021.
For previously uninfected participants who received BNT162b2 vaccines with a long interval, the adjusted vaccine effectiveness decreased from 85 to 51% at a median of 14 to 73 days and a median of 201 days, respectively, after the second dose; no big difference was seen for those receiving BNT162b2 with a long or short interval.
The vaccine effectiveness at 14 to 73 days after the second dose was 58% among ChAdOx1 nCoV-19 vaccine recipients.
In unvaccinated participants, infection-acquired immunity waned after one year; in those who were subsequently vaccinated, even those infected more than 18 months previously, immunity remained consistently higher than 90%.
The team says the highest and most durable protection was observed in participants who received one or two doses of the COVID-19 vaccine after a primary infection.
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The study is published in the New England Journal of Medicine and was conducted by Victoria Hall et al.
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