(HealthDay News) — Two doses of 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, according to a study published online Feb. 16 in the New England Journal of Medicine.
Victoria Hall, from the U.K. Health Security Agency in London, and colleagues examined the duration and effectiveness of immunity in a prospective cohort of asymptomatic health care workers. The time to confirmed infection was compared in vaccinated and unvaccinated persons, stratified by previous infection status.
Overall, 27 percent of the 35,768 participants had a previous SARS-CoV-2 infection. The researchers found that vaccine coverage was high; 97 percent had received two doses (78 percent BNT162b2 with a long interval between doses; 9 percent BNT162b2 with a short interval; 8 percent 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 percent at a median of 14 to 73 days and a median of 201 days, respectively, after the second dose; no significant difference was seen for those receiving BNT162b2 with a long or short interval. The adjusted vaccine effectiveness at 14 to 73 days after the second dose was 58 percent 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 percent.
“The highest and most durable protection was observed in participants who received one or two doses of vaccine after a primary infection,” the authors write.
One author disclosed financial ties to the pharmaceutical industry.