COVID Vaccines Offer Lasting Protection against Reinfection: Studies
The authors said that the study, which spanned the Delta variant surge in Israel, “supports a public health policy of vaccinating patients who have recovered from Covid-19, particularly in places where the delta variant is still of concern.”
Sustained 90% Protection When Vaccine Follows Infection
A prospective study led by UK Health Security Agency researchers evaluated the effectiveness and duration of COVID-19 vaccination in a group of asymptomatic UK healthcare workers who underwent testing for infection every 2 weeks, as well as monthly antibody testing.
The team compared the time to SARS-CoV-2 infection among unvaccinated participants and those who received the Pfizer or AstraZeneca/Oxford COVID-19 vaccine up to 10 months before, stratified by whether they had been previously infected. Median age was 46 years, and 84% were women.
Among 35,768 participants, 27% had recovered from COVID-19, as evidenced by the presence of SARS-CoV-2 antibodies. Nearly all participants (97%) had received two vaccine doses; 78% of them had received the Pfizer vaccine with a long interval (6 weeks or more) between doses, while 9% received the same vaccine with a short interval (less than 6 weeks) between doses, and 8% had received the AstraZeneca vaccine.
From Dec 7, 2020, to Sep 21, 2021, there were 2,747 primary SARS-CoV-2 infections and 210 reinfections. Among COVID-19–naïve participants in the long-interval Pfizer group, adjusted vaccine effectiveness fell from 85% 14 to 73 days after the second dose to 51% at a median of 201 days. Effectiveness was not significantly different between the long- and short-interval groups.
Among AstraZeneca vaccine recipients, adjusted vaccine effectiveness was 58% after the second dose, much lower than among Pfizer vaccinees.
Unvaccinated participants saw waning of infection-acquired immunity after 1 year, although efficacy stayed higher than 90% in those who were vaccinated after infection, even in those infected more than 18 months before.
Overall, 357 participants (13%) with primary infection reported a hospital visit for COVID-19, compared with 18 (9%) of those with reinfection.
“Two doses of BNT162b2 vaccine were associated with high short-term protection against SARS-CoV-2 infection; this protection waned considerably after 6 months,” amid the UK Delta surge, the authors said. “Infection-acquired immunity boosted with vaccination remained high more than 1 year after infection.”
They conclude, “Strategic use of booster doses of vaccine to avert waning of protection (particularly in double-vaccinated, previously uninfected persons) may reduce infection and transmission in the ongoing response to Covid-19.”
Sequence of Infection, Vaccination May Matter
In an audio interview in the same issue on both studies, as well as another on the antiviral combination nirmatrelvir-ritonavir in COVID-19 patients, Eric Rubin, MD, PhD, NEJM editor-in-chief, and Deputy Editor Lindsey Baden, MD, said that immune response can vary depending on which SARS-CoV-2 strain caused natural infection and whether natural infection or vaccination occurred first.
“The sequence of these events—vaccination followed by natural infection or natural infection followed by vaccination—may have very different consequences and implications for the immune increasing and then the subsequent immune boosting,” Rubin said.
He said that COVID-19 survivors can still benefit from subsequent vaccination, although the ideal time to vaccinate is yet unknown: “There is an advantage, and although the absolute risk difference may be small, it’s real. Also, there doesn’t appear to be a safety issue with getting boosted.”
Mary Van Beusekom is editorial consultant and content manager at CIDRAP. This article is published courtesy of the University of Minnesota’s Center for Infectious Diseases Research and Policy (CIDRAP).
