Journal Watch
February 25, 2022
How Useful Is Vaccination After COVID-19 Infection?
Abigail Zuger, MD, reviewing Hall V et al. N Engl J Med 2022 Feb 16 Hammerman A et al. N Engl J Med 2022 Feb 16
Two studies document
significant reductions in reinfection rates when natural immunity is bolstered by vaccine.
Although natural infection with COVID-19 offers some protection against reinfection, researchers are still probing just how natural immunity compares with vaccine-induced immunity and how vaccines can best be deployed to enhance natural immunity.
In a prospective U.K. study, investigators followed >35,000 asymptomatic healthcare workers (84% female; median age, 46) from December 2020 to September 2021 with biweekly SARS-CoV-2 PCR tests. About 9000 had a history of COVID-19 prior to enrollment; in this group, risk for reinfection was initially about 86% lower than among the other participants. By 1 year after infection, this reduction in risk had fallen to about 70%. With one or two subsequent immunizations (almost all with the Pfizer-BioNTech BNT162b2 vaccine), reduction in risk for reinfection climbed to ≥90%, with no signs of waning protection over the study's duration. By contrast, among the approximately 26,000 participants with no history of COVID-19, two doses of BNT162b2 initially reduced risk for infection by about 85%, but this protection declined to about 50% by 6–7 months after the second dose of vaccine. Extending the time between vaccine doses to >6 weeks did not affect these results substantially.
In a retrospective study from Israel, researchers reviewed charts of almost 150,000 patients who had recovered from COVID-19 between August 2020 and May 2021. Among about 66,000 who remained unvaccinated, 2168 were reinfected by the end of November 2021 (10.2 cases per 100,000 per day), while among about 83,000 who received one or two subsequent doses of BNT162b2, only 354 were reinfected (2.5 cases per 100,000 per day), for an estimated vaccine effectiveness of 82%. Receipt of two postinfection vaccine doses did not appear to confer more protection than did a single dose.
COMMENT
These studies did not track the clinical severity of the COVID-19 reinfections they document, nor do the authors speculate on how the appearance of new viral variants during the study might have affected the results. Neither study details whether vaccine side effects were more pronounced in previously infected recipients. Still, with the understanding that the exact clinical toll from any COVID-19 reinfection is not entirely clear for either vaccinated or unvaccinated patients, incidence of reinfection can clearly be markedly reduced with a single vaccination after natural infection.
CITATION(S):
Hall V et al. Protection against SARS-CoV-2 after Covid-19 vaccination and previous infection. N Engl J Med 2022 Feb 16; [e-pub]. (Δεν είναι ορατοί οι σύνδεσμοι (links).
Εγγραφή ή
Είσοδος)
Hammerman A et al. Effectiveness of the BNT162b2 vaccine after recovery from Covid-19. N Engl J Med 2022 Feb 16; [e-pub]. (Δεν είναι ορατοί οι σύνδεσμοι (links).
Εγγραφή ή
Είσοδος)
Θέμα: Κορονοϊός ( COVID-19 ) (Αναγνώστηκε 261957 φορές)
24 Απριλίου 2020, 01:44:56