Infectious Disease

Previous infection protects against COVID-19 for several months

January 29, 2022

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The authors report no relevant financial information.

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People previously infected with SARS-CoV-2 are essentially protected against COVID-19 for several months, even without vaccination, according to a study.

Additionally, however, their natural immunity is declining but can be boosted with vaccination, researchers reported in results of a study conducted between December 16, 2020 and December 27, 2021 among staff at the Cleveland Clinic.

COVID-19_Variant_409578937

Individuals previously infected with SARS-CoV-2 remain protected from COVID-19 for several months, although this protection wanes and patients become vulnerable to symptomatic COVID-19. Source: Adobe Stock.

The investigation period included the emergence of the delta and omicron variants of SARS-CoV-2. The researchers found that natural immunity several months old does not protect against the Omicron variant.

“The arrival of the Omicron variant has greatly altered the risk of COVID-19 for all individuals, whether or not they were previously infected and whether or not they were previously vaccinated.” Nabin K Shrestha, MD, MPH, a medical officer in the Cleveland Clinic’s infectious diseases unit, Healio said. “Protection against COVID-19 from previous infection or vaccination may be of shorter duration than before the arrival of the omicron variant.”

Shrestha and colleagues included staff from the Cleveland Clinic working on December 16, 2020, the day vaccinations began. According to the study, anyone who had previously tested positive for COVID-19 at least once was considered to be pre-infected. Researchers examined the cumulative incidence of COVID-19, symptomatic COVID-19, and hospitalizations for COVID-19 over the next year.

“It’s important to note that the study was conducted on an active population of healthcare workers,” Shrestha said. “There were no children, very few elderly people and probably only a few immunocompromised people.”

Of the 52,238 employees enrolled, 9% were previously infected and 71% were vaccinated at the end of the study. The cumulative incidence of COVID-19 throughout the study was “substantially higher” among previously unvaccinated subjects who were unvaccinated than any other group, although it was lower among the vaccinated than among the unvaccinated and lower among those who were unvaccinated those previously infected than those not, the researchers said.

The study data also showed that the incidence of COVID-19 increased “dramatically” in all groups after the emergence of omicron, although vaccination was associated with a significantly lower risk of symptomatic COVID-19 in both the pre-omicron (HR = 0.6 ; 95% CI, 0.4-0.9) and omicron (HR = 0.36; 95% CI, 0.23-0.57) phases.

“The Omicron variant differs significantly from previous variants in the speed at which it spreads and its ability to infect previously infected or vaccinated individuals, which was unusual in previous variants,” Shrestha said. “What was true of previous variants in terms of immunity and vaccine efficacy should not be true of the Omicron variant without proper investigation.”

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