By Ethan Covey

Results from a small case series found that reinfection with COVID-19 can happen quickly, even within a couple of weeks of previous infection.

While the findings specifically highlight infections caused by the particularly contagious delta and omicron variants, they provide important context for the study of future variants and reinforce the importance of vaccination (MMWR Morb Mortal Wkly Rep 2022;71:524-526).

“This series confirms what many people have suspected based on observations or personal experiences, that COVID-19 reinfections are possible within a very short window of time—at least in the period of transition between delta variant predominance and omicron variant predominance,” said Brian F. Borah, MD, an epidemiologist with the CDC Epidemic Intelligence Service and Vermont Department of Health.

The report focuses on 10 cases from four states—Rhode Island, Vermont, Washington and Wisconsin. In each case, whole-genome sequencing confirmed omicron variant infections in patients who had been infected with the delta variant within the previous 90 days.

Of the 10 patients, one had completed a two-dose messenger RNA COVID-19 primary vaccination series six to 10 weeks before the first infection. Two other patients had received a single COVID-19 vaccination dose in the time between infections. The other seven patients were unvaccinated.

The length of time from initial infection to reinfection ranged from 23 to 87 days, with a median of 54.5 days.

“I think there is a misperception that if you have had COVID-19, then you are completely protected from another infection for at least 90 days,” Dr. Borah told Infectious Disease Special Edition. “While many people do likely have some degree of protection following an infection, this case series demonstrates that COVID-19 reinfections are possible, even just 23 days after a previous infection.”

Dr. Borah noted that the findings are specific to the period between delta and omicron variant predominance, but they underscore what he called the “immune-evasive nature” of the omicron variant.

Yet, the findings also highlight the general limits of infection-induced immunity against novel variants, he added.

“Omicron is unlikely to be the last variant that we will see, and new variants might also have immune-evasive features that cause early reinfections,” Dr. Borah said. “There might also be more than one variant in circulation at the same time. All these things should add to our understanding that COVID-19 reinfection is more than just a theoretical risk.”

Consequently, mitigation strategies remain important, as do continued efforts to promote COVID-19 vaccination and the receipt of booster doses.

Dr. Borah hopes future research will be able to identify a few areas that could benefit from additional study.

“We could learn more about how common reinfections are, and how common‘“early reinfections’ are specifically,” he said. “Most evidence suggests that reinfections overall are rare, but data are still limited. Second, we don’t know much about the severity of reinfections compared to first infections. We think that reinfection cases are generally milder, but further studies would be useful. Third, it will be important to learn more about whether having multiple COVID-19 infections is associated with any increased risk of ‘“long COVID’ or other post-acute sequelae.”

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