Unvaccinated people can expect COVID-19 infections every 16 months, study suggests

Number of Americans unvaccinated against COVID-19 still 'unacceptably high,' Biden says

President Joe Biden gave an update on America’s COVID-19 vaccination progress as the rate of administering the shots picked up in recent days.

NEW HAVEN, Conn. - Scholars at the Yale School of Public Health say we still don’t have enough empirical data to know how long natural immunity lasts after COVID-19 infections, but the results of their recent study appear to indicate it doesn’t last very long.

The study, published on Oct. 1 in The Lancet Microbe, suggests unvaccinated people are at risk of reinfection 16 months after recovering from COVID-19.

The study showed an unvaccinated person runs a 5% risk of reinfection roughly three months after recovery. But once they reached the 16-month mark, that risk increased to 50% — essentially reducing their odds to a coin toss.

"As the COVID-19 pandemic continues, reinfection is likely to become increasingly common," the study said. "Maintaining public health measures that curb transmission — including among individuals who were previously infected with SARS-CoV-2 — coupled with persistent efforts to accelerate vaccination worldwide is critical to the prevention of COVID-19 morbidity and mortality."

Jeffrey Townsend, the study’s lead author and Yale professor of biostatistics, told the Yale Daily News it can take several years to determine the rate of reinfection for infectious diseases. Having emerged in late 2019, the novel coronavirus hasn’t circulated enough for scientists to have the data necessary to answer such a question.

To compensate for the lack of COVI-19 data, researchers looked into data on other coronaviruses — like the Middle Eastern Respiratory Syndrome (MERS).

Using what is already known about those viruses, how they evolve and how they’re related to each other, researchers constructed the model for COVID-19 reinfections.

Nurse Heather Esmer draws a syringe before administering a Covid-19 vaccine booster at Birkenhead Medical Building in Birkenhead, Merseyside. Picture date: Saturday October 23, 2021. (Photo by Martin Rickett/PA Images via Getty Images)

"This is an instance where we have no idea about the answer to something and the only way that we can obtain that answer is through evolutionary biology," Townsend said. "And we managed to obtain it, and I’m very confident in the result."

Given the frequency in which mankind battles coronaviruses like the common cold, Townsend said he was not surprised by the results of the study. But he acknowledges COVID-19 infections carry more dangerous outcomes than common illnesses.

He also said news reports comparing natural immunity through COVID-19 infections with the immunity achieved through flu or measles infections are misleading. Townsend emphasized these viruses are not closely related and it’s a misconception to think COVID-19 infections provide lifelong immunity.

This story was reported from Atlanta.