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People who don't get vaccinated against COVID-19 should expect to be reinfected with the coronavirus every 16 to 17 months on average, according to a recent study published in The Lancet Microbe.
Since COVID-19 hasn't existed for long enough to perform a long-term study, researchers at Yale University and the University of North Carolina at Charlotte looked at reinfection data for six other human-infecting coronaviruses, including SARS and MERS.
"Reinfection can reasonably happen in three months or less," Jeffrey Townsend, lead study author and a biostatistics professor at the Yale School of Public Health, said in a statement.
"Therefore, those who have been naturally infected should get vaccinated," he said. "Previous infection alone can offer very little long-term protection against subsequent infections."
The research team looked at post-infection data for six coronaviruses between 1984-2020 and found reinfection ranged from 128 days to 28 years. They calculated that reinfection with COVID-19 would likely occur between 3 months to 5 years after peak antibody response, with an average of 16 months. This is less than half the duration seen for other coronaviruses that circulate among humans.
The risk of COVID-19 reinfection is about 5% at three months, which jumps to 50% after 17 months, the research team found. Reinfection could become increasingly common as immunity wanes and new variants develop, they said.
"We tend to think about immunity as being immune or not immune. Our study cautions that we instead should be more focused on the risk of reinfection through time," Alex Dornburg, senior study author and assistant professor of bioinformatics and genomics at UNC, said in the statement.
"As new variants arise, previous immune responses become less effective at combating the virus," he said. "Those who were naturally infected early in the pandemic are increasingly likely to become reinfected in the near future."
Study estimates are based on average times of declining immunity across different coronaviruses, the researchers told the Yale Daily News. At the individual level, people have different levels of immunity, which can provide shorter or longer duration of protection based on immune status, immunity within a community, age, underlying health conditions, environmental exposure, and other factors.
The research team said that preventive health measures and global distribution of vaccines will be "critical" in minimizing reinfection and COVID-19 deaths. In areas with low vaccination rates, for instance, unvaccinated people should continue safety practices such as social distancing, wearing masks, and proper indoor ventilation to avoid reinfection.
"We need to be very aware of the fact that this disease is likely to be circulating over the long term and that we don't have this long-term immunity that many people seem to be hoping to rely on in order to protect them from disease," Townsend told the newspaper.
The Lancet Microbe: "The durability of immunity against reinfection by SARS-CoV-2: a comparative evolutionary study."
Inside UNC Charlotte: "For unvaccinated, reinfection by SARS-CoV-2 is likely."
Yale Daily News: "COVID-19 reinfection is likely among unvaccinated individuals, Yale study finds."
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Cite this: Unvaccinated People Likely to Catch COVID Repeatedly - Medscape - Oct 25, 2021.