Study shows strong natural immunity to Covid-19 after 10 months

A new study, published in The Lancet, has found that individuals who have been infected with Covid-19 possess strong immunity to the virus for at least 10 months after their initial infection. The research shows that this immunity provides good protection against symptomatic illness and reduces the risk of severe illness.

Largest review yet of available data

Conducted by the Institute for Health Metrics and Evaluation Covid-19 Forecasting Team, the study is the largest review of available data on the subject, comprising a meta-analysis of 65 studies from 19 countries. The findings suggest that natural immunity to the virus is strong against all variants of the coronavirus, including Omicron.

Long-term protection and vaccination

Dr. Chris Murray, the director of the Institute for Health Metrics and Evaluation at the University of Washington, expressed surprise at the study's results: “There’s quite a long sustained protection against severe disease and death, almost 90% at 10 months. It is much better than I had expected, and that’s a good thing for the world, right? Given that most of the world has had Omicron, it means there’s an awful lot of immunity out there.”

However, the study's authors caution that unlike with other viral infections such as measles or chickenpox, protection from Covid-19 does not last forever. Even people who have natural immunity will probably still require an annual Covid-19 booster. With natural immunity lasting as long as it does, people do not need to receive a shot more than once a year.

Reduced protection against Omicron BA.1 subvariant

The research also found that individuals who got sick with any pre-Omicron version of the coronavirus had substantially reduced protection against infection from the BA.1 subvariant of Omicron: only 36% at 10 months after infection. Nevertheless, protection from infection appears to be at least equivalent to two doses of mRNA vaccine, at least for the variants through BA.1.

Importance of vaccination

While natural immunity is protective, the study's authors emphasize that vaccination remains the safest way to acquire immunity. As of February 8, only about 69% of the total US population has received their primary vaccine series, and only about 16% have received a dose of the updated booster, according to the US Centers for Disease Control and Prevention.

Monitoring for future variants

Dr. Claudia Hoyen, an infectious disease specialist and director of pediatric infection control at UH Rainbow Babies and Children’s Hospital in Cleveland, who was not involved in the new study, notes that Covid-19 is here to stay, and the new study makes a good argument for continuing to monitor for future variants. The higher the level of overall immunity in a population, the less likely it is that an even more dangerous variant could develop.

Limitations of the study

The study had some limitations, including a lack of research on natural immunity in Africa and incomplete information about infection status and hospital admissions. There were also only a small number of studies that looked at BA.1 and its sublineages, making it necessary to continue monitoring and analyzing variants.

“What we all worry about is a new variant that has immune escape like Omicron had on the prior variants,” Murray said. “People like to hope the evolution of the virus will lead to less severe forms, but that’s not a guarantee. So we just need to stay vigilant for the possibility of a different variant.”