Protection file

Previous infection, vaccines offer the best protection against COVID


NEW YORK (AP) — A new two-state study that compares coronavirus protection from prior infection and vaccination finds that getting vaccinated is still the safest way to prevent COVID-19.

The study looked at infections in New York and California last summer and fall and found that people who were both vaccinated and had survived a previous episode of COVID-19 were the most protected.

But unvaccinated people with past infection came second. In the fall, when the more contagious delta variant had taken over but boosters were not yet widespread, this group had a lower case rate than vaccinated people who had no previous infection.

The Centers for Disease Control and Prevention, which released the study on Wednesday, noted several caveats about the research. And some outside experts were wary of the results and wary of how they might be interpreted.

“The key message is that from a symptomatic COVID infection, you generate some immunity,” said immunologist E. John Wherry of the University of Pennsylvania. “But it’s still much safer to get your immunity through vaccination than through infection.”

Vaccination has long been encouraged even after a previous case of COVID-19 because both types of protection eventually wane – and there are too many unknowns to rely solely on past infection, especially an old one, added immunologist Ali Ellebedy at the University of Washington. in Saint Louis.

“There are so many variables that you can’t control that you just can’t use it to say, ‘Oh, I’m infected, so I’m protected,'” Ellebedy said.

The research corresponds to a small group of studies that found that unvaccinated people who had previous infection had lower risks of being diagnosed with or ill with COVID-19 than vaccinated people who had never been infected before.

The results of the new study make sense, said Christine Petersen, an epidemiologist at the University of Iowa. She said a vaccine developed against an earlier form of the coronavirus would likely become less and less effective against new mutated versions.

However, experts say there are a number of other possible factors at play, including whether the effectiveness of the vaccine has simply waned over time in many people and to what extent mask-wearing and other behaviors played a role in what happened.

Another thing to consider: The “definitely unvaccinated” aren’t likely to be tested, and the study included only lab-confirmed cases, Wherry said.

“We may not be picking up as many reinfections in the unvaccinated group,” he said.

CDC officials noted other limitations. The study was done before the omicron variant took over and before many Americans received booster doses, which have been shown to dramatically amplify protection by increasing levels of anti-virus antibodies. . The analysis also did not include information about the severity of past infections, or the risk of serious illness or death from COVID-19.

The study authors concluded that vaccination “remains the safest strategy” to prevent infections and “all eligible persons should be up to date with vaccination against COVID-19”.

The researchers looked at infections in California and New York, which together make up about 18% of the US population. They also looked at COVID-19-related hospitalizations in California.

Overall, about 70% of adults in each state have been vaccinated; another 5% have been vaccinated and have had a previous infection. Just under 20% were unvaccinated; and about 5% were unvaccinated but had previously had an infection.

The researchers looked at COVID-19 cases from late last May to mid-November and calculated how often new infections occurred in each group. Over time, protection by vaccine alone seemed less and less impressive.

In early October, compared to unvaccinated people who had no previous infection, the case rates were:

– 6 times lower in California and 4.5 times lower in New York in those who have been vaccinated but not infected before.

– 29 times less in California and 15 times less in New York among those who had been infected but never vaccinated.

— 32.5 times less in California and 20 times less in New York among those who had been infected and vaccinated.

But the difference in rates between the latter two groups was not statistically significant, the researchers found.

Hospitalization data, only in California, followed a similar trend.


AP Medical Writer Lauran Neergaard contributed.


The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute Department of Science Education. The AP is solely responsible for all content.