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The Centers for Disease Control and Prevention (CDC) released a report of a new study that found that both vaccinations and prior infection help to protect against new COVID-19 infections, though the former has proven far more effective in preventing virus-related hospitalizations.
In the study, researchers evaluated more than a million COVID-19 cases in California and New York to analyze the risk of COVID-19 infection and hospitalizations among four groups: vaccinated with and without prior infection and unvaccinated with and without prior infection.
According to the study, COVID-19 cases and hospitalization rates were highest among unvaccinated subjects who did not have a previous diagnosis.
Researchers said that initially, those with a prior infection had higher case rates than those who were vaccinated with no history of prior infection.
However, once the Delta variant became the dominant strain, people who survived a previous infection had lower case rates than those who were vaccinated alone, according to the study.
During the study, the risk of COVID-19 hospitalizations was “significantly higher” among unvaccinated people with no previous diagnosis than any other group tested.
“Experts first looked at previous infections confirmed with laboratory test by the spring of 2021, when the alpha variant was predominant across the country,” Dr. Benjamin Silk, lead for CDC's surveillance and analytics on the Epi-Task Force said this week. “Before the delta variant, COVID-19 vaccination resulted in better protection against a subsequent infection than surviving a previous infection.
“When looking at the summer and the fall of 2021, when delta became dominant in this country, however, surviving a previous infection now provided greater protection against subsequent infection than vaccination.”
The CDC said in a statement it will publish additional data on COVID-19 vaccines and boosters against the now-dominant Omicron variant later this week.
Researchers said that “Although the epidemiology of COVID-19 might change as new variants emerge, vaccination remains the safest strategy for averting future SARS-CoV-2 infections, hospitalizations, long-term sequelae, and death.”
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