By Julie Steenhuysen and Manas Mishra
(Reuters) – People who had previously been infected with COVID-19 were better protected against the Delta variant than those who were vaccinated alone, suggesting that natural immunity was a more potent shield than vaccines against that variant, California and New York health officials reported on Wednesday.
Protection against Delta was highest, however, among people who were both vaccinated and had survived a previous COVID infection, and lowest among those who had never been infected or vaccinated, the study found.
Nevertheless, vaccination remains the safest strategy against COVID-19, according to the report published in U.S. Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report.
The results do not apply to the Omicron variant of the virus, which now accounts for 99.5% of COVID-19 cases in the United States.
“The evidence in this report does not change our vaccination recommendations,” Dr. Ben Silk of the CDC and one of the study’s authors told a media briefing.
“We know that vaccination is still the safest way to protect yourself against COVID-19,” he said.
For the study, health officials in California and New York gathered data from May through November, which included the period when the Delta variant was dominant.
It showed that people who survived a previous infection had lower rates of COVID-19 than people who were vaccinated alone.
But acquiring immunity through natural infection carries significant risks. According to the study, by November 30, 2021, roughly 130,781 residents of California and New York had died from COVID-19.
The analysis did not include information on the severity of initial infection, nor does it account for the full range of illness caused by prior infection.
The CDC said in a statement that prior research had also shown that, over time, vaccination provides greater protection against COVID-19 compared to prior infection alone. One important limitation to the study was that it ended before administration of vaccine booster doses was widespread.
“Viruses are constantly changing, including the virus that causes COVID-19. These changes occur over time and can lead to the emergence of new variants that have new characteristics, including ones that impact the level of immunity vaccination and/or prior infection can provide,” the CDC said in a statement.
Silk said the CDC is studying the impact of vaccination, boosters and prior infection during the Omicron surge and expects to issue further reports when that data becomes available.
“We do know that the safest way to protect yourself from COVID-19 is to be up to date with vaccination,” he said.
(Reporting by Manas Mishra in Bengaluru; Editing by Bill Berkrot)
