People who had previously been infected with COVID-19 were better protected against the Delta variant than those who were vaccinated only, suggesting that natural immunity was a more potent shield than vaccines against that variant, California and New York health officials reported on Wednesday (Jan 19).
Protection against Delta was highest, however, among people who were both vaccinated and had survived a previous COVID-19 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 the US 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 per cent 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 last year, 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 only.
That represented a change from the period when the Alpha variant was dominant, Silk told the briefing.
“Before the Delta variant, COVID-19 vaccination resulted in better protection against a subsequent infection than surviving a previous infection,” he said.
In the summer and fall of 2021, however, when Delta became the predominant circulating iteration of the virus in the United States, “surviving a previous infection now provided greater protection against the subsequent infection than vaccination”, he said.