California and New York health officials say people who had previously been infected with COVID-19 were better protected against the Delta variant than those who were vaccinated alone, as reported in Fidelity.

However, the study found that protection against Delta was highest 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 results do not apply to the Omicron variant of the virus, which now accounts for 99.5% of COVID-19 cases in the US.

"The evidence in this report does not change our vaccination recommendations," said Ben Silk of the CDC and one of the study's authors, adding "we know that vaccination is still the safest way to protect yourself against COVID-19."