Editor’s note: This article was updated in August 2021 to reflect the latest information.

We know that natural infection with SARS-CoV-2, the virus that caused COVID-19, generates some immunity. Should you rely on this for protection and skip the vaccine if you were previously infected? The answer is a clear ‘no’.

Natural infection is clearly effective for preventing reinfection with the virus for several months. A large study in England reported an 84% reduction in the risk of infection in people previously infected, and the protective effect lasted at least 7 months. Other studies have reported a similar low risk of reinfection. However, these studies were mostly done before the delta variant emerged, and it’s not clear if prior infection will protect against the delta variant.

So why should people get vaccinated if they were previously infected?

Vaccination has two important benefits for people previously infected: a single dose of vaccine will strongly boost neutralizing antibody levels—these are antibodies that inactivate the virus, and higher levels are associated with greater protection. The second benefit comes from a different part of the immune system. Vaccination activates immune T-cells that increase protection against severe illness and against variant strains.

A recent CDC study confirms the benefit of vaccination in people with prior natural infection. The study compared people in Kentucky who did and did not get vaccinated after natural infection with SARS-CoV-2. Those who remained unvaccinated had a 2-fold increased risk of reinfection compared to those who were vaccinated after the first infection.

“The delta variant is a game-changer—it spreads far more easily and may cause more severe illness compared to earlier strains,” said Dr. Edward Belongia, an epidemiologist with Marshfield Clinic Research Institute who conducts research on COVID-19. “COVID-19 hospitalizations are increasing rapidly among people who are unvaccinated. Even if you have some natural immunity from infection, it makes sense to get vaccinated for the greatest protection against delta.”

For more information about the COVID-19 vaccine, talk to your provider.