Contracting COVID-19 may provide some immunity. But still get vaccinated, scientists say

When it comes to acquired immunity against COVID-19, also known as natural immunity, scientists agree that people looking for protection against the coronavirus certainly shouldn't be running out to get intentionally infected.

Yet a number of recent studies — some that suggest prior COVID-19 infection can provide significant immunity and others that suggest vaccination is much more effective — have triggered discussion within the scientific community about the strength of natural immunity.

Many scientists say vaccination is still essential for those who have contracted COVID-19, and that the combination of previous infection and vaccination may actually offer the best level of protection.

Monica Gandhi, a professor of medicine and infectious diseases at the University of California, San Francisco's School of Medicine, is among the experts who believe one dose of vaccine after prior infection offers the best protection. She says the extent of immunity after infection is a very legitimate scientific debate.

"And the problem with this current debate," she said, "is that to ignore natural immunity and say it isn't a thing is leading to a lot of distrust of public health officials."

What goes beyond the bounds of legitimate debate, say many scientists, is the idea being suggested by some other scientists that acquired immunity from infection should be considered as effective or better than vaccination.

"I strongly disagree with that assessment," said Theodora Hatziioannou, a virologist at the Rockerfeller University in New York City.

Acquired immunity is the protection that a person develops to a disease after being infected. In Canada and the U.S., a previous infection is not counted as part of an individual's vaccination status. A person who has had COVID-19 still requires two doses of an approved vaccine to be considered fully vaccinated.

But citizens in many European countries who have had the illness and received a single dose of vaccine are considered fully vaccinated. And in Israel, a person who has recovered from COVID-19 is considered fully vaccinated without having received a shot of vaccine.

From a purely medical perspective, if someone has had a prior infection, they of course should be able to mount an immune response that can protect them for a certain amount of time, said Matthew Miller, an associate professor in the Michael G. DeGroote Institute for Infectious Diseases at McMaster University in Hamilton.

However, most of the studies that have compared the immunity resulting from infection with that of vaccination have found that two doses of vaccine, especially mRNA vaccines, provide higher levels of antibodies than a prior infection, he said.

Dawn Bowdish, Canada Research Chair in Aging and Immunity and a professor at McMaster University, said she's been working with people who were hospitalized with COVID-19 and found they "tend to have pretty robust immune responses because they had quite a bit of time with the virus."

She said immunity from previous infection may be enough for "some of the people, some of the time," but it's "quite proportionate to how sick you got, and there's a lot of variability in people who had low-level infections."

For example, Bowdish recently had someone give blood who had previously been infected with COVID-19 but only with very mild symptoms.