In-Depth: Why people who recovered from COVID still need to get vaccinated

Variants a threat, but 'hybrid immunity' powerful
Pfizer COVID-19 vaccine
Posted at 5:15 PM, Jun 25, 2021
and last updated 2021-06-25 21:33:00-04

SAN DIEGO (KGTV) -- Two studies published Friday underscore why people with a previous COVID infection should get vaccinated.

The research, published in Science, shows hybrid immunity is far more powerful than protection from infection or vaccination alone.

“Those people make superhuman immune responses,” said Dr. Shane Crotty, a professor at the La Jolla Institute for Immunology who wrote an analysis of the papers for Science.

Studies show people with natural immunity from an infection can be more susceptible to certain variants than people who are vaccinated, particularly to variants of concern like Gamma from Brazil or Beta from South Africa.

In Brazil, one study found the effectiveness of natural immunity against the Gamma variant dropped from about 90 percent to about 60 percent. Early research on the Delta variant discovered in India shows it is similarly elusive to natural immunity, although mRNA vaccines remain highly effective against it.

However, once someone with natural immunity gets vaccinated, the research in Science found they generate about 100 times more antibodies to the Beta variant than people with natural immunity alone, and about 25 times more antibodies than vaccination alone.

The findings reinforce what the Centers for Disease Control and Prevention has been saying all along. “People that have already had COVID-19 should still get vaccinated,” Crotty said. “We know natural immunity is not as protective as vaccine immunity for at least some of these variants.”

In general, natural immunity to a pathogen tends to be stronger than vaccination, but a study published in June helps explain why it’s the other way around with COVID.

A team in Seattle found the COVID vaccines produce a lot more protective antibodies to the stretch of the virus that grabs on to cells, an area called the Receptor-Binding Domain.

That means, if a vaccinated person encounters a mutated virus, they’ll have a broader selection of backup antibodies for that region than people with natural immunity.

Scientists aren’t sure why the COVID vaccines offer this kind of superior response since both are based on the virus’ spike protein. One theory is that the vaccines present a training protein to the immune system in a slightly different way.

Another theory has to do with the method of delivery to the immune system: in a mild natural infection, most of the immune response is confined to the respiratory tract. Vaccines generate an immune response in the muscle, “where the immune system may have an even better chance of seeing it and responding vigorously,” wrote National Institutes of Health Director Dr. Francis Collins in a blog this week.