Natural immunity from COVID-19 may be weaker in people who've had severe disease
Some survivors of severe COVID-19 have hoped their grueling battle might give them some natural protection against getting severe COVID a second time. However, research out of UT Health San Antonio has found that these people may be at higher risk than others of getting sick with COVID again.
Evelien Bunnik, Ph.D., is an assistant professor of microbiology, immunology and molecular genetics at UT Health San Antonio Graduate School of Biomedical Sciences. She also runs the Bunnik Lab, where she and her team are studying COVID immunity.
When a person is infected with COVID, Bunnik said, the immune system has a couple of important jobs. The first and most important job is to isolate and eliminate the viral invader, and the second is to learn from that fight.
“The immune system remembers all the viruses and all the bacteria, all the pathogens that we've encountered in our lives, so that the next time you see the same virus, you develop a better and faster immune response,” Bunnik explained.
However, in some people, the COVID virus confuses their immune system.
"The immune system goes haywire and becomes over activated," Bunnik said, "And we were wondering what the effect of that was on the formation of immunological memory."
Bunnick’s lab decided to look specifically at B cells, which make antibodies to fight a given pathogen the next time it comes around. They have published a paper on what they found.
"There are certain markers that we look at to see which are the cells that really give you the best type of memory response," she said, "And so we saw more of those good memory B cells in people who had mild disease, and not so much in people had severe disease."
All of the people Bunnik studied had been hospitalized, but some only needed supportive care. Those are the ones she categorized as having mild disease. Others were quite ill, and needed help breathing with mechanical ventilators. That was the severe disease group.
The B cells in people in the severe disease group just didn’t seem to learn as well.
"What we think this means is that people who have mild disease, their immune system, in general, probably works better, which may in part be the reason they have milder disease in the first place." Bunnik concluded. "As a result of that, they also produce a better memory response. We predict that means these people are better protected against the next infection than people who had more severe disease."
So, according to Bunnik’s research, it doesn’t look like severe COVID survivors should rely on natural immunity to protect them from a second bout with COVID.
"No, absolutely not," she said. "I think it is really important, especially for these people to get vaccinated."
Bunnik stressed, however, that all of the patients in her lab's study were infected with earlier variants of the COVID virus and before vaccines were available. Because the virus has evolved, it is essential, she said, for everyone to get vaccinated, not just those are at high risk for or who have had severe COVID-19.