The coronavirus has been shrouded in unknowns and uncertainties since it emerged a little more than a year ago, and one of the biggest questions has been whether people can get reinfected, and if so, how quickly. There have been isolated reports of people having a second case of covid-19, the disease caused by the virus, but that appears to be rare, and the new study bolsters the case that immunity usually persists.
The review of blood samples from nearly 200 patients also saw that multiple elements of the immune system — not just antibodies — continued to be effective at recognizing and responding to the virus. The human body appears to retain a memory of the invader and is poised to generate a coordinated counterattack of antibodies and killer T cells quickly if exposed again.
This comes amid concerns about mutant variants of the coronavirus, including one originally identified in the United Kingdom and spreading rapidly there. As of Thursday afternoon it had been seen in seven states in the United States, including two new additions, Texas and Pennsylvania.
Scientists have been generally optimistic that these variants will be unable to escape the onslaught of the human immune system. But no one is taking any chances. Officials at the Centers for Disease Control and Prevention are ramping up a strain surveillance program to improve the genomic sequencing that allows scientists to study mutations.
The authors of the new study said they believe their findings would apply to the United Kingdom variant as well as the more common coronavirus. The reason: The immune responses target hundreds of different pieces of the virus, few of which are affected by the mutations seen so far. The consensus is that the coronavirus would need a tremendous number of transmission-enhancing mutations in concert to evade natural or vaccine-induced immunity.
“There’s a lot of different arms of the immune system recognizing the virus. So if you have a mutation, it wouldn’t evade all these different arms,” said Daniela Weiskopf, a co-author of the study and a researcher at the La Jolla Institute for Immunology.
The immune response to a virus builds gradually, peaks, then begins to contract — but can reach a plateau, and stay there for a long period. After eight months, Weiskopf said, most people who have been infected by the coronavirus and recovered appear to have relatively stable immunity.
“It’s not decaying any further. Based on that, it might be good for many more months, or years,” Weiskopf said.
The full duration of immunity has to remain speculative for now, because the novel coronavirus has been circulating in human beings for barely a year and there isn’t long-term data. The oldest specimens studied by the La Jolla team were obtained about nine months ago, Weiskopf said.
Stanley Perlman, a University of Iowa virologist who was not part of the research team, said the study is welcome news given that some early reports last spring suggested that immunity to the coronavirus might wane quickly.
“This is more believable, and this is done well. This supports the notion that there’s going to be immunity for some period of time,” Perlman said.
It is still possible for someone with immunity to get infected by the coronavirus without becoming sick, Perlman noted. The immune response is unlikely to be sterilizing. “People get infected, but they don’t get affected,” he said.
There is one obvious cautionary note in the new research: About 10 percent of people infected with the coronavirus see their immune response degrade. There is no clear explanation for why this happens in some people. The human immune system is enormously complex, and the immune response varies greatly from person to person.
“The kind of immunity you get from natural infection is very variable. And it’s kind of reminiscent of the fact that we can have a tremendous variability in clinical outcomes” from coronavirus infections, said study co-author Alessandro Sette, also with the La Jolla Institute.
What that means in practical terms is that people who have gotten sick with the virus, or have had a positive test result, cannot know with certainty that they’re in the 90 percent who have lingering immunity, Sette said.
“If I had covid, I would still not throw away my masks, I would not go to rave parties. People still need to be responsible,” Sette said. “It’s like driving a car where you know you have 90 percent probability that the brakes work.”
Still, this encouraging scientific result suggests that the human immune system is up to the job of dealing with this novel coronavirus.
“I cannot tell you what it’s going to be looking like two years from now, because the virus hasn’t been around two years,” Sette said. “But from the looks of it, I wouldn’t be surprised if the immunity would last for years.”