Scientists See Signs of Lasting Immunity to Covid-19, Even After Mild Infections

 ... Scientists who have been monitoring immune responses to the virus are now starting to see encouraging signs of strong, lasting immunity, even in people who developed only mild symptoms of Covid-19, a flurry of new studies suggests. Disease-fighting antibodies, as well as immune cells called B cells and T cells that are capable of recognizing the virus, appear to persist months after infections have resolved — an encouraging echo of the body’s enduring response to other viruses.

“Things are really working as they’re supposed to,” said Deepta Bhattacharya, an immunologist at the University of Arizona and an author on one of the new studies, which has not yet been peer-reviewed.

Although researchers cannot forecast how long these immune responses will last, many experts consider the data a welcome indication that the body’s most studious cells are doing their job — and will have a good chance of fending off the coronavirus, faster and more fervently than before, if exposed to it again.

“This is exactly what you would hope for,” said Marion Pepper, an immunologist at the University of Washington and an author on another of the new studies, which is currently under review at the journal Nature. “All the pieces are there to have a totally protective immune response.”

Protection against reinfection cannot be fully confirmed until there is proof that most people who encounter the virus a second time are actually able to keep it at bay, Dr. Pepper said. But the findings could help quell recent concerns over the virus’s ability to dupe the immune system into amnesia, leaving people vulnerable to repeat bouts of disease.

Researchers have yet to find unambiguous evidence that coronavirus reinfections are occurring, especially within the few months that the virus has been rippling through the human population. The prospect of immune memory “helps to explain that,” Dr. Pepper said....