“Does immunity protect an individual from disease on reinfection?” writes Yale immunobiology researcher Akiko Iwasaki in an accompanying editorial in The Lancet Infectious Diseases. “The answer is not necessarily.”
Previous research has shown that neutralizing antibodies — immune system proteins that latch onto pathogens and prevent them from infecting cells — can wane in the months after a Covid-19 infection, particularly when the initial infection was mild. Some wondered if that meant the end of herd immunity hopes.
In the Nevada case, we know that “the patient had positive antibodies after the reinfection, but whether he had pre-existing antibody after the first infection is unknown,” writes Iwasaki.
Immunity could mean a strong antibody response, which prevents the virus from establishing itself in cells. But it could also mean a good killer T-cell response, which could potentially stop an infection very quickly: before you feel sick and before you start spreading the virus to others.
“In many infections, the virus does reproduce a little bit, but then the immune response stops this infection in its tracks,” [immunologist Alessandro] Sette explains. Also possible: “You do get infected, you do get sick, but your immune system does enough of a job curbing the infection, so you don’t get as sick.”