Eventually, the virus known as SARS-CoV-2 will become yet “another animal in the zoo,” joining the many other infectious diseases that humanity has learned to live with, predicted Dr. T. Jacob John, who studies viruses and was at the helm of India’s efforts to tackle polio and HIV/AIDS.

But no one knows for sure. The virus is evolving rapidly, and new variants are popping up in different countries. The risk of these new variants was underscored when Novavax Inc. found that the company’s vaccine did not work as well against mutated versions circulating in Britain and South Africa. The more the virus spreads, experts say, the more likely it is that a new variant will become capable of eluding current tests, treatments and vaccines…

While immunity acquired from other coronaviruses — like those that cause the common cold or SARS or MERS — wanes over time, symptoms upon reinfection tend to be milder than the first illness, said Ottar Bjornstad, a co-author of the Science paper who studies viruses at Pennsylvania State University.

“Adults tend not to get very bad symptoms if they’ve already been exposed,” he said.