More worrisome are two new strains: one in South Africa and one in Brazil. Lab studies indicate that the antibodies generated by the Moderna and Pfizer vaccines are less effective against the South African strain than against the previously dominant strain. It remains unclear how much difference this will make in people because the studies indicate that antibodies still work well enough to provide significant protection, and also because antibodies comprise only one part of the immune response; the variant might still be just as vulnerable to T-cells, memory B cells and the rest of our bodies’ immune response.

But it’s still troubling, and scientists are now preparing a booster shot designed specifically for the mutated spike protein of this strain.

More troubling may be the strain which has surfaced in Manaus, a Brazilian city of 2.2 million where an estimated 76 percent of the population has been infected and therefore should have enough naturally acquired immunity to constrain, if not suffocate, the spread of covid-19. That was the case for a while. But a new strain similar to the one in South Africa emerged, and infections caused by it are surging again in Manaus. This strongly suggests the virus has acquired the ability to evade naturally acquired immunity.