Covid-19 cases are falling in the U.S. It could be a calm before a variant-driven storm

STAT News writes about the recent drop in new cases in the United States and the changes in the virus that could cause rapid growth again.

What could also be happening, said infectious disease expert Kristian Andersen of Scripps Research Institute, is that the variants, which share some mutations, are just better at reinfecting people who already had a case of Covid-19.

Brazil and South Africa both had major outbreaks earlier in the pandemic, so there should be some decently high level of population immunity in those countries. Lab experiments have shown the variants can partially evade the immune response generated after an infection, so it’s possible the two strains are able to circulate to an extent among people who have already been infected. Other types of the virus might not be able to do that — they’re blocked by the existing immunity — and the result is that P.1 and B.1.351 grow in prevalence while other variants are curtailed.