In an explosive Senate hearing on March 18, Dr. Anthony Fauci clashed with Kentucky Sen. Rand Paul over a subject that has characterized much of the White House health adviser’s recent commentary on Covid-19: the specter of reinfection, caused by one of the emerging variants of the virus.Several recent studies suggest that both natural and vaccine-induced immunity to Covid-19 is robust at least for the medium term, and even those hinting at possible reinfections suggest it is a rare phenomenon mainly afflicting people with severely weakened immune systems.Fauci nonetheless maintains that reinfections, particularly from the South African variant of the...