In the northern hemisphere, the bivalents that are applied here have already stopped being used. The new doses only target Ómicron.
The reason for the swerve is a scientific challenge called immunological imprinting. The world is running behind the capricious changes of the pandemic virus, writes Ruben Navarrette. The circle is vicious: hanging with reinforcements results in more hospitalizations, he says, and the risk of the virus mutating and escaping the immune response.