As some people have now been vaccinated for more than half a year, evidence is pouring in about Covid vaccine efficacy. When evaluating vaccine efficacy, it is important to distinguish between efficacy against infection, symptomatic disease, and transmission versus efficacy against hospitalization and death. For infection and symptomatic disease, the COVID-19 vaccines are not as efficacious as hoped, with immunity gradually waning after a few months. For hospitalization and death, immunity is stronger, lasting for at least six months. The gestalt of the findings implies that the infection explosion globally that we have been experiencing– post double vaccination in e.g. Israel, UK, US etc. –may be due to the vaccinated spreading Covid as much or more than the unvaccinated. A natural question to ask is whether vaccines with limited capacity to prevent symptomatic disease may drive the evolution of more virulent strains? In a PLoS Biology article from 2015, Read et al. …