COVID-19 virus rapidly evolves to higher infectivity during in vitro growth, which may be a step toward lower virulence

Attenuated viral vaccines for rubella, measles, yellow fever and other diseases are widely used. Can a similar vaccine be developed for COVID-19? Researchers have now published a foundational study for that possibility. They asked a simple question: Which mutations predominate when the SARS-CoV-2 virus that causes COVID-19 is grown in successive generations — called passages by virologists — in tissue culture?