Some scientists have argued that it would be better to use the scarce vaccines to give first doses to as many people as possible, so the maximum number of people have at least partial immunity. That could help slow the spread of the virus.
[Investigator Paul] Bieniasz worries that would also hasten the evolution of new strains of virus.
Scientists simply don’t know how this will play out. For one thing, it’s unclear whether the first shot of a vaccine is strong enough to prevent the virus from multiplying inside someone and being abundant enough to spread to somebody else. If the virus can’t spread, how it has evolved in an individual becomes irrelevant.
Extending the time between the first and second dose of a vaccine “does run the risk of promoting evolution,” says Andrew Read, an evolutionary microbiologist at Penn State University. But he adds, “I must say, at the moment, that seems like a second-order issue compared to just reducing the transmission through the population as a whole.”