More than 20 coronavirus vaccines are in human testing, according to the World Health Organization. So far, small, early studies of most advanced vaccines found they were generally safe and triggered immune responses but weren’t designed to prove whether they actually protected people.
A series of large, final-stage trials are getting under way that, for the first time, will decisively test whether coronavirus vaccines prevent or reduce risk of Covid-19, including 30,000-person studies for vaccines from Moderna Inc. and from Pfizer Inc. and its partner, BioNTech SE, slated to start by the end of July.
The new studies will be “event-driven,” which means researchers expect to learn whether the vaccines are working once a certain number of study subjects come down with Covid-19, the disease caused by the new coronavirus.
Initially researchers thought it could take many months to accrue enough Covid-19 cases among study subjects to yield answers because lockdown measures slowed the spread of the virus and the hot summer weather threatened to slow it further.
But Covid-19 counts are rising in countries such as Brazil, Peru and South Africa. Cases have also flared in parts of the U.S. since mid-June, particularly in states such as California, Texas and Florida.
“Because of the bad situation in the U.S., we might actually get a very quick readout for vaccines,” possibly in October, [said Moderna’s Stephane Bancel.]