Second-generation Covid-19 vaccines are built for impact over speed

Some of the world's most prolific and experienced vaccine developers -- Sanofi, GlaxoSmithKline and Merck & Co - are among at least 100 challengers trailing the leaders

Speed isn’t the only thing that matters in the quest for a vaccine to end the Covid-19 pandemic. They may not cross the finish line first, but dozens of companies and universities still see an opening for inoculations that prevent more infections, provide lasting immunity, protect older and more vulnerable people, yield massive quantities or ship easily throughout the world. Those are benefits the front-runners may not be able to deliver.

“Is it the tortoise or the hare?” said Seth Berkley, chief executive officer of Gavi, the Vaccine Alliance, a global non-profit focused on access to immunizations. “There may be