Having two vaccines is good. But three is better — and it could make a major difference in getting the pandemic under control.

"It could be a total game changer," said Dr. Muriel Jean-Jacques, an assistant professor of medicine at Northwestern University.

Millions of doses of the Covid-19 vaccine developed by Johnson & Johnson will soon be available in the U.S., a much-anticipated development that could help turn the tide of the pandemic by vastly speeding the rate at which people are vaccinated.

Experts say the newly authorized vaccine could play a key role in staving off another surge of infections, particularly as the recent sharp declines in reported cases of Covid-19 appear to be leveling off and rising once again.

"We've never had to vaccinate our whole population at the same time before — not to mention the rest of the world — so having more vaccines will make that easier," Jean-Jacques said.