For months, we’ve waited for a vaccine that would put an end to the coronavirus pandemic and help us return to normalcy. Now that the vaccines are finally here, the big question on everyone's minds is – What do we do next?

Newly released guidance from the Centers for Disease Control (CDC) says it’s safe for vaccinated people to gather indoors in small groups without masks, including with unvaccinated people who are at low risk of experiencing a severe COVID-19 illness. But experts warn it’s not time to start planning your big post-pandemic shindig just yet. 

In order to stop the virus from circulating, we need to achieve something called herd immunity. That happens when so many people have either had the virus or been vaccinated against it that there are no longer enough hosts left to transmit it from person to person. 

The threshold for herd immunity varies from virus to virus depending on how easily the contagion spreads. For example, the measles virus has a very high herd immunity threshold of around 95%, according to the World Health Organization (WHO), but for polio, the herd immunity threshold is about 80%. 

For COVID-19, scientists believe that number is at least 70%, and until we reach that point, the virus continues to be a threat. As new, more contagious variants are identified, it reveals the risk that more deadly surges are still possible.

Both the Pfizer and Moderna vaccines, which require two doses given about three weeks apart, are about 95% effective against the predominant strain of the virus currently circulating in the U.S. The one-dose Johnson & Johnson vaccine is around 72% effective in the United States. 

But the vaccines may be less effective against new variants, like the one first discovered in South Africa. Yale Medicine immunologist Akiko Iwasaki told Spectrum News that the decreased efficacy can be attributed to the way the virus has mutated in some variants. 

"The antibody and the spike protein is like lock and key," explains Iwasaki. "So it has to fit perfectly for the antibody to block that virus replication. So imagine the key changing its shape so that the lock doesn't fit anymore. And that's kind of the situation that we might be facing with the [variant detected in South Africa].”

A less effective vaccine also means there is a higher chance a person could spread the virus even after being vaccinated. It also raises the threshold for reaching herd immunity, meaning even more people will need to be vaccinated in order to stop the spread of the virus. 

Jeffrey Shaman, who directs the climate and health program at Columbia Mailman School of Public Health, says we should all be cautious: "The real key thing is that we have to not get too celebratory early on."

For those still waiting for their shots, experts say to continue to wear masks and avoid gathering indoors with other unvaccinated people, especially those who are at high risk of experiencing severe COVID illnesses.