4:13 PM, Feb 27, 2020


Can the US reach COVID-19 herd immunity if not everyone gets vaccinated?

Posted at 9:34 PM, Nov 24, 2020

With news of two highly effective COVID-19 vaccines on the horizon, health officials and scientists are giving us new insight into how we could gain herd immunity.

"If we think of the population as a single group of people with all similar risks and susceptibilities and behaviors, we need 60% of people to be immune, meaning that not only they don’t get sick, but also they don't pass on the virus to other people," says Dr. Stuart Ray, an infectious disease professor and herd immunity expert at Johns Hopkins University.

Dr. Ray says achieving herd immunity with the help of a COVID-19 vaccine would mean enough people would either get the vaccine or already have recovered from the virus and be immune to help stop the spread of the virus.

"It's a little bit like this notion that if you’re going to pass on a message from a lot of people in a group, they have to speak the same language. And the more people don't speak the language, the harder it's going to be to pass that message and there’s a threshold at which the message just gets stopped," says Dr. Ray.

Still, it would take a certain number of people to get the vaccine and have that immunity last in order to reach herd immunity. Stanford University's Dr. Bali Pulendran hopes that we can achieve herd immunity, even though there are a certain number of people who are still hesitant to take the vaccine.

"I think we should remember that a vaccine that is 95% effective is only effective if the majority of people in a population take it. If only half the population or only 60% of the population take it, then we are unlikely to have achieved the level of herd immunity that you need for curbing the disease," says Dr. Pulendran.

And if the new COVID-19 vaccine requires two doses, how crucial will it be to make sure people receive that second round of immunization?

Asked whether follow up will be a concern, Dr. Ray says, "I think it is a possible concern. We’re going to do a lot of learning. So, one of the things we’ve learned is that some vaccines we thought you needed multiple doses, one dose works pretty well."

Doctors say research will be ongoing on the vaccine and the virus itself to ensure people will be protected as much as possible, because so many are hopeful for an end to COVID-19.