WASHINGTON — For much of the early phase of the coronavirus pandemic, and after vaccines became widely available, "herd immunity" was considered the goal -- a way out of the pandemic. What about two years in?
“The notion of herd immunity has been largely put aside at the moment,” said Dr. William Schaffner, an infectious diseases expert at Vanderbilt University
Are we still aiming for “herd immunity” against COVID-19?
- Dr. Amesh Adalja, epidemiologist, Johns Hopkins University
- Dr. William Schaffner, infectious diseases expert from Vanderbilt University
While there is "strength in numbers" against the virus, scientists believe COVID-19 is a virus that changes often and will require renewed immunization, like with a vaccine.
WHAT WE FOUND:
Herd immunity, also called “community immunity,” is defined by the CDC as when enough of the population is immune to a disease to make its spread from person to person unlikely.
Diseases like polio and measles aren’t the public health threat they used to be because of community immunity.
“With herd immunity, we have viruses that are usually pretty stable. And once you get infected or get vaccinated, you have long term protection, so that if a substantial proportion of us in the population get protected, we can thereby shelter the people who are immunocompromised,” said Schaffner.
However, this Coronavirus, SARS CoV-2, plays by different rules.
“The virus mutates in a way that gets around our immune system,” said Dr. Amesh Adalja with Johns Hopkins University.
Meaning the virus essentially changes too often for the herd’s immunity to keep up.
“This virus comes from a family of viruses that routinely re-infect us every year and cause 25 to 30% of our common colds,” said Adalja. “We don't have herd immunity to other common cold causing viruses, so it's unlikely to have herd immunity against this type of a coronavirus.”
There is still power in numbers — especially the previously infected and vaccinated ones.
“There's so much more immunity in the environment, that it's harder for this virus to be able to cause severe disease, hospitalization and death at the rate that it once did, because it's increasingly running into people who have immunity against those severe outcomes,” said Adalja.
“This is a protection that we're going to have to renew periodically,” adds Schaffner.
That’s why COVID-19 booster shots have been approved, and scientists are working to learn more about how regular vaccines might become recommended.