Health experts worry COVID-19 vaccine skepticism could put herd immunity at risk

Every week, millions of Americans are getting vaccinated against COVID-19, but health officials and medical experts worry that a growing number of vaccine skeptics who refuse to get a shot will put the possibility of herd immunity at risk. 

So far, more than 66 million Americans have been fully vaccinated against the novel coronavirus, according to the latest data from the U.S. Centers for Disease Control and Prevention. 

But a significant number of Americans have expressed reluctance to get the shot, even in places where they are plentiful. Twenty-five percent said they probably or definitely will not get vaccinated, according to a poll from The Associated Press-NORC Center for Public Affairs Research that was released on April 2. 

They are leery about possible side effects. They tend to be Republican, and they are usually younger and less susceptible to becoming critically ill or dying if they catch COVID-19.

There’s been a slight shift, though, since the first weeks of the nation’s largest-ever vaccination campaign, which began in mid-December. An AP-NORC poll conducted in late January showed that 67% of adult Americans were willing to get vaccinated or had already received at least one shot. Now that figure has climbed to 75%.

Epidemiologists define the herd immunity threshold for a given virus as the percentage of the population that must be immune to ensure that its introduction will not cause an outbreak. If enough people are immune, an infected person will likely come into contact only with people who are already immune rather than spreading the virus to someone who is susceptible. 

RELATED: Sunlight, humidity ‘unlikely’ impacts on how COVID-19 spreads, Homeland Security study finds

Dr. Anthony Fauci, the nation’s foremost expert on infectious diseases, estimated that somewhere between 70% and 85% of the U.S. population needs to get inoculated to stop the scourge that has killed more than 560,000 Americans. Recently, he said the spread of more contagious variants of the virus increases the need for more people to get their shots — and quickly.

Still, any sustained level of reluctance to get vaccinated makes health experts concerned that the threshold for herd immunity might not be reached. 

Deborah Fuller, a professor with the University of Washington School of Medicine, said if the herd immunity level cannot be reached soon, a more realistic target could be vaccinating at least 50% of the population by this summer, with a higher vaccination rate among the most vulnerable to reduce severe disease, hospitalizations and deaths.

"In this scenario, the virus would persist in the population but cease being a major health threat that overburdens our health care systems," Fuller said.

Fauci said it’s entirely possible the U.S. — and the rest of the world — won’t ever meet the threshold for herd immunity, but said it’s not an "all or none phenomenon." 

"You don’t want to make herd immunity an all or none phenomenon here because it’s somewhat of an elusive number and elusive concept, because it’s not only who gets vaccinated, but it’s also who was infected and is now protected against reinfection," he explained. "So, you could wind up getting to where you want to get because the unfortunate people who don’t want to get vaccinated could get infected and might be protected because of their infection."

Highly transmissible COVID-19 mutations like the B.1.1.7 variant that originated in the U.K., are a major concern to health experts like Fauci, but he expressed confidence in the vaccines’ effectiveness against that specific strain.

RELATED: Fauci says variants are ‘wild card’ in COVID-19 booster vaccine equation

But the effectiveness of existing vaccines against emerging variants is not guaranteed.

"You know, variants are a risk to anyone who is not fully protected against it," Fauci said. "So, for example, there are some variants – like B.1.1.7 – that vaccines cover them very well. There are other variants, like B.1.351 from South Africa, where protection against any symptomatic disease diminishes by a fair amount, but protection against severe disease, hospitalization and deaths is very good."

Many who are skeptical of getting a shot have expressed doubts about the vaccine’s safety and effectiveness, despite a U.S. vaccination drive that has encountered few serious side effects. 

In the latest AP-NORC poll, Republicans remained more likely than Democrats to say they will probably or definitely not get vaccinated, 36% compared with 12%. But somewhat fewer Republicans today are reluctant. Back in January, 44% said they would shy away from a vaccine.

The hesitance can be seen in Alabama’s rural Winston County, which is 96% White and where more than 90% of voters backed then-President Donald Trump last year. Only 6.9% of the county’s roughly 24,000 residents are fully vaccinated, the lowest level in Alabama.

But across the country, health care workers and public health departments are doing what they can to get the message out there: Get vaccinated. 

Elsewhere in Alabama, health officials tried to counter problems that include reluctance in heavily Black areas where distrust of government medical initiatives runs deep. They targeted a few counties with a pro-vaccine message, especially in the old plantation region where a large percentage of the population is Black and many are poor.

The campaign enlisted doctors and pastors and used virtual meetings and the radio to spread the word.

Dr. Karen Landers, assistant state health officer, said the effort had positive results. For example, in Perry County, where 68% of the population of about 9,300 is Black, more than 16% of the population is fully vaccinated, among the highest levels. Officials likely will make similar efforts for other parts of the state, she said.

On March 31, Gov. Roy Cooper, a Democrat, tweeted a video of him getting a free doughnut from the Krispy Kreme chain. Customers who show their vaccine card can get a free doughnut every day for the rest of the year.

"Do it today, guys!" Cooper encouraged viewers. Nearly 36% of North Carolina adults have been at least partially vaccinated, state data show.

This story was reported from Los Angeles. The Associated Press contributed.