High Vaccination Rates Are Helping These Countries Reach Herd Immunity

While vaccine effort across the United States continues to face resistance, other countries may be close to achieving herd immunity, thanks to their vaccine programs. 

Spain, a country once hard-hit by COVID-19, now has more than 80% of its population fully vaccinated and is seeing a decline in new cases. The United Arab Emirates has nearly 90% of its citizens inoculated and life has largely returned to normal.

Closer to home, at least 74% of the entire population of Puerto Rico are fully vaccinated, compared to 59% in the U.S. as a whole.

Jesús Rodríguez Baño, the head of infectious diseases at the Virgen de la Macarena Hospital in Seville, Spain, told The Lancet that while it’s still unclear how much of the population needs to be immune to reach herd immunity, the "very high" vaccination rate in Spain is "the only plausible explanation" for the decline in COVID-19 cases and hospitalizations.

What Does Herd Immunity Look Like Now? 

Herd immunity refers to when a large percentage of a population is immune to a disease either through natural immunity or vaccination. Earlier in the pandemic, some experts suspected herd immunity to require at least 60-70% of a population to have protection against COVID-19.

In reality, that number is now in the high 80s range, said Jennifer Lighter, MD, an infectious disease specialist and hospital epidemiologist with NYU Langone Health.

She told Verywell that the idea of herd immunity is nuanced—it’s not as simple as reaching a certain threshold of vaccination or natural infection in a community and then forgetting about COVID-19—especially as variants continue to circulate.

She said that combating COVID-19 requires different tactics for different populations. For older populations and those at risk for severe illness, booster helps ensure the best protection long-term. On the other hand, children may have a strong enough immune response to the first doses of the vaccine that they may not need a booster anytime soon.

“It's really about immune protection,” she said. “It's not just everyone gets their primary series [of vaccines] and boom we're done. We need to show that a large population is really protected.” 

Countries with smaller populations may be more successful in rolling out mass vaccination campaigns.

Michael Oglesbee, PhD, director of the Infectious Disease Institute at Ohio State University, said that the U.S. has varying levels of COVID-19 precautions in different states, such as mask mandates. The inconsistent measures make it challenging to achieve a level of mass protection across the country.

"If you're a vaccinated individual from Maine coming to Ohio, your chance of coming into contact with an unvaccinated, infected individual increases dramatically, which means you could be infected," he told Verywell.

“It's that heterogeneity in the landscape that’s a huge challenge," he added.

How Will Waning Vaccine Efficacies Affect Herd Immunity?

Since vaccine efficacies can wane over time, booster doses are necessary to keep high-risk groups immune. In Spain, booster shots are being administered to people aged 70 and above.

“We also have this issue of breakthrough infections, where somebody who has previously been infected or previously has been vaccinated, can be susceptible to infection again,” Oglesbee said. “That probably reflects waning immunity, which is why we're putting so much emphasis on boosting those that have previously been vaccinated.”

But Lighter is optimistic that the worst of the pandemic is behind us as drugmakers like Pfizer and Merck are racing to put COVID-19 antiviral pills to use. “We're going to have these oral antivirals that are just going to change the whole trajectory of the pandemic,” she said.

Eventually, COVID-19 will become endemic, which means it will circulate like the seasonal flu, with smaller, more contained outbreaks, Oglesbee added. But the ability to achieve herd immunity in the U.S. would have been easier if vaccines were more widely accepted early on.

“I know it doesn't help to look in the rearview mirror, but the solution would have been when the vaccine rolled out, everybody stepped up and got vaccinated,” Oglesbee said. “The vaccine hesitancy that we're seeing in this very protracted approach now is really kind of changing the equation."

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.