CHICAGO (NewsNation Now) — More than a year after the COVID-19 pandemic first brought lockdowns, restrictions, mask mandates, and social distancing to the U.S., many are looking for signs of when things may return to normal.

One of these indicators is “herd immunity,” which many hold up as an ultimate goal for vaccination efforts in the country. But what does it mean, and could it ever be achieved in the U.S.?

What is ‘herd immunity’?

At the most basic level, immunity means a person is protected from a disease.

This typically occurs when our immune system generates antibodies after being exposed to a new virus known as natural immunity or vaccines.

But herd immunity is indirect protection that occurs when enough of the population or “herd” have antibodies to prevent the disease from spreading.

“So it’s really like having a barrier of people who are protected, who break that chain of transmission. So, you don’t need every single person in the area, in the population, to necessarily be protected,” according to World Health Organization Chief Scientist Dr. Soumya Swaminathan.

As the proportion of people with antibodies against a disease increases, the number of new infections in a community eventually begins to decline due to herd immunity.

Swaminathan points to efforts to combat measles as an example, which experts say is highly communicable and requires 95% of the population to have immunity to stamp it out.

“Even if you have 5% of children not vaccinated, these others actually have enough protection in the population to prevent the measles virus from actually going from one person to the next,” Swaminathan said.

In the U.S., smallpox and polio were eliminated as part of global vaccination programs, which continue to this day.

What do we know about COVID-19 and herd immunity?

Since COVID-19 is so new, experts don’t know definitively what percent of the population has to have antibodies for herd immunity to begin to make an impact.

This is further complicated by the emergence of more infectious variants, which would likely raise the threshold for herd immunity to be reached.

National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci previously said between 70% and 85% of people would need to be immune to contain COVID-19. However, he recently said he would stop discussing herd immunity because variants made it hard to estimate.

“I have never seen anything like this particular virus, in its complexity and its ability to elude what we’re trying to do to contain it,” said Fauci told the American Medical Association in February.

Immunologist Dr. Alessandro Sette told the Association of American Medical Colleges the 85% level seemed reasonable, although it could be lower.

For this to be achieved, between 230 million and 280 million Americans would need to have some form of immunity, according to the AAMC, which puts the current number of those with antibodies at about 182 million.

When will herd immunity allow the U.S. to fully reopen?

When it comes to COVID-19, conversations about herd immunity are usually about something else: when can life get back to normal?

At the start of the pandemic, many officials said measures meant to prevent the spread of the novel coronavirus would continue until herd immunity against the virus was reached.

While 247 million vaccine doses have been administered across the U.S., one factor slowing the pace of vaccinations is a large portion of the population still has to wait: children under 16 years old, including nearly 50 million kids under age 12.

Studies proving vaccines are safe for kids are still underway and will likely take months to complete.

The question has also become a political one. A poll conducted in late March found that 36% of Republicans said they would probably or definitely not get vaccinated, compared with 12% of Democrats. 

Some polls found as much as 30 percent of the U.S. population say they’re hesitant about getting vaccinated, according to The New York Times.

So while the country may be able to see enough vaccinations to significantly decrease the number of new infections, it seems unlikely COVID-19 will be fully stamped out in the U.S.

When asked about when the U.S. may achieve herd immunity Monday, President Joe Biden said there’s a dispute over what percent of the population needs to be vaccinated to achieve it.

In the end, when to fully reopen is up to each individual state, whether or not they have achieved herd immunity. Many states are choosing to lift COVID-19 restrictions as vaccinations continue and the number of cases continues to decline.

On Monday, Florida Gov. Ron DeSantis moved to suspend all remaining COVID-19 restrictions imposed by communities across his state.