With vaccinations underway, when can we expect to see herd immunity?

One of the goals of the nationwide COVID-19 vaccination effort is to achieve herd immunity.

When a significant portion of the population has immunity to a virus, either through a vaccine or by developing natural antibodies, the ability for it to spread is sharply limited.

So how many people in the United States would have to get vaccinated for that to happen? And how long would that take?

"The best case scenario for me is we get 85 percent of the people vaccinated by the end of the summer," said Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases. "If we do then by the time we get to the fall, we can approach a degree of normality."

To help reach that goal, the Biden administration recently agreed to buy an additional 200 million more doses from Pfizer and Moderna to be delivered this summer.

Cleveland Clinic infectious disease specialist Dr. Frank Esper says herd immunity happens when there's enough protection in the population to prevent continued spread of the virus.

"It's finding roadblocks because people are immune. And when the virus comes to you and you have immunity against it, that's a dead end for that virus. That virus has been blocked from spreading," Esper said.

He says getting vaccinated protects you and everyone in the community - including those who can't get the vaccine for medical reasons.

The number of people who need to be vaccinated to achieve herd immunity differs for each virus.

For coronavirus, Dr. Esper believes 70 to 90 percent of the population will need to be vaccinated, although scientists are still trying to determine exact numbers.

"As more and more people get that immunity, the spread of the virus is going to slow and slow. Eventually, we hope that it's going to get to the point where we get this herd immunity," Esper said.

It will be several months before we see large numbers of people within communities build up immunity to COVID-19. Experts like Esper and Fauci say one of the biggest barriers to this goal is getting those who are vaccine-hesitant on board.

"Many people are skeptical about that so we really need to do a lot of good outreach for that," Fauci said.

Vaccinated or not, health officials say basic preventative measures like universal masking, physical distancing and handwashing still remain essential.