Vaccines Pave the Path to Herd Immunity

How long will it take for enough people to become immune to COVID-19 that it makes the spread of the disease unlikely?

Feb. 2, 2021

herd immunity

As the pandemic continues, people are wondering even more about the possibility of herd immunity—or, the point at which enough people in a community are immune to COVID-19 so it makes the spread of disease unlikely. Now that the coronavirus vaccines are being distributed in the Rochester community, some might wonder:

“Can the vaccines move us closer to herd immunity sooner, rather than later?”

That depends.

The number of people vaccinated

First, just to compare, let’s consider what would happen if the vaccines were never developed.

In that case, it would mean that in the U.S., 70% of the population (more than 200 million people) would have to recover from COVID-19 to end the pandemic. If that many people became sick with COVID-19 at once, our health systems would quickly become overwhelmed and the amount of infection could lead to a large number of deaths. It would take until May 2025 to possibly achieve “natural” herd immunity. That’s just over four years away.

Rochester Regional Health infectious disease specialist Dr. Emil Lesho isn’t losing hope yet.

“The good news is that we do have two currently approved vaccines that are more than 94% effective in preventing COVID-19 infection,” says Dr. Lesho.

While the Centers for Disease Control and scientists around the world are still studying herd immunity and the exact percentage vaccinated we'd need to hit in order to end the pandemic, some, like Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, are hopeful that if a high percentage of the population is vaccinated by the end of the summer, then we may reach enough herd immunity to protect our society from COVID-19 by the end of the year. 

How are these timeframes calculated?

Herd immunity, and how long it could take for us to get there, can be determined by using three pieces of information:

Basis reproduction (RO) which is how quickly the virus can spread.

Base prevalence is the percentage of people who have immunity, or received the vaccine.

Monthly infection rate is the percentage of people, who become infected and then become immune. It’s important to keep in mind that it’s still unclear whether this is true or not for people who have had COVID-19.    

“Using this information, we can calculate the number of people who need to become immune to COVID-19 in order to stop it from spreading,” says Dr. Lesho. “With that number, it’s possible to determine the number of months it will take to get there based on peoples’ willingness to get the vaccine.”

Do we need a vaccine to reach herd immunity?

Historically, herd immunity has only been reached through the use of vaccines. Think about polio, smallpox, and measles—we don’t we don’t have to worry about these diseases because most people have been vaccinated.

Although there are still unanswered questions about the vaccines, some that only time can answer. But they can help us return to “normal” sooner than later. And, it’s important to keep in mind that getting the COVID-19 vaccine protects those who get the vaccine, and prevent the virus from spreading to others who can’t get vaccinated.

Whether people choose to get the vaccine or not, we still need to continue to do our part to help stop the spread of COVID-19. Social distancing, hand hygiene, and face coverings will be around for a while. But for how long is up to us.