Mandy Armitage, MDMandy Armitage, MD, is a physician and medical writer with special interest in healthcare technology and education. January 21, 2021, 1:58PM (PT)
- Several different factors contribute to a community’s ability to reach herd immunity.
- Experts don’t know yet how many people need immunity to achieve herd immunity or how long it will take to get there.
- Herd immunity and “back to normal” life depend on everyone getting the vaccine as soon as possible.
With the recent emergency use approval of COVID-19 vaccines, there has been renewed interest in herd immunity. It’s a term you’ve probably seen and heard a lot of lately, but what does it mean? Will we achieve it in the U.S. — and if so, when?
Here’s a quick breakdown of what’s in store.
What is herd immunity?
According to experts, herd immunity is a term used to describe the slowing of disease spread that occurs “when a significant portion of a population becomes immune to an infectious disease.” Herd immunity limits the spread of disease. It can protect people in a community who are not immune if enough individuals are immune to the infection. This means that if enough people in your community either got COVID-19 and recovered or received a vaccine against it, it could protect the people who are unable to get the vaccine (due to medical conditions, for example).
Immunity can come from previous infection or vaccination. But experts prefer to achieve herd immunity through vaccination rather than infection. Vaccination helps avoid unnecessary illnesses and death that could otherwise happen if people become infected.
What percentage of the population needs to get vaccinated to have herd immunity to COVID-19?
The percentage of people who need to have immunity for herd immunity to work depends on the disease. In other words, it’s a different percentage for each infectious disease. That’s because not all infectious diseases are equally contagious. For example, measles is highly contagious, requiring around 95% of the population to be vaccinated before herd immunity is reached.
It’s also different for each community. Interventions such as wearing masks and eliminating large group gatherings can decrease the spread of the coronavirus, and there’s a lot of variability in how well communities are doing these things. It’s reasonable to think that the threshold percentage for herd immunity against COVID-19 could vary by where you live.
It should also be noted that experts still aren’t sure how long immunity lasts, either from infection or the vaccine. Data collection from the vaccine studies is ongoing, so that information will be available eventually, but it’s a big unknown right now.
How long will it take to reach herd immunity in the U.S.?
Again, this depends on a lot of things. Perhaps most importantly, it depends on how willing the public is to get vaccinated and how quickly it can be done. That said, Dr. Fauci estimated in December that we could get there by the fall of 2021. However, new strains of the virus could change that (see below).
What are the obstacles to reaching herd immunity in the U.S.?
Clearly, vaccines are the critical part of reaching herd immunity. But if the public is not convinced, we may not achieve herd immunity at all. And if vaccine rollout continues to be painfully slow, it’s going to take much longer to get there.
Also, new strains of the virus continue to surface. Recently, a new strain, which appears to be more infectious, emerged in the U.K. and has since found its way to the U.S. Additional strains have popped up in Brazil and South Africa, causing more concern. Fortunately, none of them appear to be resistant to vaccines at this point. But they are causing experts to be less hopeful about a return to “normal” activities later this year. A more infectious virus means it will be more difficult to contain.
Will life go back to ‘normal’ after herd immunity is achieved?
This virus has spread around the globe, is incredibly infectious, and continues to change. For these reasons, experts believe it’s unlikely that the virus will be eradicated. In other words, COVID-19 probably won’t “disappear,” as some people had hoped. But if it’s controlled, it could become a milder disease.
That’s why it’s so important to vaccinate as many people as possible. Slowing the spread of the virus — and staying on top of it with testing and contact tracing — is what needs to happen in order for restrictions to be lifted.
Because we don’t know how long immunity lasts, as mentioned before, vaccine boosters could be necessary. This could be similar to how we get a flu shot every year or a tetanus shot every 10 years. The good news is that the more people who get (and remain) vaccinated, there will be less risk involved, and we can start to live with fewer restrictions.
What can I do to reduce the risk of contracting or spreading the COVID-19 virus in the meantime?
Masks, social distancing, and good hygiene. You might be sick of hearing about it, but this is what needs to be done to reduce your risk of getting and spreading the virus. This also applies to those who have already had COVID-19 and recovered from it. Repeat infections are rare but possible.
The bottom line
Herd immunity takes into account several different factors, including:
- How infectious the disease is
- How effective the vaccine is
- How quickly everyone gets vaccinated
- How long immunity lasts
Experts don’t have all the answers yet. That’s why it’s difficult at this point to nail down a specific percentage for herd immunity and when it might happen in the U.S.