![]() ![]() But as we build immunity to SARS-CoV-2, the risk of severe illness will decrease, and future waves of infection won’t be as disruptive. We should therefore expect to see some level of ongoing coronavirus transmission in our population for many years (if not forever). This means that we would need an even higher level of vaccination against COVID-19 to achieve herd immunity.įor all these reasons, it will be very challenging to get to the level of population immunity against COVID-19 that we have seen with measles in the U.S. People who have gotten vaccinated can still become infected (so-called breakthrough infections), and some people who have had COVID-19 can get it again. Third, while our vaccines against COVID-19 are very effective and dramatically reduce the risk of infection, they do not reduce that risk to zero. So, until we get vaccines that are approved for use in all ages, there is likely to be ongoing transmission of the coronavirus in kids, who will in turn be able to infect adults, especially unvaccinated ones. Second, young children are still not eligible for the vaccine, and new children (who are susceptible to COVID-19) are born every day. As of September 2021, just over half of the US population was fully vaccinated against COVID-19-even though we know that the FDA-approved vaccines are extremely safe and have remained highly effective, even against new variants like the delta variant. Yes-but “herd immunity to COVID-19” does not mean that we will soon achieve a level of immunity in the population, like what we see with measles, and coronavirus will be “over.” Returning to life as it was before the pandemic, without seeing large coronavirus outbreaks, is unlikely to happen for several years, for a few reasons.įirst, it has proven much harder to get people vaccinated against COVID-19 than against measles. Is herd immunity still an achievable goal for COVID-19? But even below any “herd immunity threshold,” immunity in the population (for example, from vaccination) can still have a positive effect by reducing the total number of infections that happen. Both viral evolution and changes in how people interact with each other can bring this number up or down as well. But this percentage isn’t a “magic threshold” that we need to cross-and it’s not just dependent on the level of population immunity. The more contagious an infection is, the higher the proportion of the population that needs immunity before infection rates start to decline. The hope is that the population can develop a high enough level of immunity to keep spread low. The same idea works for any infectious agent, including coronavirus. As a result, even though we still see localized outbreaks of measles in the U.S., those outbreaks generally die down without starting a nationwide epidemic. ![]() If a person with measles were to come to the U.S., for example, nine out every 10 people that person could infect would be immune, making it very hard for measles to spread in the population. This level of vaccination provides protection to the population as a whole-even to those who aren’t vaccinated-by decreasing viral circulation and the chance someone who is unvaccinated will encounter the virus. are vaccinated against measles, mumps, and rubella by their second birthday. ![]() When most of a population is immune to an infectious disease, this provides indirect protection-also called population immunity, herd immunity, or herd protection-to those who are not immune to the disease.įor example, currently over 90% of all children in the U.S. What do epidemiologists mean when they talk about “herd immunity”? In this Q&A, epidemiologists Gypsyamber D’Souza and David Dowdy explain that herd immunity is still possible for COVID-19, but that we might need to think a bit differently about what that means in this phase of the pandemic. With this changing perspective, how should we be thinking about herd immunity? As vaccination has rolled out, variants have emerged, and as cases surge once again, we are learning more about the nuances of SARS-CoV-2 infection and what short- and long-term immunity to this virus may look like. In the months following the emergence of SARS-CoV-2, “herd immunity” was frequently cited as the long-term destination of the COVID-19 pandemic. ![]()
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