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Will we ever reach herd immunity?

More contagious variants of COVID-19 may push herd immunity out of reach, but vaccines remove the virus’s sting

Photo by Sanjay Kanojia/AFP via Getty Images

Will we ever reach herd immunity?

Since the beginning of the COVID-19 pandemic, health officials, government leaders, and media reports have discussed reaching herd immunity—when enough people have become immune to a virus (either by vaccination or natural infection) that the virus can’t meaningfully spread.

Some countries seemed to be approaching herd immunity by the end of this summer. In the United Kingdom, for example, 81 percent of the population age 16 and up had been vaccinated as of mid-September.

Yet as the virus mutates, new variants may put that goal out of reach. Even with its high vaccination rate, the U.K. continued to see high numbers of new COVID-19 cases.

We take herd immunity for granted with diseases like measles: In the United States, when outbreaks do start (typically via someone who has traveled from a country where it remains endemic), they spread through a small number of unvaccinated people before fizzling out. “Large” outbreaks are measured in the hundreds of cases, and no American is known to have died from measles since 2015. This makes sense, because 92 percent of Americans have received the measles vaccine.

Early in the pandemic, some people hypothesized that the threshold for herd immunity to COVID-19 might be much lower, with the Swedish ambassador to America predicting the United States would reach herd immunity as early as May 2020. Those hypotheses continued through last year, with our coverage from September 2020 noting that estimates for the herd immunity threshold ranged from 20 percent to 70 percent. All of those, however, predated the virus’s more-contagious delta variant.

Delta transmits more easily between people: An August study in the Journal of Travel Medicine found that it roughly doubles infectivity compared with the original strain. Second, Nature reports that during an outbreak in southern China, almost three-fourths of delta transmissions appeared to happen before symptom onset. In other words, before a person began to feel sick and knew to stay home, he or she could have passed the virus on.

Vaccines also appear to be less effective in preventing minor infections from the delta variant, which may be enough to pass COVID-19 on to others. Over time, even vaccinated people and those who had previously contracted the coronavirus may begin to lose their immunity. This has given rise to debates about whether the COVID-19 vaccines should join the list of vaccines needing three—or more—shots. (For instance, the diphtheria-tetanus-pertussis vaccine involves a series of five doses, and the polio vaccine involves four.)

Will we reach herd immunity, then, with COVID-19? Sir Andrew Pollard, who heads the Oxford Vaccine Group, says no: He told the British All-Party Parliamentary Group (APPG) in August that “this current variant, the delta variant, will still infect people who have been vaccinated and that does mean that anyone who is still unvaccinated at some point will meet the virus.”

The participants in the APPG forum emphasized vaccines still protect their recipients: While the shots don’t reliably prevent mild cases of the delta variant, they remain strong against more severe infections. This might sound odd, but it makes sense: A vaccine’s goal is to teach the immune system to recognize a given invader and make antibodies quickly. An invader that moves more quickly might get a foothold—that’s the mild infection—but ramping up antibody production without delay can prevent that mild infection from becoming serious. This makes a major difference: A Public Health England study found the vaccines continued to offer excellent protection against hospitalization, including from the delta variant. (That explains why the vast majority of hospitalized patients in the current COVID-19 wave are unvaccinated.)

Evidence now points to the virus becoming a permanent, rather than temporary, part of our lives—albeit with variants raising the stakes for people who avoid vaccines. Pollard may be correct that we will fall short of true herd immunity, but it isn’t a binary all-or-nothing phenomenon. Each person who receives a vaccine before exposure, each person who doesn’t get sick after exposure, and each person who gets a mild case instead of more severe case of COVID-19, represents one more step toward the end of the public health emergency.

Charles Horton, M.D. Charles is WORLD's medical correspondent. He is a World Journalism Institute graduate and a physician. Charles resides near Pittsburgh with his wife and four children.


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Dr. Horton, thank you for this and thank you for sharing more than just an opinion, but facts and research from respected and credible sources. The key take away if we ever want to move on from the pandemic (and those refusing to do what you note here are not only prolonging the effects of the pandemic, mask wearing, distancing, the toll on business/travel, etc., they are harming their neighbor), is as you note:

"Pollard may be correct that we will fall short of true herd immunity, but it isn’t a binary all-or-nothing phenomenon. Each person who receives a vaccine before exposure, each person who doesn’t get sick after exposure, and each person who gets a mild case instead of more severe case of COVID-19, represents one more step toward the end of the public health emergency."

Again, thank you for sticking with facts, science, and actual research and not spreading health misinformation, lies, and conspiracy theories. One is 10-11 times more likely to die from Covid if not vaccinated. The vast consensus of medical doctors, immunologists, and medical researchers, in America and world-wide, agree the vaccines work. See: https://www.mcgill.ca/oss/article/covid-19-health/how-we-know-covid-19-vaccines-work

When it comes to a pandemic, misinformation kills.


I am truly disappointed by this article that is not showing true data. For example what is driving the variants? You can look at the graphs for the most highly vaccinated countries, on the John’s Hopkins COVID tracking website and see that cases were way down before the administration of the vaccine in Britain, Israel, and Gibraltar, and immediately after administration Covid cases shot up to the highest levels recorded. I think there is also an issue with reporting what is categorized as “unvaccinated”. In most cases people with one dose are categorized as “unvaccinated” as are those within 14 days of the 2nd dose. These are truly disturbing facts that correspond to the data being reported but not being examined critically. Thank goodness for millions of scientists who are researchers, data crunchers and see through these tactics. We live in a new era where even reporters must do greater diligence. A true vaccine does NOT lessen the symptoms. It’s disingenuous to continue to advance this “narrative”. The vaccines don’t work. Please answer these questions with the next article.

Todd Erickson

No data, just an opinion. This is not helpful for the discussion that needs to happen regarding individual health, which will lead us closer to the ever elusive herd immunity. Please apply the principles of science to your writing - present data and allow everything to be questioned.


I believe Dr. Cole is also an immunologist. There is certainly a benefit to objectively considering all credible evidence before making a final assessment. I found the 30 minute interview of Dr. Cole very informative in my quest to search out what is the best path for me.


Dr. Ryan Cole, an epidemiologist in Idaho, has a video that is getting widely circulated that has raised concerns about the effect of the vaccines on naturally occurring autoimmunity, especially in young children. Open dialog on the potential long term implications of how we address this pandemic are critical.

Laura WWayne52

I'd rather hear from someone who deals with auto-immune diseases. Epidemiologists study contagious diseases and how they spread in a population, which isn't really related to the concern voiced.