The Full Story on Herd Immunity

A poorva Mandavilli of the New York Times offered up a heaping serving of dire pessimism on Monday morning, warning that despite the still-active U.S. vaccination effort, the country is unlikely to reach herd immunity anytime soon, if ever.

“Now, more than half of adults in the United States have been inoculated with at least one dose of a vaccine. But daily vaccination rates are slipping, and there is widespread consensus among scientists and public health experts that the herd immunity threshold is not attainable — at least not in the foreseeable future, and perhaps not ever,” Mandavilli wrote. “Early on, the target herd immunity threshold was estimated to be about 60 to 70 percent of the population. . . . Experts now calculate the herd immunity threshold to be at least 80 percent.”

First, while daily vaccination rates are indeed slipping, we’ve still averaged 2.4 million doses per day for the past week. A daily rate that’s lower than our peak doesn’t necessarily mean low. We didn’t hit that peak average of 3.37 million doses administered per day rate until March 5. The U.S. average doses administered per day is about 400,000 behind the combined European Union countries — compared with Europe, the U.S has a massive head start — and about 147,000 more per day than India. Would it be preferable if the U.S. stayed near its peak? Sure. But it’s not surprising that older Americans and those with health issues would be most eager to get vaccinated, and that younger and healthier populations would be less enthusiastic.

We should, and will, try to maximize vaccination among these younger and healthier populations. But remember that in some states, young, healthy adults only became eligible for vaccines in mid April, and the day you become eligible is not necessarily the day you can find an appointment or get a shot, although many sites now have no wait lists. Additionally, the Pfizer and Moderna vaccines require two doses, which means that young healthy Americans couldn’t get fully vaccinated with these vaccines until mid May.

The next thing to keep in mind is that herd immunity is not binary. It’s not as if there’s no protection to the rest of the population at 79.9 percent, but then at 80 percent everything changes.

Dr. Aileen Marty, an infectious-disease expert at Florida International University, described it to NBC News in March: “Herd immunity is not an on off switch. It’s more like a dimmer so that the further we get along, the better all of us are in terms of protection and in terms of getting back to normal.”

This virus, like all viruses, survives by jumping from body to body. The virus infects one body and then looks for opportunities to spread to new ones. The virus has to do this, because the host body will either generate enough antibodies to fight off the virus, or it will succumb to the virus and die. A virus needs to keep moving to live, and each day in the U.S., the virus gets a little less room to maneuver, between a combination of 105 million fully vaccinated people, 42 million partially vaccinated people, and a 33 million cases of past infection (a population that overlaps to some degree with the populations of the fully and partially vaccinated). Every day, we’re administering another 2 to 3 million doses into American arms, and every day SARS-CoV-2 is getting more and more boxed in.

You’re hearing a lot about variants. No one wants to whistle past the graveyard, but so far, the vaccines are beating the variants. The CDC is currently concerned about five of them.

Pfizer vaccine works against B.1.1.7 (commonly called the U.K. variant), B.1.351 (the South African variant), and P1 (the Brazilian variant). Moderna and Novavax are effective against B.1.427 and B.1.429, the two California variants.

We may very well need booster shots in the future to tackle future variants. The American Society for Microbiology concluded:

Studies indicate that the B.1.1.7 variant is, in fact, neutralized by antibodies developed in individuals who have been vaccinated with Pfizer and Moderna mRNA vaccines. Reduced neutralization potency against the B.1.351 variant has been observed. However, studies have shown that serum of mRNA vaccinated individuals is still able to fully neutralize the B.1.351 variant. And J&J, the 3rd vaccine to receive EUA in the U.S., has still shown high efficacy against severe disease in individuals infected by B.1.1.7 and B.1.351. In order to ensure maximum efficacy of its product, Moderna announced that it has launched a clinical program to develop vaccine boosters that will account for current and emerging SARS-CoV-2 variants, and Pfizer has recently followed suite.

So far, every variant is at least somewhat vulnerable to our vaccines. (Knock on wood.) And all of these numbers represent an effort without a vaccine for those under age 16 yet. This past weekend, former FDA commissioner Scott Gottlieb said on CBS’ Face the Nation: “I’m hopeful the FDA is going to authorize [a vaccine for teenagers] in a very short time period. And I think when — once that gets authorized, I think you’ll pick up probably 5 million kids [who] will get immediately vaccinated. There’s about 17 million children between the age of twelve and 15. I think we’ll pick up about 5 million immediately. I think probably another 5 million, 5 to 7 million would get vaccinated over the course of the summer before the school year.”

Deep into Mandavilli’s story, in the 28th paragraph, she acknowledges that as long as the vaccines work against the variants . . . it doesn’t matter that much if our population is 60 percent vaccinated or 80 percent vaccinated. If we’ve got our most vulnerable citizens vaccinated, and their immune systems are prepared to run into SARS-CoV-2 or any of its variants, we’ve greatly reduced the likelihood of the worst-case scenarios:

If the herd immunity threshold is not attainable, what matters most is the rate of hospitalizations and deaths after pandemic restrictions are relaxed, experts believe.

By focusing on vaccinating the most vulnerable, the United States has already brought those numbers down sharply. If the vaccination levels of that group continue to rise, the expectation is that over time the coronavirus may become seasonal, like the flu, and affect mostly the young and healthy.

We would like to vanquish COVID-19 completely; but we need to protect the most vulnerable. By and large, we’ve done that. Almost 70 percent of American senior citizens are fully vaccinated; almost 83 percent have at least one dose.

Gypsyamber D’Souza and David Dowdy, epidemiologists at the Johns Hopkins Bloomberg School of Public Health, concluded early last month:

Current projections are that we can get more than half of all American adults fully vaccinated by the end of Summer 2021 — which would take us a long way toward herd immunity, in only a few months. By the time winter comes around, hopefully enough of the population will be vaccinated to prevent another large surge like what we have seen this year.

Can we reach herd immunity? We can get close, which might just be close enough.