Recent reports of vaccinated people being diagnosed with COVID-19 have caused alarm in places like Michigan, where a headline blared: “246 vaccinated residents diagnosed with COVID; 3 dead.” Breakthrough infections—cases where the coronavirus takes hold in a fully inoculated person—will always raise worries about whether the vaccines are actually working. And more than 200 incidents in a place where the variants are surging? Yikes.
But without the appropriate context, statistics can breed misconceptions or even deceive. When that headline ran, the total number of fully vaccinated Michiganders at the time was approximately 1.5 million. Recording 246 breakthrough infections among this enormous group would mean the COVID vaccines are actually performing better than expected relative to their clinical trial results. Even The Washington Post reporting “several thousand” of these cases across the United States should not raise doubts about the vaccines’ efficacy.
“The numbers indicate clearly that the vaccine is having a substantial effect,” says Jeffrey Shaman, an epidemiologist at Columbia University's Mailman School of Public Health. “People just need to reorient themselves and get it in their mind that it is not 100%.”
Breakthrough infections can undoubtedly come with serious consequences, and city and state health officials are on alert for them. A spokesperson for the New York City health department told Gothamist/WNYC that they’re actively analyzing this situation, but for now, none of their evidence suggests the original strain of the virus nor its variants are bypassing the vaccines.
Those words were echoed by their counterparts in New Jersey and on New York State’s health team in Albany.
“While there are anecdotal reports of New Yorkers who have had a positive COVID test 14 or more days after receiving their last vaccine dose, DOH is investigating these cases further to determine if they meet the formal CDC definition of vaccine breakthrough,” New York State Health Department spokesperson Jill Montag wrote in an email.
So while we wait for more numbers to arrive, let’s take a brief refresher on what’s known about the effectiveness of the COVID-19 vaccines—and why thousands of breakthrough infections still mean those drugs are way more likely to protect you than not.
How Many Breakthrough Infections Should We Expect?
A vaccine can do three things. Best-case scenario: It stops a person from ever being infected. Alternatively, some vaccines can prevent a person who catches the coronavirus from transmitting it onward to someone else. Or the drugs might only stop symptoms, preventing a germ from wrecking your body.
Last spring, when drug companies and universities announced their intentions to make coronavirus vaccines, health regulators asked them to prioritize the third. Stopping COVID-19’s severe outcomes—the lung damage, the self-attacking meltdown of the immune system and death—seem like obvious priorities. But symptoms are also way simpler for scientists to track relative to infection rates, especially since 30% of coronavirus cases are asymptomatic.
“That's the thing that they can observe easily,” Shaman said. “If you have symptoms, they swab you, they find out who has COVID, and they compare the numbers in the group that got the actual vaccine versus the placebo.”
That’s why public messaging has focused on how the COVID-19 vaccines fared against severe disease. Pfizer-BioNTech, Moderna, and Johnson & Johnson vaccines performed equally well in clinical trials—about 10% given the shot developed severe COVID, and none died from the virus.
Focusing on severe disease is valuable, but it’s a bit like only counting home runs toward your team’s baseball score. What about the times that people struck out—and still caught the virus?
Scientists would predict one COVID case for every 2,000 people who take both shots of Moderna or Pfizer.
When it came to preventing any case from happening, whether mild or severe, the Pfizer and Moderna vaccines had 95% efficacy—but that doesn’t mean 5% of inoculated people will get infected. You have to factor in the virus’s attack rate—or the likelihood of getting sick after exposure.
After you do that, scientists would predict one coronavirus case for every 2,000 people who take both shots of Moderna or Pfizer. For Johnson and Johnson's single-shot, it would be about one in 300.
“Even with that 95% number, which is pretty darn fantastic, you still have a chance of being asymptomatic, a confirmed case, winding up in the hospital or even dying,” Shaman said.
Compare that against the numbers from Michigan of 246 breakthrough infections out of 1.8 million shots—that’s a much lower rate of one coronavirus case per 10,000 vaccinated.
“If you look at deaths, three people who had the vaccine have died. Four thousand Michiganders died since January 1st [of COVID-19]—Again, less than one in a thousand.” Shaman said. “The numbers that we're seeing there [in Michigan] are not out of the bounds of what you would expect and may be better, even.”
Evidence shows the coronavirus vaccines are squashing cases and deaths. Health researchers in countries like Israel and the UK are reporting they may have reached the herd immunity threshold, the point at which so many people are immune that the coronavirus stops spreading. Across the tri-state area and the U.S., cases and hospitalizations have plummeted in vaccine prioritized groups such as those in nursing homes and adults older than 65.
But even if the COVID-19 shots protect 1,999 out of 2,000 takers (or 9,999 out of 10,000), no one wants to be the odd person out.
Who Gets Breakthrough Infections And Are They Worse Off?
Breakthrough infections happen with all vaccines, including the best-performing ones for diseases like the measles. When media outlets like the New York Post run back-to-back-to-back stories on breakthrough infections, it can make the issue seem more problematic than it actually is.
“There’s primary vaccine failure, when the body actually doesn’t mount an adequate immune response for a number of reasons,” White House chief medical advisor Dr. Anthony Fauci said Monday at a COVID-19 Task Force briefing. “Secondary vaccine failure may occur when immunity fades over time...however, even if a vaccine fails to protect against infection, it often protects against serious disease.”
The clinical trials for the COVID-19 vaccines recruited large and demographically representative groups of volunteers in order to mimic how the drugs might perform in the real world. But even then, those tests can only give a rough prediction of what might happen.
“You're talking about a particular setting and a situation where everything is very well controlled,” said Bruce Y. Lee, a public health policy expert at the City University of New York and executive director of Public Health Informatics, Computational, and Operations Research. “There's a decent likelihood that the people who choose to be part of a clinical trial are the ones who are more aware of the virus and may be more careful in general.”
That’s because someone who doesn't believe the virus is a problem is probably going to skip signing up to be part of a clinical trial. There is also the so-called Hawthorne effect, wherein people change their behavior and become self-conscious merely because they know they’re being studied. Lee says both trends can affect how often a volunteer encountered people with the coronavirus during a clinical trial.
Exposure is one of the key factors that decides whether you will catch a germ, even after you’ve been vaccinated.
And exposure is one of the key factors that decides whether you will catch a germ, even after you’ve been vaccinated. That’s because your body’s immunity works like the deflector shields in Star Wars. Get hit once with a small bump of virus particles, and your spaceship will survive. But bombard your nose and mouth with too much virus over a short period of time, and you’re more likely to get infected.
“If you're a health care worker and you are exposed to people who are shedding large amounts of virus in the hospital, you're getting a lot bigger exposure than someone who is being very careful, social distancing and making sure that people around him or her are wearing masks.”
The real-world effectiveness will typically be messier than a lab trial because of other variables, too, Lee said. Maybe your vaccine provider’s freezer is slightly warmer than it should be on the day of your appointment, so your shot loses a smidge of potency? Maybe the nurse doesn’t suck up every last drop into the syringe?
That’s why Shaman, Lee, the CDC and other public health experts are urging vaccinated people to keep following guidelines when they’re around big crowds of strangers. Even though the chances of catching the coronavirus are supremely reduced, the odds aren’t zero.
Real-world investigations also take time to conduct, and we’re still awaiting effectiveness results on the Johnson & Johnson jab. But so far, international studies of the Pfizer and Moderna vaccines show that they're also about 90% effective against coronavirus infections among the general public.
The sole exception involved a large group of nursing home residents in Denmark who witnessed only 64% protection. What gives? Well, the median age of these long-term care residents was 84 years old, which hints at another defining attribute of human immune systems: Your individuality.
“Protection derived from the vaccine is dependent on your immune response,” Lee says. “Most older adults sometimes don't get enough of a response from the flu vaccine, so that's why they introduced things like higher-dose flu vaccines.”
In clinical trials against COVID-19, vaccine efficacy dropped by 20 or so percentage points in people with cancer, who are more likely to be dealing with immunosuppression.
“If you're taking steroids or taking immunosuppressive medications or if you have chronic medical conditions—all of those may potentially may reduce your immune response,” Lee said. “There's [sic] questions about whether people with high body mass index may have less of a response to vaccine as well."
When Can We Stop Wearing These Dang Masks?
Everyone wants this pandemic to be over. In the U.S. alone, we’ve lost more than 550,000 friends, fathers, mothers, brothers, sisters, daughters, sons and cousins in a little over a year. Many of us have been stuck mostly inside for just as long. Spring is here. The vaccines are here. We’re ready for the country to fully reopen and turn into the rave scene from The Matrix (though preferably above ground in the sunshine).
Breakthrough infections are the reason why the safest move is still to wear a mask, socially distance and use good hygiene when in public or traveling—even if you’re vaccinated. While you’re highly unlikely to get sick, there is the small chance that you might catch the virus and spread it to people who haven’t received shots.
“We need to keep that up until we've really throttled the virus and reduced the case numbers in the community enormously,” Shaman said, while explaining why people still need to wear masks and avoid getting together in large crowds until the nation hits herd immunity. “We’re at 50,000 cases a day in the U.S. It would be a lot better if we were like 500 or 600.”
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