Nearly half US might have ‘natural immunity’ from COVID-19, but infection brings high risks

A viral image shares a statistic that suggests that the United States has reached a point where it can manage the COVID-19 pandemic with less reliance on vaccines.

"Nearly ½ of the United States population has Natural Immunity to Covid," the image stated. 

The post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

It’s not possible to know exactly what percentage of the United States population has some level of natural immunity attributable to becoming infected without having been vaccinated. That’s because not all infections get recorded, since some people who were infected didn’t know it, or had symptoms but never got tested.

Moreover, natural immunity is not absolute — protection decreases over time — and people who are unvaccinated and become infected are at a much higher risk of hospitalization or death. 

The term natural immunity "makes it sound superior when it’s not superior," said infectious disease epidemiologist Josh Michaud, associate director for global health policy at Kaiser Family Foundation. "So many people have died in the process of acquiring so-called natural immunity."

We're not rating this claim, but we wanted to shed more light on the accuracy of statistic and what it misses.

The Facebook user who shared the image on Oct. 5 cited the New York Times’ morning newsletter from the previous day. 

The newsletter made one reference to natural immunity, saying: 

"The share of Americans 12 and over who have received at least one vaccine shot has reached 76%, and the growing number of vaccine mandates — along with the likely authorization of the Pfizer vaccine for children ages 5 to 11 — will increase the number of vaccinations this fall. Almost as important, something like one-half of Americans have probably had the Covid virus already, giving them some natural immunity."

It’s possible that nearly half the population has some level of natural immunity, but estimates vary.

• Georgia Tech researchers, using COVID-19 case estimates from the U.S. Centers for Disease Control and Prevention, estimate that as of Oct. 9, 52% of the U.S. population had been infected. But that figure includes vaccinated as well as unvaccinated people.

• Dr. Eric Topol, director and founder of the Scripps Research Translational Institute, told PolitiFact he estimates that 40% of the U.S. population has natural immunity.

• A study led by a Yale University researcher estimated that as of July 15, nearly 115 million people in the U.S. had been infected. That would be about 35% of the total U.S. population of nearly 333 million. The estimate was based in part on infection-fatality data from the CDC.  As of July 15, "the U.S. population immunity against COVID-19 may still have been insufficient to contain the outbreaks and safely revert to pre-pandemic social behavior," that study concluded.

• A study led by a CDC researcher examined 1.44 million blood donations from July 2020 through May 2021 and then made estimates that account for differences between the blood donors and the U.S. population. The study estimated that as of May 2021, 20% of the U.S. population had antibodies that their immune systems produced in response to a COVID-19 infection. 

The exact percentage of how many people in the United States have been infected is not known because it’s not possible to count cases that were never reported — people who were infected and didn’t know it and those who had symptoms but didn’t get tested.

"Nearly half is within the realm of possibility, but nobody knows for sure and it’s impossible to know," Michaud said. "There’s a lot of undercounting of infections."

While the statistic itself may be in the ballpark of what researchers have found, there’s a lot more to know about what natural immunity does and doesn’t mean.

Level of protection from natural immunity: We rated Mostly True a claim that people who "have recovered (from COVID-19) have very strong immunity." A study in Israel published in August found that natural immunity gives longer lasting and stronger protection than the Pfizer vaccine. 

But a study published in August by the CDC found that among people in Kentucky who had been infected in 2020, the unvaccinated were 2.34 times more likely to become reinfected than those who had been vaccinated.

"Individuals who have had disease do have some protection against infection, but vaccination provides a significant benefit above and beyond immunity that is conferred by having COVID-19 disease," said Dr. Matthew Laurens, of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine.

Broader protection with vaccine: A claim that "it makes no sense to require vaccinations for the previously infected," received a False rating. While people who have had COVID-19 do have some level of immunity, at least against the strain they were infected with, the CDC recommends vaccination because it provides better protection. It’s not clear how long natural immunity lasts and it may not be as effective against variant strains of the virus. There is also evidence that unvaccinated people who get COVID-19 are more likely to spread the virus than vaccinated people who get the virus.

Experts disagree on how much protection an infection delivers.

Cindy Prins, clinical associate professor of epidemiology at the University of Florida, said the two-dose Pfizer and Moderna vaccines give the body’s immune system a better chance to fight off infection.

"We don't know for certain how long either natural immunity or" immunity from vaccines last, "but the mRNA vaccine two-dose series offers more than one opportunity for the immune system to recognize the spike protein and respond to it, and now additional boosters are being made available to people," she said. 

Since the level of infection varies among individuals, so does the protection. Variants can pose a greater risk to individuals than the version of the coronavirus they were infected with, said Michaud. "Natural immunity is less predictable than vaccine-induced immunity," he said.

Unvaccinated face higher risks: We rated False a claim that it’s safer to be unvaccinated than vaccinated against COVID-19. 

In September, the CDC analyzed vaccine effectiveness across 13 jurisdictions from April 4 to July 17 and matched that data to vaccine registries from those areas. It found that after delta became the most dominant variant, unvaccinated people were five times more likely to be infected than fully vaccinated people, and more than 10 times more likely to be hospitalized or die. 

Meanwhile, there is no clear evidence that the COVID-19 vaccines have caused any deaths in the U.S.

"To become naturally immune, you have to go through the gauntlet of an infection, and that is a much higher risk gauntlet than being vaccinated," Michaud said.