Can COVID-19 herd immunity be reached without vaccinating kids? It’s complicated

Amid a race to vaccinate as many people as possible against SARS-CoV-2, the virus that causes COVID-19, which has sickened more than 28 million people and killed about 500,000 in the U.S., the 10-year-old son of a Washington Post reader posed a pertinent question, one even experts are struggling to answer with any real certainty.

Is it possible for the U.S. to achieve herd immunity without vaccinating children?

It’s a complicated question, as health experts have differing ideas about what constitutes a herd immunity threshold for the coronavirus. Add to that the challenges with virus mutations, vaccine hesitancy and, of course, the current inability to vaccinate children, and the answer becomes even murkier.

It makes herd immunity a challenging target to hit even assuming adults and children took the vaccine. Without vaccinating children, it makes it that much more difficult. But failure to reach that threshold does not mean failure to control the disease.

What is herd immunity?

Herd immunity occurs when a large number of people in the community have developed immunity either by getting infected or by being vaccinated, so they are less likely to spread infection.

The herd immunity threshold refers to the level of herd immunity needed so that when people return to their normal pre-COVID-19 lives, transmission of the virus cannot be sustained. That does not mean that the virus will completely disappear, but it will spread only among certain individuals rather than among the community at large, preventing new outbreaks, said Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health.

For COVID-19, the herd immunity threshold is thought to be between 70% and 90% of the population.

It is possible to reach herd immunity without vaccinating kids?

No one really knows.

Assuming almost all adults got vaccinated, it could be possible to curb the spread of infection among the adult population.

However, children would continue to pass on the virus to their peers “until community rates are low enough that children are no longer getting infected,” said Stuart Ray, a professor of medicine in the division of infectious diseases at Johns Hopkins University. “Then what we might see are occasional sporadic outbreaks among children who are connected by transmission roots.”

As it stands, about half of unvaccinated adults surveyed in the U.S. said they “definitely” intend to take the vaccine, but 14% said they would “probably not” and 10% gave a resounding no, according to census data released last month.

If children – who account for about 22% of the U.S. population – also were not vaccinated, herd immunity would be even further out of reach. However, hitting the threshold is not a pass-fail mission. Some experts believe that the threshold is more of a spectrum, and the closer the population can get to it, the better the chances of stopping the spread of the disease.

The rationale behind vaccinating children, experts say, is not only to help the entire community reach herd immunity but also to protect kids from COVID-19. Although, in general, the virus has been much kinder to children than adults, not all children have been immune to some of the associated health risks, particularly multisystem inflammatory syndrome in children.

Federal health authorities have warned parents about MIS-C, in which “different body parts can become inflamed, including the heart, lungs, kidneys, brain, skin, eyes or gastrointestinal organs.” Most kids who have been diagnosed with the condition after developing COVID-19 have recovered, though the illness can be fatal, according to the Centers for Disease Control and Prevention.

Furthermore, Ray said, experts do not know how the virus may affect children and their development down the line. “I don’t think we can exclude that there will be late complications we just haven’t thought of yet.”

“That’s the reason we would like to be able to vaccinate children,” he added.

So why aren’t we vaccinating children?

The Pfizer-BioNTech vaccine is permitted for use in teenagers as young as 16. Both Moderna and Pfizer-BioNTech are running clinical trials testing the vaccine in children ages 12 and older.

Anthony Fauci, the country’s leading infectious-disease expert, said during a White House briefing last month that assuming the trials are successful, they will be opened to children as young as 9. He said vaccines could be available to children beginning by the late spring or early summer.

Even so, if it is not possible to reach herd immunity, Lipsitch said, he is not “despairing.”

Because, with vaccination, “I think we can solve the biggest problem with the pandemic, which is the toll on the health care system and the toll on human life without reaching the herd immunity threshold,” he said.

The Washington Post’s William Wan contributed to this report.