Vaccinating kids, however, is often not just about the direct and immediate benefits to them. It’s also meant to protect children against diseases that would otherwise become more dangerous for them as adults—measles, mumps, and chicken pox are three common examples—and dampen the overall spread of these diseases. In the short term, the primary reason to vaccinate children against COVID-19 may be that the U.S. will have a hard time reaching herd immunity otherwise.
Vaccines that work in adults generally work in children. But their effects can differ, especially in very young children. In newborns, for example, antibodies passed to them in utero can interfere with the protection conferred by the measles vaccine, which is why that vaccine is not given until babies are 12 to 15 months old. An early version of the pneumococcal vaccine did not work well in children under 2, because it stimulated a part of the immune system that was not yet mature.
Multiple factors determine the recommended age for a vaccination. “For example, when’s the peak incidence of disease? When is a child most likely to respond to the vaccine?” says Cody Meissner, an expert on pediatric infectious diseases at Tufts. The answers to those questions might not align. For instance, the vaccine for HPV, a sexually transmitted virus that can lead to cervical cancer, is given to boys and girls as young as 9 years old because it stimulates a better immune response in preteens than in older adolescents, even though preteens are unlikely to need the protection until later in life.
Even though kids rarely get seriously sick from COVID-19, the vaccine can protect them from an illness that may still be bad enough for them to miss school and their parents to miss work, Jeff Gerber, a pediatrician at Children’s Hospital of Philadelphia, told me. “Even those two-to-three-day illnesses can pile up.” He pointed out that the flu vaccine is recommended for kids, and about the same number of children died of the flu last season as have died of COVID-19 to date.
But the main argument for broadly vaccinating children is that doing so is likely to reduce COVID-19 transmission. Although schools have not been sources of large outbreaks, many switched to distance learning, and most of those that held in-person classes required masks and distancing. If school buildings reopen without these precautions sometime this year, after adults get vaccinated but while kids are still vulnerable, they will essentially be hosting mass gatherings of unvaccinated people, says Jason Newland, a pediatrician at Washington University. “Guess who’s going to end up having it? All the kids,” he told me. “And those kids with certain underlying conditions are disproportionately impacted.” What’s more, kids could bring COVID-19 home from school, even if they don’t have symptoms. “Children could pass it on to Grandma and Grandpa. They can pass it on to another loved one who has diabetes or has obesity or has chronic kidney disease” and is not yet vaccinated, Newland said.