Vaccination safety

What is the safety data for the vaccine?

By far the most widely used vaccines in children are ones based on mRNA, offered in close to 90% of the countries and regions that have approved vaccines for kids, according to an analysis prepared for Nature by the health-analytics firm Airfinity. The mRNA vaccines “are really safe vaccines for everybody, including children,” says Kawsar Talaat, an infectious-disease physician and vaccine scientist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Md. Given to millions of adults before being used in children, they have an “unparalleled” safety record, she says.

Vaccine reactions (short-term reactions)

The short-term risks of the vaccine for children are very minimal. We need more research and the passage of time before we’ll fully know the long-term risk, but for other vaccines, it is well understood that the great majority of so-called long-term risks occur within the first 6 months.

There were slightly more negative reactions for children after their second dose compared with the first, but fortunately, these were very minimal. Myocarditis is a good proof of principle of the balance between risk and benefit for children: The risk of COVID-induced myocarditis is far greater than the risk of vaccine-related myocarditis (see more information below).

Evidence from research. Near–real-time assessment is essential to monitor health outcomes post-vaccination. In a recent study, 20 health outcomes were carefully selected through clinical consultation and literature review. Notably, results for these 20 health outcomes in the pediatric population provide reassuring real-world evidence of the safety of the COVID-19 vaccine in children and adolescents.

A total of 5,901,825 doses of the BNT162b2 COVID-19 vaccine were administered to 3,017,352 children ages 5 to 17 years enrolled in three U.S. commercial health plans between 2020 and 2022. Vaccine-related side effects were exceedingly rare. The most common serious side effect was myocarditis (see more information below), which had an incidence of 39.4 cases per million doses administered in children ages 5 to 17 years within 7 days after BNT162b2 COVID-19 vaccination.

In another study, during November 3–December 19, 2021, V-safe (a CDC safety monitoring system that allows users to share how they felt after getting a COVID-19 vaccine) enrolled 42,504 children ages 5 to 11 years who received a Pfizer-BioNTech COVID-19 vaccine; second dose information was available for 29,899 (70.3%) of these children.

During the week after dose 1, reactions at the injection site (54.8%; 23,290) and systemic reactions (34.7%; 14,734) were frequently reported; systemic reactions were more frequently reported during the week after dose 2 (40.9%; 12,223) than dose 1. Reactions were reported most frequently on the day after vaccination for both doses. The most frequently reported reactions after either dose were injection site pain, fatigue, and headache. Fever was more frequently reported after dose 2 (13.4%; 4,001) than dose 1 (7.9%; 3,350).

Approximately 5.1% of parents reported that their child was unable to perform normal daily activities on the day after receipt of dose 1, and 7.4% after receipt of dose 2. Approximately 1% of parents reported seeking medical care in the week after vaccination; most medical care was received via a clinic appointment (0.6%; 441).

Additionally, in a study conducted between January and June 2022 to test reactions to the COVID-19 vaccine in children, among young children (under age 5), reactive events were rare and mostly mild to moderate, with no serious reactions. Rates of fever were between 5% and 7%.

Myocarditis and myopericarditis

Some people, especially boys and men ages 16 to 24, develop inflammation of the heart muscle and its outer lining—conditions known as myocarditis and pericarditis—after receiving the mRNA vaccines. But those cases are rare, generally mild, and usually resolve on their own. In fact, side effects from the vaccines, such as headaches and fever, have mostly been mild in young children.

One study found myocarditis in 70.7 and 105.9 cases per million doses of Pfizer‐BioNTech vaccine in ages 12 to 15 and ages 16 to 17, respectively, or about 1 case per 14,000 vaccinations. Case studies indicate that the great majority of these cases resolve within the first 48 hours.

Another study found that the risk of myocarditis for children under 16 years is 37 times higher for those infected with COVID-19 than those who haven’t been infected with the virus. Overall, for children, the risk is an estimated 146/100,000 among those with COVID-19.

An analysis of studies from around the world that included hundreds of patients between 12 and 20 years old who had no history of myopericarditis (a combination of myocarditis and pericarditis) or heart disease (most were males around 16 years old) found that myopericarditis after being vaccinated for COVID-19 was also extremely rare. Myopericarditis was seen more often after the second COVID-19 vaccine dose, with most children being diagnosed two to three days after vaccination.

The researchers also noted that the risk of developing myocarditis after getting sick with COVID-19 was much higher than after COVID-19 vaccination (11 cases per 100,000 COVID-19 infections compared to 2.7 cases per 100,000 vaccinated people).

Long-term vaccine effects

We clearly need more data on the COVID-19 vaccine’s reduction of serious disease for children. There are fortunately few negative outcomes regardless of vaccination status, although unvaccinated children are at greater risk of severe disease, hospitalization, and death.

One study found that during the Omicron-predominant period, cumulative hospitalization rates among unvaccinated children ages 5 to 11 years were 2.1 times higher than among vaccinated children. Most (87%) children ages 5 to 11 years hospitalized during the Omicron-predominant period were unvaccinated.

There is more compelling evidence for the benefit of the COVID-19 vaccine’s reduction of severe disease among adults, and for a while, we will likely have to do some extrapolations from these studies to better understand potential severity in unvaccinated or partially vaccinated children.