FDA weighs risk of myocarditis in review of Pfizer's COVID-19 vaccine for kids 5-11

The Food and Drug Administration said Friday it concluded the "overall benefits" of Pfizer's COVID-19 vaccine for children 5 to 11 years old "may still outweigh the risks," after the agency estimated that in most scenarios the vaccine could prevent more COVID-19 hospitalizations in younger children than cause a serious side effect linked to the shot.

The agency's analysis of Pfizer's vaccine was posted late Friday, ahead of a meeting of the FDA's outside vaccine experts who will be discussing next week whether the agency should grant emergency authorization to vaccinate younger children. 

Some of the FDA and CDC's outside vaccine advisers have wrestled for months with the possibility that the risk of myocarditis and pericarditis associated with the vaccine in children may exceed the COVID-19 risks diminished by the shots. 

"Before we recommend a vaccine for younger children and adolescents I think we really need to know exactly what is the risk-benefit ratio," Dr. Cody Meissner, a member of the FDA's Vaccines and Related Biological Products Advisory Committee, said at a meeting of the panel earlier this month.

Compared to adults, COVID-19 cases in children tend to be milder and are far less likely to result in hospitalization. However, a small number of children with no underlying conditions have been hospitalized, and at least 146 have died from the disease between the ages of 5 to 11 years old. Around half of hospitalized children have an underlying medical condition that could increase their risk, according to CDC data, most commonly obesity.

Myocarditis and pericarditis are types of heart inflammation that have been reported after the mRNA-based Pfizer and Moderna vaccines, typically after the second dose. Symptoms include chest pain, faster heartbeat and shortness of breath, according to the CDC, which also says on its website that "[m]ost patients with myocarditis or pericarditis who received care responded well to medicine and rest and felt better quickly."

Most cases after the vaccine have occurred in younger males and required hospitalization, federal health officials say, though the data suggests cases remain "rare" and typically subside on their own within a day.

In its review, the FDA modeled a variety of "benefit-risk outcome" situations based on different estimates of vaccine effectiveness and rates of COVID-19 in the community. 

In all of the scenarios that the FDA modeled, the agency estimated that Pfizer's COVID-19 vaccine would more frequently prevent COVID-related cases in children than cause "excess myocarditis cases." 

However, if cases of COVID-19 were to fall to the low levels last seen in June, the FDA predicted the U.S. might not see enough severe COVID-19 cases in children to outnumber the incidents of myocarditis or pericarditis.

At that level, the FDA said it was possible that the vaccine might lead to 21 prevented COVID-19 hospitalizations and 58 excess hospitalizations for myocarditis, per million children vaccinated. 

"The model results indicate that the benefits of the vaccine are highly dependent on the incidence of COVID-19," the FDA said.

Still, bearing in mind that hospitalization for COVID-19 often results in more serious long-term ill effects than myocarditis, the agency concluded that the "overall benefits of the vaccine may still outweigh the risks" in even that scenario. 

Early data from Pfizer suggests the vaccine, reduced in potency for children as young as 5, was more than 90% effective at preventing symptomatic cases of COVID-19. The FDA said it has not yet finished fully vetting the data from Pfizer's submission. 

After reducing the size of its dose, Pfizer said its trials had turned up mostly mild side effects, no new safety concerns, and no cases of myocarditis or pericarditis.

Earlier this year, the committee urged companies to expand enrollment for their pediatric trials to watch for myocarditis and pericarditis, though both Pfizer and the FDA acknowledged that even the expanded trials submitted by the company may be too small to truly assess the rates of heart inflammation. 

Pfizer also cited recent Israeli surveillance data underscoring the public health need for its shots, suggesting that rates of myocarditis could be lower in younger children and that the vaccine was effective there at curbing a wave of cases from the Delta variant.

A growing body of evidence suggests children can be just as likely to catch and spread COVID-19 as adults, even if they are less likely to face a severe case of COVID-19, and some can face long term side effects from the disease. 

"There is a concern that we may need to really get the maximum vaccination in place of as many people, including the younger children, in order to really get this pandemic under control," Dr. Peter Marks, the FDA's top vaccine official, told a webinar hosted by the group Made to Save earlier this month.