The Pfizer and Moderna COVID-19 vaccines in children aged 5 though 11 years.

Both mRNA vaccines approved in the US for adults have now provided data on their performance in children aged 5 through 11. The target is the more than 28 million children in this age group in the U.S. We currently have much more data on children with the Pfizer vaccine, as the Moderna results were announced only yesterday. Importantly, there are similarities between the two vaccines proposed for these children, but there are also some significant differences.

The biggest difference between the proposed children’s vaccines for this age group is the actual amount of RNA given. The Pfizer vaccine for this age group is 1/3 the adult dose, or 10 milligrams total. In contrast, the Moderna vaccine is 1/2 the adult dose, or 50 milligrams total. The Pfizer vaccine is given in two doses, three weeks apart while the Moderna vaccine’s two doses are given four weeks apart. These dosing regiments mirror those used in adults and adolescents.

Both companies indicate strong immune responses to the SAR-CoV-2 spike protein in almost all children. In many cases these antibody responses are higher than those seen in older individuals. In addition, the FDA has now confirmed Pfizer’s data showing the vaccine was 90.7% effective at preventing symptomatic Covid-19. The FDA stated it found “the vaccine was to be safe and tolerable” in a document the agency posted online last Friday morning. 

Pfizer said a review of data for 2,268 children in the trial showed that those who received two 10-microgram doses had antibody levels one month after the second dose like those found in people aged 16 to 25 years who received the 30-microgram doses in a separate Pfizer study. However, the children’s study was smaller than the hundreds of thousands of adults that were previously tested, and the 90.7% efficacy rate was based on the finding that three children who received the vaccine became sick with Covid-19, as compared with 16 cases in children who received a placebo.

There appeared to be fewer side effects such as fever and chills among younger children who got the vaccine compared with 16-to-25-year-olds, according to Pfizer. There also were no cases of myocarditis, an inflammatory heart condition that is a rare side effect in young men particularly with the Moderna vaccine. Again, however, these rare side effects might not be detected in a smaller study.

Today, the FDA has convened a panel of outside experts to review the data and advise on authorization. Vaccination among children age 5 to 12 could start within weeks, if the FDA issues the authorization requested by Pfizer and BioNTech.  That means children could be immunized before the holidays.

Given the smaller sized studies, the differences in dosing and the lower risk for severe COVID-19, many will question the need to vaccinate these children. Let me try to lay out the risk/benefit analysis.

The risks are better defined. Especially with Pfizer, the vaccine appears to be well tolerated. Rare side effects could occur but given the experience in hundreds of millions of adults, it’s unlikely new side effects will arise. While the Pfizer effectiveness may wear off, much like it has in adults and require a booster, its initial efficacy to safety profile is excellent.

The lower dose of the Pfizer vaccine also reinforces safety. In adults, as compared with Pfizer vaccine, the 3-fold higher dose of the Moderna vaccine was associated with more side effects and higher incidence of myocarditis in young males. This difference was significant enough that Norway has advised that all people under 18 years shouldn’t be given the Moderna vaccine, and recommended that men under 30 consider getting the Pfizer-BioNTech vaccine instead. Pfizer’s pediatric dose in now 1/5 the proposed Moderna dose (10 mg vs. 50 mg), so the safety difference might be even greater. So, I would default to using the Pfizer vaccine in this age group.

The benefits of immunizing these children are less well-defined but outweigh the risks. This age group can get sick from Covid-19, though these children tend to experience mild cases and unless immune compromised are much less likely than adults to be hospitalized or die from the virus. Some reports have indicated more children were infected and sick this summer, which was tied to the highly contagious Delta variant by the CDC. Given this, there is direct and significant protection provided to these children from this vaccine.

In contrast, the most compelling reason for vaccinating these 28 million children is an indirect benefit. Most public health authorities believe these children need to be vaccinated to achieve “herd immunity” that reduces further spread of the virus to others. While some have argued children do not spread COVID-19, they were more likely to spread the Delta variant.

This last argument is powerful and correct but would carry more weight if all adults already had agreed to be immunized!