May 19: An advisory panel from The Centers for Disease Control and Prevention (CDC) has officially recommended a booster shot or third dose of the Pfizer-BioNTech Covid-19 for children ages 5 to 11 who are at least five months out from their primary doses.

Once CDC director Dr. Rochelle Walensky signs off on the CDC advisory panel's recommendation, boosters will be immediately available for eligible kids age 5 and older.

The news comes on the tails of the recent authorization by the Food and Drug Administration (FDA) earlier this week.

The booster shot is 10 micrograms, the same dosage as the primary series for the age group and a third of the dosage given to people ages 12 and up.

“While it has largely been the case that COVID-19 tends to be less severe in children than adults, the omicron wave has seen more kids getting sick with the disease and being hospitalized, and children may also experience longer term effects, even following initially mild disease,” said FDA Commissioner Robert M. Califf, M.D., in a press release.

“The FDA is authorizing the use of a single booster dose of the Pfizer-BioNTech COVID-19 Vaccine for children 5 through 11 years of age to provide continued protection against COVID-19. Vaccination continues to be the most effective way to prevent COVID-19 and its severe consequences, and it is safe. If your child is eligible for the Pfizer-BioNTech COVID-19 Vaccine and has not yet received their primary series, getting them vaccinated can help protect them from the potentially severe consequences that can occur, such as hospitalization and death.”   

April 14: Pfizer and BioNTech shared in a press release that data from a small clinical trial studying the effectiveness of a Covid booster shot show that a third dose increases antibody protection against the virus in the 5 to 11 age group.

The data has not yet been formally published or peer-reviewed. But early clinical trial results based on 140 children show that kids who received a 10 microgram booster six months after their second shot had a 6-fold increase in titers (the level of antibodies found in the bloodstream) against the original strain of the virus one month after the booster shot versus one month after the second shot.

Lab tests in 30 kids showed a 36-fold increase in antibodies against Omicron after the third dose as compared to after the second dose. What’s still not known is how long the antibodies will last. Experts say more information is needed.

No new safety concerns were noted, say representatives from Pfizer and BioNTech.

Currently, less than one-third of the 28 million 5 -to-11-year-old children in the United States have received two doses of a Covid vaccine, according to data from the CDC.

A previous study found that the effectiveness of the Pfizer vaccine waned considerably in the initial weeks and months after the second dose, which experts have said is a result of the Omicron strain’s ability to break through vaccine defenses. That waning protection led to many kids getting infected with the virus, even if they had been vaccinated.

However, experts still say vaccines are a powerful tool in preventing severe illness and hospitalization in this age group. Because it’s not known how long antibody protection from previous Covid infection will last, a vaccine is the best way to prevent future Covid infection. 

Related: Moderna will seek FDA authorization of its vaccine for kids ages 6 months to 6 years

Pfizer vaccine for kids 5 to 11 offers significantly less protection than expected after 1 month

March 1: According to data collected during the Omicron surge in New York state, the Pfizer vaccine for kids ages 5 to 11 was shown to be significantly less effective at preventing infection than the Pfizer shot for kids and teens ages 12 and up, which uses a larger dose. 

Researchers noted a steep decline in effectiveness in a one-month period following vaccination.

Between Dec. 13, 2021 and Jan. 30, 2022, researchers compared the rates of Covid cases and hospitalizations in 852,384 kids ages 12 to 17 to those of 365,502 kids ages 5 to 11 within two weeks of being fully vaccinated. 

Children in the 12 to 17 age group received two doses of the 30 microgram Pfizer shot, whereas kids in the 5 to 11 age group received two doses of the 10 microgram shot—one-third of the dosage. 

While the research has yet to be certified by peer review, the dosage difference may seem to matter: Protection from infection in older kids decreased from 66% to 51% during the time span. In younger kids, protection dropped from 68% to 12%. Most notably, during the week of Jan. 24 to 30, vaccine effectiveness in 12-year-olds was at 67%, whereas for 11-year-olds, it was at just 11%.

While we know that vaccine protection wanes after a certain time period (hence the need for boosters), this decline in 5- to 11-year-olds seems quite drastic.

But protection against hospitalization and severe disease stayed fairly strong in both age groups. In older kids, it dropped from 85% to 73%, and in younger kids, it dropped from 100% to 48%. (It’s worth noting that because the risk of hospitalization in kids ages 5 to 11 is very small, there’s a wider margin of error for these numbers, making them somewhat less reliable than those on the effectiveness against infection.)

However, the study authors and experts from The American Academy of Pediatrics (AAP) urge that the vaccine is still protective against severe disease, and for this reason, they still recommend its use. “They’re safe and will provide some protection,” Yvonne A. Maldonado, M.D., FAAP, chair of the AAP Committee on Infectious Diseases, says of vaccines in a statement. “But we may need to provide additional doses or different levels of dosing in future vaccine formulations and … kids may need to be more protected with masking in schools, etc.”

Related: Covid infection linked to an increased risk of diabetes in kids, CDC says.

Limited options

The Pfizer vaccine is currently the only shot authorized for the 5 to 11 age group, which means there’s no other option for parents looking to vaccinate their young children. 

If anything, these new findings point to the continued need for layered protections to prevent infection in young kids, including mask wearing. 

But these results come at a time when the Centers for Disease Control and Prevention (CDC) has started to roll back their masking recommendations, saying that masks are optional if your community's level of transmission is rated low or medium, depending on personal preference and your personal level of risk for severe illness. Many states and schools around the country have also relaxed their mask mandates.

These findings also do not bode well for the two-dose vaccine for kids ages 2 to 5, which was previously on track to be authorized in February but has since been paused due to a need for further research. 

Previous results from Pfizer’s clinical trials showed that the two-dose vaccine for that age group failed to produce a significant antibody response, and the company is currently testing the efficacy of a third dose.

Experts say the rise of the Omicron variant also may be partly to blame for the vaccine’s loss of effectiveness. “It’s disappointing, but not entirely surprising, given this is a vaccine developed in response to an earlier variant,” says Eli Rosenberg, deputy director for science at the New York State Department of Health, who led the study, to The New York Times. “It looks very distressing to see this rapid decline, but it’s again all against Omicron.”

A version of this post was originally published on Mar. 1, 2022. It has been updated.