A booster shot of the Covid vaccine made by Pfizer-BioNTech increased the level of neutralizing antibodies against both the original version of the virus and the Omicron variant in a small trial of children age 5 to 11, the companies announced on Thursday.
If the companies’ claims of a strong immune response pass muster with federal regulators, the government could broaden eligibility for booster doses to include 28 million more children.
The study by Pfizer and BioNTech, which the companies described in a brief news release, included 140 children who received a booster dose six months after their second shot.
The children showed a sixfold increase in antibody levels against the original version of the virus one month after receiving the booster shot, compared with one month after receiving a second dose. Laboratory tests of 30 blood samples also showed 36 times the level of neutralizing antibodies against the Omicron variant compared with levels after only two doses, according to the news release and a Pfizer spokeswoman.
The companies said they would ask the Food and Drug Administration for emergency authorization of a booster dose for 5- to 11-year-olds “in the coming days.” The agency has typically acted within a month of receiving such requests.
Currently, everyone 12 and over in the United States is eligible for at least one booster dose, and about 30 million people age 50 or older are eligible for a second one. Studies suggest that 5- to 11-year-olds may be particularly in need of a booster dose.
Researchers in New York State recently found that while two shots of Pfizer’s vaccine protected children in that age group from serious illness, they provided virtually no protection against symptomatic infection, even just a month after full immunization.
The companies’ announcement comes as cases are again ticking up slightly after two months of sustained declines. The upswing has been particularly noticeable in the Northeast, where the BA.2 subvariant, now the dominant version of the virus in the United States, first took hold.
Dr. Anthony S. Fauci, President Biden’s chief medical adviser, warned in recent days that the nation could see a significant increase in infections over the next several weeks. But he has said the rates of hospitalizations are unlikely to rise in tandem because so many Americans have a degree of immunity, either from vaccines or prior infections.
Several hundred children age 5 to 11 have died of Covid since the pandemic began, according to the Centers for Disease Control and Prevention, but pediatric shots have been a hard sell for many parents. Only about 28 percent of children in that age group have received two doses and would be eligible for a booster shot. Roughly 7 percent have received just one dose, the agency’s data shows.
There was an initial rush for shots after they were first offered for that age group in November, but the increase in the vaccination rate then slowed to a crawl. In the past month, for example, it rose by a single percentage point.
The share of children age 5 to 11 with at least one dose varies starkly by region, according to a study by the Kaiser Family Foundation. Five of the top 10 states with the highest vaccination rates were in New England, while eight out of the 10 states with the lowest rates were in the South.
Even though more than 250 million Americans have been safely vaccinated since the pandemic began, pediatric experts say many parents fear unknown consequences for their children. Compared with shots to protect against measles, mumps and other diseases, which have been around for decades, the Covid vaccines are brand-new.
The study done by New York researchers, posted online in late February, found that for children age 5 to 11, the Pfizer vaccine’s effectiveness against infection fell to 12 percent from 68 percent within 28 to 34 days after the second dose.
That was a steeper decline than for older adolescents and teens who received a much stronger dose. Some experts suggested that the difference in dosage explained the gap in protection, while others blamed the Omicron variant that was prevalent during the study.
Another study by the C.D.C. stated that two doses of Pfizer’s vaccine reduced the risk of Omicron infection by 31 percent among those age 5 to 11, compared with a 59 percent reduction in risk among those age 12 to 15.
Pfizer’s vaccine is so far the only one authorized for those under the age of 18.