Researchers looked at immune responses, comparing them with levels in adults who had received the vaccine. Pfizer then deduced that the protection afforded by the lower dose in children could be as substantial as that afforded by the higher dose in adults. That approach is particularly important in small trials.
After the second shot, the children had levels of neutralizing antibodies that were at least equal to those of 16-to-25-year-old volunteers in another Pfizer-BioNTech trial. Although antibody levels are just one measure of the immune system’s response, experts have said such a finding would indicate that one-third of an adult dose was the proper dosage for young children.
Regulators and experts have linked the conditions of myocarditis, or inflammation of the heart muscle, and pericarditis, or inflammation of the lining of the heart, to both the Pfizer-BioNTech and Moderna vaccines, which are based on similar technology. For men under 20 who receive two full doses of one of those vaccines, the rate of myocarditis may exceed 100 cases per million doses, according to data presented at a C.D.C. meeting on Thursday.
Studies have shown that the risk of developing those heart problems from Covid-19 is higher than from vaccination. Still, some countries have recommended a single dose of the Pfizer-BioNTech vaccine for children 12 and older, offering less protection but possibly with a lower risk of side effects.
Experts will almost certainly raise concerns about those side effects at the F.D.A. advisory committee meeting, according to Dr. H. Cody Meissner, a member of the panel and the chief of the Division of Pediatric Infectious Diseases at Tufts Children’s Hospital in Boston.
What to Know About Covid-19 Booster Shots
The F.D.A. has authorized booster shots for millions of recipients of the Pfizer-BioNTech, Moderna and Johnson & Johnson vaccines. Pfizer and Moderna recipients who are eligible for a booster include people 65 and older, and younger adults at high risk of severe Covid-19 because of medical conditions or where they work. Eligible Pfizer and Moderna recipients can get a booster at least six months after their second dose. All Johnson & Johnson recipients will be eligible for a second shot at least two months after the first.
Yes. The F.D.A. has updated its authorizations to allow medical providers to boost people with a different vaccine than the one they initially received, a strategy known as “mix and match.” Whether you received Moderna, Johnson & Johnson or Pfizer-BioNTech, you may receive a booster of any other vaccine. Regulators have not recommended any one vaccine over another as a booster. They have also remained silent on whether it is preferable to stick with the same vaccine when possible.
The C.D.C. has said the conditions that qualify a person for a booster shot include: hypertension and heart disease; diabetes or obesity; cancer or blood disorders; weakened immune system; chronic lung, kidney or liver disease; dementia and certain disabilities. Pregnant women and current and former smokers are also eligible.
The F.D.A. authorized boosters for workers whose jobs put them at high risk of exposure to potentially infectious people. The C.D.C. says that group includes: emergency medical workers; education workers; food and agriculture workers; manufacturing workers; corrections workers; U.S. Postal Service workers; public transit workers; grocery store workers.
Yes. The C.D.C. says the Covid vaccine may be administered without regard to the timing of other vaccines, and many pharmacy sites are allowing people to schedule a flu shot at the same time as a booster dose.
“I certainly hope that we’re in a position to to recommend this because people are certainly waiting for it, they’re anxious to have it,” he said. “But our responsibility is to balance both risk and benefit.”
Vaccine experts have said that Pfizer’s lower dosing could mitigate risks.
Dr. Brian Feingold, an expert on heart inflammation in children at the UPMC Children’s Hospital of Pittsburgh, said that even though Pfizer’s trial was small, the overall results were still worth taking seriously.