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The Food and Drug Administration’s upcoming review of the Pfizer-BioNTech coronavirus vaccine for young children is unprecedented in recent history.

Next week, the agency’s scientific advisors will decide whether to approve a two-dose vaccine for children 6 months to 4 years old before clinical trials show the full course — three doses — to be effective. Many experts say such an authorization would be a first for the agency.

In fact, the intermediate results from the trial suggest that two doses of the vaccine did not produce a strong immune response In children aged 2 to 4 years, the results of the third dose trials are expected within a few weeks.

The companies applied for authorization at the insistence of the FDA, which is quite unusual. Fast-moving epidemic strains federal health officials making important decisions with limited data firstand they argue it’s important to start vaccinating young children before a new, potentially more dangerous variant arrives.

But The agency’s review of missing data as a basis for authorization has alarmed some experts.

D., founder and director of the Mayo Vaccine Research Group in Minnesota and editor-in-chief of Vaccine magazine. “We’ve never done this before, that’s what gives me some pause,” Gregory Poland said. “I don’t like the lack of more data.”

Poland and some other experts said the third dose is likely to build immunity in young children, but does not guarantee it. With the Omicron surge waning, many scientists think the agency can afford to wait for the results of the third shots, which are expected in just a few weeks.

Allowing a vaccine before then could undermine public confidence in the regulatory process and deter parents who are already worried about getting their children vaccinated, they warn. What if the third dose doesn’t work and millions of parents have already given their children the first two doses?

While children generally do not become seriously ill when infected with the coronavirus, more were hospitalized during the Omicron surge than at any other point in the pandemic. But more than one studies Children hospitalized with Covid conditions leading to Them serious illnessincluding diabetes, chronic lung disease or heart problems.

Some experts said that instead of having the vaccine approved for all 18 million children aged 6 months to 4 years, they may consider recommending it only for high-risk children until more evidence becomes available.

Still, the flood of infections during the Omicron surge has made some parents eager for the vaccine.

“On one side, parents are desperate to protect their children. On the other, there is extreme mistrust,” said Natalie Dean, a biostatistician at Emory University in Atlanta. “The whole process will need to be approached with caution and with a lot of transparency.”

The FDA’s scientific advisors will meet on February 15 to weigh the available data, which will be released Friday. The Centers for Disease Control and Prevention may recommend a two-dose regimen for the youngest children shortly thereafter.

The Biden administration has promised to respect the advisers’ advice. Surgeon general Dr. “Please know that the FDA will not cut any corners in the review process,” Vivek Murthy told reporters last week. “They know they are the gold standard we all rely on.”

As with supportive recommendations for all adults, pressure to vaccinate children is part of management’s plan for the future: Omicron may be on the way out, but children must be protected before the next, according to two federal officials familiar with the controversy. The variant has arrived.

“We are also concerned about the notable increase in reports of children experiencing long-term symptoms of COVID-19, including in some cases children who develop autoimmune diseases and Type 1 diabetes after having Covid-19,” said FDA spokesperson Stephanie Cacomo. aforementioned.

st. Jude Children’s Research Hospital, pediatric infectious disease specialist and Pfizer-BioNTech research researcher. Even if the vaccination of young children starts in April, it will be summer before three doses are received, Diego Hijano said. “Of course, we may have some sort of anxiety spreading around by the summer.”

But other researchers said preparing for the future is not reason enough to avoid a third-dose clinical trial. Dr. Poland said the risk-benefit calculation for young children at the moment is very different from that for adults at the start of the pandemic.

“While we’re making these thoughts for children, we’re not doing it in the smoke, fog, and chaos of war,” he said.

“As a vaccine expert, I need to sit down and think about it,” Poland added, regarding the FDA’s decision. “I can predict that for many of America’s parents this confusion will take much longer.”

Approving a two-dose regimen before being confident that the third dose will reduce immunity may encourage some parents to take the first two doses in hopes that it will put their children on the path to protection against the virus; others will want to wait until all data is available.

Evaluation of the Pfizer-BioNTech vaccine has progressed in stages. First came the large trials of adults that showed a result. 95 percent effectivenesslays the groundwork for rapid authorization of the vaccine for Americans aged 16 and over.

The companies then tested the vaccine in adolescents aged 12 to 15 years, but chose a dose of 10 micrograms, which is one-third the dose for adults. The companies tested three doses, 3, 10, and 30 micrograms, on the youngest children, and chose the lowest dose because it seemed both safe and powerful enough to fend off the virus.

In contrast to the adult trials, the pediatric groups were too small to measure efficacy by comparing the infection rate in those vaccinated with saline alone. Instead, the FDA set antibody levels in people ages 16 to 25 as a criterion that the vaccine must meet in these children.

This method, called immune bridging, is widely used; This was the basis for the approval of the vaccine in adolescents.

As of January 20, 1,570 children aged 6 months to 2 years and 2,328 children aged 2 to 4 years were included in the study, according to Pfizer. About twice as many children in each group received the vaccine compared to placebo.

Children ages 2 to 4 didn’t produce as many antibodies as adolescents and young adults — meaning the trial didn’t meet the bar set by the FDA, according to results Pfizer-BioNTech announced in December. The researchers decided to test a third dose in all children.

But as the research continued into December, some children were infected with the Omicron variant, giving companies insight into the vaccine’s real-world performance, according to a federal official familiar with the data who spoke about the anonymity condition.

Those figures show an efficacy of about 57 percent in children ages 2 to 4, the official said. However, there were only about 50 infections in the vaccinated and unvaccinated groups combined, so margins for error are likely wide. FDA set 30 percent as the lower limit for effectiveness in the criteria.

Dr. “If the numbers are small, the lower bound may not be above the 30 percent threshold used for adult trials,” Dean said.

More data supporting a third dose may be available soon. Infectious diseases physician at Stanford University who oversaw the experiment, Dr. “Except in any unusual circumstances, we will finish the three-dose study by March,” said Yvonne Maldonado.

He and other scientists believe the third dose will work — boosting the immune response in these kids.

“But it’s unclear what will happen in the unlikely scenario,” said Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York. “I think the approach is messy.”

If the third dose fails, companies may need to add a fourth or even fifth dose to the regimen – as with the five doses of diphtheria, tetanus and pertussis vaccine – to induce a sufficiently strong response.

The vaccine manufacturers could test two doses of 10 micrograms, which is the amount given to older children. But according to a federal official familiar with the data, in safety tests this dose caused a fever in one in five children aged 2 to 4 years.

Although this rate is comparable to the rate observed in Turkey, adolescents and young adults After the second dose, fever is much more worrisome in children younger than 5 years.

Dr. Young children with a high fever often go to emergency rooms, and visits may require antibiotics, invasive testing and hospitalization, Maldonado said. Conversely, parents may mistakenly attribute a fever to the vaccine when it could be caused by something else that requires medical attention.

Dr. “You wouldn’t want it for any age group, especially younger ones,” said Maldonado of a vaccine that produces a high fever. “If you estimate this for every child under 5 years old, that would be a lot of fever.”

The vaccine has been safe in other age groups, and even the rare risk of heart problems in adolescents is unlikely in pre-adolescent children. Still, vaccine hesitancy is running rampant among parents of young children.

The FDA authorized the Pfizer-BioNTech vaccine for children ages 5 to 11 in October. But only one-fifth of the 28 million children in this age group have been vaccinated twice. According to CDC data.

Agency under fire Approving an unproven Alzheimer’s drug called Aduhelm. Angela Rasmussen, a virologist with the Vaccines and Infectious Diseases Organization at the University of Saskatchewan in Canada, said a vaccine for the youngest children would likely be even more alarming, and any regulatory misstep could be used to discredit vaccines.

Vaccine evaluation now only advances authorization by a few weeks, he said.

“Given the potential long-term risks to vaccine confidence and uptake, isn’t it worth the time to make sure regulatory decisions are strongly supported by data?”