For Jacqueline Almeida, next week may not come soon.
He looked his friends in the eye when he asked them to meet outside. She has tried unsuccessfully to persuade her sister to vaccinate her son. She was told on Twitter by strangers that wearing a mask on her daughter was tantamount to child abuse.
And yet vaccines for younger Americans faced delays after delays. “It was very frustrating, month after month, to see everything being pushed,” said Mrs. Almeida, 33, who pulls Franklin.
But now there is some good news: her 6-month-old son and 2-year-old daughter should get the vaccine in a few days. On Wednesday, the Food and Drug Administration’s scientific advisers recommended the Pfizer-BioNTech vaccine for children 6 months to 4 years old and the Moderna vaccine for children 6 months to 5 years old.
The agency itself approved the vaccines on Friday, and the Centers for Disease Control and Prevention will likely follow suit on Saturday. If all goes according to plan, about 18 million children of this age will be eligible to be vaccinated against the coronavirus for the first time, which is the final part of the country’s vaccine strategy.
After a series of delays by regulators, however, according to a recent survey, one in five parents plan to vaccinate their young children now.
In a letter to FDA officials in April, about 70 scientists proposed their own assessment: the delay was preventable. Their argument is a technical one, but with far-reaching implications.
The agency and the manufacturers chose to evaluate the vaccine by tracking the blood levels of the antibodies, the scientists said. But if regulators had considered other parts of the immune system as well, it might have been clear early on that vaccines could prevent serious illness if not transmitted to young children.
In particular, the scientists argued, vaccine makers should have measured the so-called T cells, which could kill infected cells and rid the body of the virus. John Harry, director of the Institute for Immunology at the University of Pennsylvania and one of the signatories to the letter, said “before we were allowed to make a different decision about allowing a vaccine to go ahead.”
“If we don’t measure T cells, we’re missing a big part of what’s happening,” he added. “My God, we’ve been in it for 18 months, we can dedicate some energy to things like this right now.”
The FDA declined to comment on the letter, but Dr. Harry said agency officials called scientists about a month ago to discuss their ideas.
Vaccine manufacturers conduct large-scale experiments to measure the effectiveness of vaccines in preventing significant infections in adults. But in pediatric tests, investigators looked at blood levels of the antibody after vaccination, comparing it to levels seen in young people.
The FDA used this method, called immunobridging, to approve the Pfizer-BioNTech vaccine for children 5 to 11 years of age and adolescents 12 to 15 years of age. But in December the companies reported that two doses of their vaccine did not produce high antibody levels. Children aged 2 to 4 years.
The companies have decided to evaluate whether the third dose has improved the effectiveness of the vaccine. Then, in the winter, some young children in clinical trials were infected by the Omicron variant.
Based on preliminary data on this infection, the FDA says it will consider approving two doses of the vaccine while companies continue to test a third – a decision that has provoked mixed reactions from parents and experts.
But the number of infections among children has risen, and the data collected did not support the FDA’s decision, prompting the agency to cancel its planned review. As Omicron variants spread across the country, parents are confused and put their children at risk.
The CDC reported in April that about 75 percent of children could be infected with the coronavirus by March, many of them during omikron growth. A record number of children were hospitalized, although still in much lower numbers than adults.
Experts said in an interview that more information about T-cell immunity produced by the vaccine could provide shots soon to frustrated parents and prevent at least some hospitalization.
Antibodies are essential to neutralize the virus upon entry and to prevent infection, and these can easily be measured in just one or two bloods. But when doing dozens of quick tests for antibody levels, it is necessary to test at least a few milliliters of blood and at least a few samples a day for T cell evaluation.
Incorporating T cells into the vaccine analysis would “really increase the complexity and cost of the study,” said Dr. Camille Cotton, an infectious disease physician at Massachusetts General Hospital and scientific adviser to the CDC.
“It’s never as simple as antibodies, but it will definitely be helpful,” he said.
And not everyone is sure that T cells are an important metric for immunity. Dr Miles Davenport, an immunologist at the University of New South Wales in Sydney, said low levels of antibodies could be enough on their own to prevent serious disease.
“There are no studies that show that vaccine-induced T cell levels predict the risk of infection or serious disease,” said Dr. Davenport.
Still, epidemiological data indicate that even though antibody levels decreased and infections increased rapidly, vaccinated individuals had relatively fewer hospitalizations and deaths. It suggests that antibody levels protect people from serious illnesses other than those, Dr. Werry said.
“Mortality is only increasing in very old populations or those who are immunocompromised, where we had a deficiency or had a weak T cell response,” he added. “There’s a lot of good situational information out there, but we’re really missing a smoking gun.”
A new initiative from the University of Pennsylvania may offer some answers. Known as the Immune Health Project, the study will simultaneously evaluate antibody and T cell responses in immunocompromised patients after vaccination.
Unanswered questions about children’s immunity may explain why about 40 percent of parents of young children go on vaccinations: less than 30 percent of children between the ages of 5 and 11 have received two doses, and the demand for the youngest children may be even lower.
Monica Lowe, 35, an assistant principal at a school in Seattle, is among those in doubt. “The covid vaccine is happening so fast and so fast that we wanted to give it some more time,” he said.
Mrs. Lowe and her husband have both been fully vaccinated, but their 7-year-old son, Xian, received only one vaccine in January before a planned trip to Hawaii. Ms Lowe said they decided to delay her second dose because of information suggesting that doing so could create better immunity.
The couple also has a 2-year-old daughter and Mrs. Lowe is pregnant with their third child, in July. But they still have no plans to vaccinate their daughter, Ms Lowe said: “We will not be in the front row.”