For Jacqueline Almeida, next week can’t come soon enough.
She has watched friends roll their eyes when she asks to meet them outdoors. She has tried unsuccessfully to convince her sister to vaccinate her son. She was told by strangers on Twitter that putting her daughter in a mask was tantamount to child abuse.
And yet the vaccines for the youngest Americans faced delay after delay. “It was very disappointing, month after month, seeing everything get pushed,” said Ms. Almeida, 33, who lives in Franklin, Tenn.
But now there’s some good news: Vaccines should be available for her 6-month-old son and 2-year-old daughter. Scientific advisers recommended on the Food and Drug Administration Wednesday the Pfizer-BioNTech vaccine for children aged 6 months through 4 and the Moderna vaccine for children aged 6 months through 5.
The agency itself authorized the vaccines on Friday, and the Centers for Disease Control and Prevention is expected to follow suit on Saturday. If all goes according to plan, about 18 million children in this age group will become eligible for immunization against the coronavirus for the first time, the final piece in the nation’s vaccine strategy.
After a series of delays by regulators, however, only about one in five parents plan to have their young children immunized right away, according to a recent survey.
In a letter to FDA officials in April, nearly 70 scientists offered their own assessment: The delay was preventable. Their argument is a technical one, but with broad implications.
The agency and the manufacturers have chosen to evaluate the vaccines by tracking blood levels of antibodies, the scientists said. But had regulators also considered other parts of the immune system, it may have been clear early on that vaccines could prevent serious illness, if not infection, in young children.
In particular, the scientists argued, vaccine manufacturers should be measuring so-called T cells, which can kill infected cells and rid the body of the virus. That “would have allowed us to possibly make a different decision about moving a vaccine to the forefront,” said John Wherry, director of the Institute for Immunology at the University of Pennsylvania and one of the letter’s signatories.
“If we don’t measure the T cells, we’re missing a big part of what’s happening,” he added. “My gosh, we’re 18 months into this, we can devote a little bit of energy to stuff like that at this point.”
The FDA declined to comment on the letter, but Dr. Wherry said agency officials called the scientists about a month ago to discuss their ideas.
Vaccine manufacturers have conducted large trials to measure the efficacy of the vaccines in preventing symptomatic infections in adults. But in the children’s trials, investigators looked at blood levels of antibodies following vaccination, comparing them with the levels seen in young adults.
The FDA used this method, called immunobridging, to authorize the Pfizer-BioNTech vaccine for children aged 5 to 11 and for adolescents aged 12 to 15. But in December, the companies reported that two doses of their vaccine did not produce high antibody levels. children aged 2 to 4.
The companies decided to assess whether a third dose improved the vaccine’s performance. Then, over the winter, some young children became infected with the Omicron variant.
Based on preliminary data from those infections, the FDA said it would consider authorizing two doses of the vaccine while companies continued to test the third – a decision that provoked mixed reactions from parents and experts.
But the number of infections in children grew, and accruing data did not support the FDA’s decision, prompting the agency to cancel its planned review. The back-and-forth left parents confused and their children vulnerable, as the Omicron variants ramped through the nation.
The CDC reported in April that about 75 percent of children were infected with the coronavirus by March, many of them during the Omicron surgeon. Record numbers of children were hospitalized, though still much lower than adults.
More information about T-cell immunity generated by vaccines may have been delivered to desperate parents sooner and prevented at least some of those hospitalizations, experts said in interviews.
Antibodies are essential for neutralizing the virus on entry and preventing infection, and they can be easily measured in just a drop or two of blood. But while there are dozens of rapid tests for antibody levels, assessing T cells requires at least a few milliliters of blood and at least a few samples a day to test.
A vaccine analysis in Including T cells would “really up the complexity and cost of the study,” said Dr. Camille Kotton, an infectious disease physician at Massachusetts General Hospital and a scientific adviser to the CDC
“It’s never as easy as antibodies, but it would definitely be helpful,” she said.
And not everyone is convinced that T cells are an important metric for immunity. Low levels of antibodies may be sufficient to prevent severe disease on their own, said Dr. Miles Davenport, an immunologist at the University of New South Wales in Sydney.
“There is no study demonstrating that the level of vaccine-induced T cells is predictive of either a risk of infection or a risk of severe disease,” Dr. Davenport said.
Still, epidemiological data suggest that even as antibody levels dropped and infections rose sharply, hospitalizations and deaths in vaccinated people remained relatively low. That suggests that antibody levels are protected from people with severe illness, Dr. Wherry said.
“Mortality is only growing in the very old population or those who are immunocompromised, where we lacked or had poor T cell responses,” he added. “There’s a lot of good circumstantial data out there, but we’re really missing a smoking gun.”
A new initiative at the University of Pennsylvania may deliver some answers. Called the Immune Health Project, this study will simultaneously assess antibody and T cell responses in immunocompromised patients after vaccination.
Unanswered questions about immunity in children may explain why roughly 40 percent of parents’ young children are on immunization: Fewer than 30 percent of children aged 5 to 11 have received two doses, and the demand for the youngest children may be even lower General Chat Chat Lounge
Monica Lo, 35, who is an assistant principal at a school in Seattle, is among the hesitants. “Covid vaccination is happening so fast and so fast that we wanted to give it a little bit more time,” she said.
Ms. Lo and her husband are both fully vaccinated, but their 7-year-old son, Gian, had only one shot at vaccinating before a planned trip to Hawaii in January. They decided to delay their second dose because of data suggesting that doing so might produce better immunity, Ms. Lo said.
The couple also has a 2-year-old daughter, and Ms. Lo is pregnant with their third child, due in July. But they don’t plan to vaccinate their daughter just yet, Ms. Lo said: “We will not be first in line.”