For Jacqueline Almeida, next week can’t come soon enough.
She saw her friends roll their eyes when she asked to meet them outdoors. She unsuccessfully tried to convince her sister to vaccinate her son. Strangers told her on Twitter that putting a mask on her daughter was tantamount to child abuse.
Yet vaccines for the youngest Americans have faced delay after delay. “Month after month, it has been very frustrating to see things moving forward,” said Ms. Almeida, 33, who lives in Franklin, Tennessee.
But now there is good news: in a few days, vaccines should be available for her 6-month-old son and 2-year-old daughter. FDA scientific advisors on Wednesday recommended the Pfizer-BioNTech vaccine for children 6 months to 4 years of age and the Moderna vaccine for children 6 months to 5 years of age.
The agency itself authorized vaccines on Friday, and the Centers for Disease Control and Prevention is likely to follow suit on Saturday. If all goes according to plan, some 18 million children in this age group will be eligible for coronavirus immunization for the first time, the final element of a national vaccination strategy.
However, after a series of regulatory delays, only one in five parents plan to have their young children vaccinated right away. one recent poll.
In a letter to FDA officials in April, about 70 scientists offered their own assessment: the delay could have been prevented. Their argument is technical, but with broad implications.
The agency and manufacturers decided to evaluate vaccines by monitoring blood levels of antibodies, scientists said. But if regulators also considered other parts of the immune system, it could be clear that vaccines can prevent serious illness, if not infection, in young children.
In particular, scientists argued, vaccine manufacturers had to measure the so-called T-cells, which can kill infected cells and rid the body of the virus. This “would allow us to possibly make a different decision about releasing the vaccine sooner,” said John Warry, director of the University of Pennsylvania’s Institute of Immunology and one of the letter’s signatories.
“If we don’t measure T cells, we’re missing out on a lot of what’s going on,” he added. “Oh my God, we’ve been doing this for 18 months, we can devote some energy to things like this at the moment.”
The FDA declined to comment on the letter, but Dr. Werry said the agency called the scientists about a month ago to discuss their ideas.
Vaccine manufacturers have conducted extensive trials to measure the effectiveness of vaccines in preventing symptomatic infection in adults. But in trials in children, the researchers looked at levels of antibodies in the blood after vaccination, comparing them to levels seen in young adults.
The Food and Drug Administration (FDA) used this method, called immune bridging, to approve the Pfizer-BioNTech vaccine for children ages 5 to 11 and adolescents ages 12 to 15. But in December, the companies reported that two doses of their vaccine did not cause high levels of antibodies in children aged 2 to 4 years.
The companies decided to evaluate whether the third dose improved the effectiveness of the vaccine. Then, during the winter, several young children participating in clinical trials became infected with the Omicron variant.
Based on preliminary data on these infections, the FDA said it would consider authorizing two doses of the vaccine while companies continue to test a third – a decision that has drawn mixed reactions from parents and experts.
But the number of infections among children was on the rise and the incoming data did not support the FDA’s decision, prompting the agency to cancel a planned review. Back and forth, parents are confused and their children are vulnerable as Omicron variations rage across the country.
The CDC reported in April that about 75 percent of children may have been infected with the coronavirus by March, many of them during the Omicron surge. A record number of children were hospitalized, although far fewer than adults.
More information about vaccine-generated T-cell immunity could have vaccinated desperate parents earlier and prevented at least some of those hospitalizations, experts said in an interview.
Antibodies are needed to neutralize the virus upon entry and prevent infection, and can be easily measured in as little as one or two drops of blood. But while there is dozens of express tests it takes at least a few milliliters of blood to determine antibody levels for T cell evaluation and at least a day to test just a few samples.
Including T cells in vaccine analysis “is going to really complicate and cost research,” said Dr. Camille Cotton, an infectious disease physician at Massachusetts General Hospital and a scientific advisor 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 indicator of immunity. According to Dr. Miles Davenport, an immunologist at the University of New South Wales in Sydney, low antibody levels may be enough to prevent serious illness.
“There are no studies demonstrating that vaccine-induced T-cell levels predict either the risk of infection or the risk of severe disease,” said Dr. Davenport.
Nevertheless, epidemiological data show that even with the decrease in antibody levels and the sharp increase in hospitalizations and mortality among vaccinated people, they remained relatively low. This suggests that something other than antibody levels protected people from severe illness, Dr. Werry said.
“Mortality only increases among the very elderly or immunocompromised people, where we had no or poor T-cell response,” he added. “There’s a lot of good circumstantial evidence, but we’re really missing a smoking gun.”
A new University of Pennsylvania initiative may provide some answers. called immune healththe study will simultaneously assess antibody and T cell responses in immunocompromised patients after vaccination.
Unanswered questions about immunity in children may explain why approximately 40 percent of parents of young children are hesitant about immunization: less than 30 percent of children aged 5 to 11 have received two doses, and demand for the smallest children may be even lower. .
Monica Lo, 35, a school assistant principal in Seattle, is also hesitant. “The Covid vaccination is happening so quickly and so quickly that we wanted to give it a little more time,” she said.
Ms. Lo and her husband are fully vaccinated, but their 7-year-old son, Gian, received only one shot in January before a planned trip to Hawaii. According to Ms. Lo, they decided to delay his second dose due to evidence suggesting it could boost immunity.
The couple also have a 2-year-old daughter, and Ms. Luo is pregnant with their third child due in July. But they don’t plan to vaccinate their daughter yet, Ms. Luo said, “We won’t be first in line.”