A better way to measure immunity in children

Some scientists believe a clearer picture of Covid vaccine effectiveness could have emerged earlier if researchers had tracked certain immune cells, not just antibodies.

< p class="css-at9mc1 evys1bk0">For Jacqueline Almeida, next week never comes soon enough.

She saw friends roll their eyes when she asked to meet them outside. She tried in vain to convince her sister to have her son vaccinated. Strangers told him on Twitter that putting his daughter in a mask amounted to abuse.

And yet vaccines for the youngest Americans have been delayed after delay . "It was very disappointing, month after month, to see everything grow," said Ms. Almeida, 33, who lives in Franklin, Tennessee.

But now, there is good news: The vaccines should be available in a few days for her 6-month-old son and her 2-year-old daughter. Food and Drug Administration scientific advisers on Wednesday recommended the Pfizer-BioNTech vaccine for children ages 6 months to 4 years and the Moderna vaccine for children ages 6 months to 5 years.

The agency itself licensed 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, around 18 million children in this age group will become eligible for the coronavirus vaccination for the first time, the latest element of the national vaccination strategy.

After a series of delays from regulators, however, only about one in five parents plan to have their young children vaccinated immediately, according to a recent survey.

In a letter to the F.D.A. In April, nearly 70 scientists offered their own assessment: the delay was avoidable. Their argument is technical, but with broad implications.

The agency and manufacturers chose to assess vaccines by tracking antibody blood levels, said the scientists. But if regulators had also considered other parts of the immune system, it might have been clear from the start that vaccines could prevent serious illnesses, and even infections, in young children.

< p class="css-at9mc1 evys1bk0"> In particular, according to scientists, vaccine manufacturers should have measured so-called T cells, which can kill infected cells and rid the body of the virus. This "would have allowed us to possibly make a different decision about allowing a vaccine to move forward sooner," said John Wherry, director of the University of Pennsylvania's Institute of Immunology and one of the signatories. of the letter.

"If we don't measure T cells, we miss a lot of what's going on," he added. "God, we've been here 18 months, we can put some energy into things like this at this point."

The F.D.A. 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 effectiveness of vaccines in preventing symptomatic infection in adults. But in the children's trials, investigators looked at blood levels of antibodies after vaccination, comparing them to levels seen in young adults.

The F.D.A. used this method, called immunobridging, to license 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 produce high levels of antibodies in children aged 2 to 4.

The companies decided to assess whether a third dose improved the performance of the vaccine. Then, over the winter, some young children in the clinical trial became infected with the Omicron variant.

Based on preliminary data from these infections, the F.D.A. said he would consider allowing two doses of the vaccine while companies continue to test the third – a move that