There is a way to know if children are immune to Covid (but it is virtually impossible)

Even kids can get Covid, we know. However, the aspects that generate the most questions are different: How long does the immunity that the little ones have acquired against the virus last after infection? Should they be vaccinated? As we wonder, the US Food and Drug Administration (FDA) has just given the green light for the “emergency use” of Moderna and Pfizer’s Covid vaccines for children aged 6 months to 5 years. It is a decision that underlines an article in New York Times, comes too late and could have come earlier if not “the agency and the manufacturers” had chosen to assess not only “blood levels of antibodies”, but also other components of the immune system. In that case, “it had been clear from the outset that vaccines could have prevented serious illnesses and infections in younger children,” it points out.

In particular, the researchers say, vaccine manufacturers should have measured so-called T lymphocytes. It is a type of white blood cell that specializes in recognizing cells that are infected with the virus and that is an essential part of the immune system: they act as an effective second line of defense after activating antibodies that represent only one manifestation of the immune response to Covid (according to some studies, not the best). They are also essential because, although they do not prevent infection, they are essential for reducing the severity of the disease, recognizing and eliminating the cells infected by the virus. Their measurement “would have allowed us to make a different decision and would have allowed the vaccine to be approved more quickly,” said John Wherry, director of the University of Pennsylvania Institute of Immunology, among 70 signatories of a letter sent to officials. FDA in April.

Infants actually develop an immune response to Covid-19 that is rapid but less lasting, characterized by a smaller amount of T lymphocytes. This means that young patients have a greater risk of reinfection in the long term and that they have acquired immunity naturally . is not enough: vaccination can improve their defenses. It appears from a recent study published by the prestigious journal Immunitycoordinated by the Australian Peter Doherty Institute for Infection and Immunity.

The research focused on the immune response of over 50 unvaccinated children who developed SARS-Cov2 infection, compared with the immune response of just as many unvaccinated adults. The analyzes showed that children develop a rapid immune response: This would explain why Covid tends to be less aggressive or even asymptomatic with them. However, the researchers also noted that “T cells in children had a lower frequency than in adults. We also found that not everyone who was exposed to the virus generated memory T cell responses,” Louise Rowntree explained. former signatory of the study. As mentioned, this makes children vulnerable to future infections.

For the researchers, the results of the study confirm the benefits of pediatric anti-Covid vaccination, which “specifically aims to induce the responses of memory T and B lymphocytes”. “These are the key components of our immune system that protect us from subsequent exposure to SARS-Cov2, even when new variants emerge,” says researcher Katherine Kedzierska.

In short: it is crucial to know the amount of these cells, but unfortunately measuring their mediated response requires much more sophisticated and expensive tests than those for antibodies, so quick tests and a few drops of blood are enough. “Including T cells in a vaccine study would really increase its complexity and cost. It would not be easy, but it would certainly be helpful,” said Dr. Camille Kotton, an infectious disease physician at Massachusetts General Hospital and Scientific Advisor to the Centers for Disease Control and Prevention (CDC).

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