Pfizer’s low-dose Covid-19 vaccine fails in children under 5, trial data shows

Photo: Thomas Kienzle/AFP (Getty Images)

Today has brought disheartening news to parents in the US hoping to vaccinate their young children against Covid-19 soon. Based on clinical research data, Pfizer and BioNTech announced Friday that children aged 2 to 5 did not produce a sufficient immune response to two shots of their low-dose Covid-19 vaccine, although children between 6 months and 2 years seemed to.

The companies now plan to expand their trial by adding a third low dose to the schedule, both for this age group and for children ages 5 to 12. will have to wait until the first half of next year.

The Pfizer/BioNTech study collectively included more than 4,500 children ages six months to 11 in the US, Finland, Poland and Spain. Those over the age of 5 received 10 micrograms of the vaccine (one third of the adult dose) in a two-dose schedule 21 days apart, while those under 5 years old received a 3 micrograms dose by injection.

At the end of October, the FDA authorized the Pfizer/BioNTech vaccine for children ages 5 to 11. The decision was based on data showing that the vaccine was about 90% effective in preventing coronavirus disease, and on data showing that their immune response was comparable to what had been seen in younger adults. Unfortunately, that immune response was not as robust for vaccinated children in the 2- to 4-year-old group, Pfizer/BioNTech reported Friday, based on an interim analysis of the data.

Failure will inevitably delay any vaccination program for these age groups. Although children aged six months to two years appeared to have a solid immune response, the companies made the decision (with regulatory approval) to tailor the study to all children under the age of 5. They are now receiving a third dose of 3 micrograms at least two months after the second dose. The companies also announced that they plan to study a third dose of 10 micrograms in children ages 5 to 11, as well as teens ages 12 to 17. Should the third dose appear to be effective for younger children, the companies plan to apply for an emergency use permit. (EUA) in the first half of 2022.

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The decision to use lower doses for children was based on the hope that it would provide the same protection as the adult injections, while reducing any side effects, especially the increased but rare risk of heart inflammation (myocarditis) seen in teenagers. and young adults, more in men than in women. At least there until now has not There has been evidence of major safety issues in children ages 5 to 11. The CDC has identified eight cases of myocarditis in this age group after vaccination, although it has not stated whether these cases were related to the vaccines. The cases all seemed mild and at least five have already recovered, According to the CDC.

But the latest findings indicate that it can be a difficult balance to find the optimal dose and schedule for a vaccine, for all age groups. In light of research showing that immunity is beginning to wane for those vaccinated with two doses, as well as the emergence of variants such as Delta and now Omicron, many scientists and even health officials have started to call for the mRNA vaccines to be classified as a three-dose vaccine, not a two-dose vaccine. And that seems to be the direction that Pfizer/BioNTech is heading.

In a conference call on Friday, the New York Times reported, Kathrin Jansen, Pfizer’s head of vaccine research, made it clear that the company would aim to have its vaccines approved as a three-dose series for children. And should that happen, it could pave the way for the same for all age groups.

Numerous studies have shown that people given three doses appear to have stronger protection against infection from Delta and probably Omicron, although it is still questionable how long this boost of immunity will last.

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