Pfizer announced Friday that it plans to test a third dose of the Covid-19 vaccine in children under the age of five, because the low dose that such small children can handle may not provide the same protection that older children enjoy from just two injections.
The company does not expect the change to affect its plans to apply for an emergency use permit in the United States in the first half of next year.
As part of its ongoing clinical trials, the pharmaceutical giant has chosen a dosage of three micrograms per injection for children between the ages of six months and under five years of age. This is 10 times less than the 30 microgram doses given to adults, and significantly less than the 10 micrograms given to five to 11 year olds.
In children in the age group of two to five years, a dose of 10 micrograms caused more fever than in the older groups, forcing the company to choose a lower dose.
But with two injections of three micrograms, their immune response was found to be worse than in adolescents and young adults who received the vaccine.
Pfizer therefore decided to adjust its clinical trials to include a third dose, which was injected “at least two months after the second,” the company said in a press release.
The first two shots would stay three weeks apart.
A booster dose has been shown to increase protection against the virus in older populations.
“This amendment is not expected to significantly change our expectations that we would apply for emergency use and conditional approvals in the second quarter of 2022,” said Kathrin Jansen, head of vaccine research at Pfizer.
Pfizer also announced Friday that it had begun trials on 600 teens ages 12 to 17 to test a booster dose of 10 or 30 micrograms.
Currently, in the United States, in addition to adults, a booster dose is only allowed for adolescents ages 16 and 17.
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