(CN) — Studies of coronavirus vaccine efficacy on younger children hit a speedbump Friday, as Pfizer and BioNTech announced they will alter their clinical trial to include a third shot for children aged 6 months to 5 years after the two-dose regimen failed to live up to expectations.
A news release from the American pharmaceutical giant and German biotechnology firm explained that while no safety concerns were identified with the three-microgram vaccine dose for the younger age group, the planned two-dose regimen did not trigger adequate immune responses as compared to the 16 to 25-year-old and 6 to 24-month-old age groups.
Though the vaccine collaborators noted the dose in their study proved safe for children between 6 months and 5 years old, less than ideal immune response results found in a routine independent review prompted them to step back and evaluate the effects of a third dose administered at least two months after the second dose to try to ensure high levels of protection for the age group.
The decision to test a third dose “reflects the companies’ commitment to carefully select the right dose to maximize the risk-benefit profile,” Pfizer and BioNTech said. Should the three-dose study prove successful, the two companies expect to hand over data to regulators in support of emergency use authorization for 6-month to 5-year-old children in the first half of 2022.
The study germane to Friday's alterations enrolled up to 4,500 children aged 6 months to under 12 years in the U.S., Finland, Poland and Spain from more than 90 clinical trial sites.
Pfizer and BioNTech—whose Covid-19 vaccine was first approved for emergency use by the U.S. Food and Drug Administration a year ago—said they also plan to study a third 10-microgram dose of the vaccine in children aged 5 to 12 years, as well as a sub-study of a third dose of 10 or 30 micrograms in around 600 adolescents aged 12 to 17 years.
“These updates were informed by the effectiveness data for three doses of the vaccine for people 16 years and older, and the early laboratory data observed with delta and other variants of concern, including omicron, which suggest that people vaccinated with three doses of a Covid-19 vaccine may have a higher degree of protection,” the two companies explained.
These changes, they said, are endorsed by and agreed upon by the FDA and the European Medicines Agency.
Friday’s vaccine news comes amid global warnings of a renewed winter spread of the Covid-19 virus, driven largely by the tenacious omicron variant first detected in South Africa in late November and stateside in California earlier this month.
According to U.S. Centers for Disease Control and Prevention data last updated on Thursday, omicron is now present in at least 38 states. The latest integrated CDC statistics show upticks in both total reported cases and deaths from the coronavirus in the last 30 days, with U.S. totals to date hovering around 50 million cases and 800,000 deaths.
The Pfizer-BioNTech vaccine is authorized and recommended for all U.S. adults, teens and children over the age of 5, and the Moderna and Johnson & Johnson vaccines are authorized for all adults. Pfizer also announced on Tuesday that its experimental Covid pill appears effective against omicron.