Pfizer says 3 COVID-19 shots protect children under 5

Three doses of Pfizer-BioNTech's COVID-19 vaccine offer strong protection for children younger than five, the companies announced Monday. Pfizer plans to give the data to U.S. regulators later this week in a step toward letting the littlest kids get the shots.

The news comes after months of anxious waiting by parents desperate to vaccinate their babies, toddlers and preschoolers, especially as the number of U.S. COVID-19 cases once again is rising. The 18 million children under five are the only group in the U.S. not yet eligible for COVID-19 vaccination.

Health Canada has not yet approved mRNA COVID-19 vaccines for children under five. 

Pfizer told CBC News Monday morning that they are in discussions with Health Canada regarding a vaccine for children under five, but cannot comment on timelines.

The U.S. Food and Drug Administration has begun evaluating data from Pfizer's rival Moderna, which hopes to begin offering two kid-sized shots by summer.

Pfizer has had a bumpier time figuring out its approach. It aims to give children under five just one-10th of the amount adults receive — an even lower dose than the one for kids age five to 12. However, the company discovered during its trial that two shots at that dose didn't seem quite strong enough for preschoolers. So researchers gave a third shot to more than 1,600 youngsters — from age six months to four years — during the winter surge of the Omicron variant.

In a media release, Pfizer and its partner BioNTech said the extra shot did the trick, revving up the children's levels of virus-fighting antibodies enough to meet FDA criteria for emergency use of the vaccine with no safety problems.

Preliminary data suggested the three-dose series is 80 per cent effective in preventing symptomatic COVID-19, the companies said, but they cautioned the calculation is based on just 10 cases diagnosed among study participants by the end of April. The study rules state that at least 21 cases are needed to formally determine effectiveness, and Pfizer promised an update as soon as more data is available.

The companies already had submitted data on the first two doses to the FDA, and BioNTech's CEO, Dr. Ugur Sahin, said the final third-shot data would be submitted this week.

"The study suggests that a low, 3-microgram dose of our vaccine, carefully selected based on tolerability data, provides young children with a high level of protection against the recent COVID-19 strains," he said in a statement.

Regulatory approvals still required

What's next? FDA vaccine chief Dr. Peter Marks has pledged the agency will "move quickly without sacrificing our standards" in evaluating dose sizes for children under five from both Pfizer and Moderna.

The agency has set tentative dates next month for its scientific advisers to publicly debate data from each company.

Moderna is seeking to be the first to vaccinate the littlest kids. It submitted data to the FDA saying small children develop high levels of virus-fighting antibodies after two shots that contain a quarter of the dose given to adults. The Moderna study found effectiveness against symptomatic COVID-19 was 40 to 50 per cent during the Omicron surge, much like for adults who've only had two vaccine doses.

Complicating Moderna's progress, the FDA so far has allowed its vaccine to be used only in adults.

Last month, the company told CBC News that it hopes to complete the application for regulatory approval of its COVID-19 vaccine in children ages five and under shortly.

The FDA is expected to review Moderna's data on both the youngest age group and its study of teens and elementary-age children. Health Canada authorized Moderna's shots for kids between the ages of six and 11 in March. Last fall, it expanded the Pfizer shot to kids between the ages of five and 11.

While COVID-19 generally isn't as dangerous to youngsters as to adults, some children do become severely ill or even die. And the Omicron variant hit children especially hard, with those under five hospitalized at higher rates than at the peak of the previous Delta surge.

It's not clear how much demand there will be to vaccinate the youngest kids. Pfizer shots for five- to 11-year-olds opened in November, but only about 30 per cent of that age group have gotten the recommended initial two doses. In Canada, 41 per cent of the five- to 11-year-old population is considered fully vaccinated.

Last week, U.S. health authorities said elementary-age children should get a booster shot just like everyone 12 and older is supposed to get, for the best protection against the latest coronavirus variants.