Canada's drug regulator approved Moderna's COVID-19 vaccine for infants and preschoolers Thursday, making it the first vaccine approved for that age group in the country.

Health Canada now says the Moderna vaccine can be given to young children between the ages of six months and five years old in doses one-quarter the size of that approved for adults.

"After a thorough and independent scientific review of the evidence, the department has determined that the vaccine is safe and effective at preventing COVID-19 in children between 6 months and 5 years of age," the department said in a statement.

The National Advisory Committee on Immunization gave provinces its assent to offer the vaccine to children in that age group Thursday, by recommending that children "may" be offered the vaccine.

The committee's executive secretary, Dr. Matthew Tunis, said NACI is acknowledging that this could be an "important protective measure" for parents who want to exercise the option for their kids, and the recommendation could be strengthened as more data becomes available.

While serious illness among children is rare, the committee said the number of children hospitalized for COVID-19 shot up dramatically as the Omicron variant spread rampantly last winter.

"This authorization comes at a critical time in the pandemic as we progress through the seventh wave and though children are less likely to experience complications from COVID-19, they can still get very sick," said Dr. Supriya Sharma, Health Canada's chief medical adviser, at a media briefing Thursday.

The average monthly rate of young children hospitalized because of COVID-19 increased from 1.4 per 100,000 children under five in the first two years of the pandemic to 15.9 per 100,000 in the first three months of 2022.

Sharma pointed out that even children with mild illness can go on to develop long-term symptoms and, in rare but serious cases, multisystem inflammatory syndrome, which often requires acute hospital care.

Deputy chief public health officer Dr. Howard Njoo advocated for parents to vaccinate their kids as protection against serious illness, even if they've already been sick with COVID-19.

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Health Canada said it will continue to keep a close eye on the safety of the vaccine, and has required Moderna to provide updated data on both the safety and effectiveness of the vaccine.

In its decision posted on the Health Canada website, the agency said Phase 3 trial results for the drug show the immune response in children six months to five years old was comparable to Moderna's vaccine for 18 to 25-year-olds.

The approval expands COVID-19 vaccine eligibility to nearly two million children in Canada, though where and when the vaccine will be given to kids will be determined by provinces.

Njoo said there is a "sufficient supply" of vaccines, which will be shipped to the provinces so they can begin to offer them to children "very shortly."

So far Canadian parents have been more hesitant to vaccinate their kids against COVID-19 than they were to vaccinate themselves. As of June 19, about 42 per cent of kids between the ages of five and 11 have had two doses of an approved vaccine.

By comparison, about 90 per cent of Canadians 12 and over have had at least two shots.

Njoo said public health doesn't want to force the vaccine on families and wants them to feel comfortable with their choice. He encouraged parents to speak with their family doctors or pediatricians if they have any questions about whether their child should get the shot.

In Moderna's trials, two doses of the child-sized vaccine were given about four weeks apart, but NACI recommends waiting eight weeks between shots.

NACI also recommends a third dose for immunocompromised children, if their parents choose to vaccinate them, with a four to eight-week wait between injections.

For now, the committee says the COVID-19 vaccine should not be given to babies, toddlers or preschoolers at the same time as vaccines for other illnesses to help identify any potential reactions.

Health Canada said there were no safety concerns identified in the study. The most common reactions were similar to the ones kids experience for other pediatric vaccines, like pain at the site, sleepiness and loss of appetite.

Less commonly, some kids got a mild to moderate fever, swelling at the injection site, nausea, tender lymph nodes under the arm, headaches and muscle aches.

Health Canada said there are still some uncertainties about the vaccine because it's new and there's no long-term data available yet. For example, there's little data about the risk of very rare reactions like myocarditis, a swelling of heart tissue, though no cases came up in the trials.

There is also more to learn about the safety and effectiveness of the vaccine in young children with other health conditions or who are immunocompromised, the documents said.

The United States approved Moderna and Pfizer's pediatric COVID-19 vaccines last month, and so far have immunized 267,000 children in that age group as of July 8.

Pfizer's pediatric COVID-19 vaccine for young children between six months and five years old was submitted to Health Canada last month and is still under review.

This report by The Canadian Press was first published July 14, 2022.

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