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Rashaun Robinson, 11, receives his first vaccine as Canada's Prime Minister Justin Trudeau visits a COVID-19 vaccination clinic for children at Scarborough Health Network's Centenary Hospital in Toronto on Dec. 10, 2021.NICK LACHANCE/Reuters

Parents of young children may want to consider shortening the recommended eight-week interval between the two doses of pediatric COVID-19 vaccine in light of the arrival of the Omicron variant, medical experts say.

The National Advisory Committee on Immunization (NACI) recommends children 5 to 11 receive their second dose at least eight weeks after the first. This is based on research showing that a longer interval results in more robust immune responses and higher vaccine effectiveness.

However, this research was based on data from the adult population, and NACI’s guidance was developed before the arrival of the Omicron variant, for which there is mounting evidence that it is more transmissible than Delta and potentially better able to spread among the vaccinated population.

NACI’s recommendation of eight weeks is also, in part, because emerging Canadian safety surveillance data suggest an extended interval may reduce the risk of myocarditis, an inflammation of the heart muscle, that has been reported very rarely following vaccination, most commonly in people 12 to 30. These data were from adolescents and young adults who received the adult dose of the vaccine, which is three times that of the pediatric version.

In the U.S., where children are receiving their second doses three weeks after the first, the Centers for Disease Control and Prevention reported this week that, with more than 7.1 million doses of the pediatric vaccine administered, there were eight reported cases of myocarditis. Of six reports with known outcomes, five children had since resolved their symptoms and one was still recovering.

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Tehseen Ladha, an Edmonton-based pediatrician and assistant professor of pediatrics at the University of Alberta, advised families to consider the information and their own personal circumstances and discuss the matter with their family doctors.

“I think it’s very worthwhile to consider shortening the interval between the two doses, given that Omicron is here and it’s in schools and it’s going to spread quite quickly,” she said.

“Part of the saving grace is if people follow rules and keep to small bubbles over the holidays, we won’t necessarily have to worry about widespread infection with Omicron until the new year, when kids are back in school, among the pediatric population. But I think each family needs to personally weigh the information. The reason it was eight weeks was these theoretical risks and benefits.”

Alexander Wong, an infectious-diseases physician based in Regina, said what is known about Omicron makes a compelling case for shortening the interval between doses.

He advised parents to consider their family’s overall risk profile, such as whether there is someone who is medically vulnerable in their bubble and what case counts are like in their region. He added that daycares and schools are higher-risk settings, and there is merit in optimizing protection before classes resume after the winter break.

“Given what we know about Omicron, given the fact that we know that having more doses of vaccine is going to provide better protection against getting infected, and better protection against severe illness, hospitalizations and deaths, that makes sense to me as a physician and as a parent of a five-year-old,” Dr. Wong said. He is aiming for a three- to four-week interval for his son.

A spokesperson for Pfizer, which developed the Comirnaty vaccine with BioNTech, said Health Canada authorized the pediatric vaccine based on data from a randomized, controlled trial that included about 4,600 children at the age of 5 to 11, following a two-dose schedule three weeks apart.

“We recognize that recommendations on alternative dosing intervals reside with health authorities and may include adapting public-health recommendations in reaction to evolving circumstances during a pandemic. However, as a biopharmaceutical company working in a highly regulated industry, our position is supported by the label and indication agreed upon with Health Canada,” Christina Antoniou wrote in an e-mail.

“The safety and efficacy of the vaccine has not been evaluated on different dosing schedules as the majority of trial participants received the second dose within the window specified in the study design.”

Most provinces strongly recommend the eight-week interval but allow for parental discretion. Saskatchewan, for example, allows second doses as early as three weeks after the first. Ontario permits an interval shorter than eight weeks with informed consent and recommends parents speak with their primary-care providers. Alberta says parents can call HealthLink 811 to book a shorter interval if their child is immunocompromised, or if the second shot is needed sooner for travel purposes.

In B.C., Health Minister Adrian Dix said this week the priority is on getting children their first dose, and that he does not expect the province to deviate from NACI’s recommendation of eight weeks for the second.

Dr. Ladha in Edmonton said parents also have the option of splitting the difference and opting for a five- or six-week interval, potentially decreasing the side effect risk and increasing immune response.

She emphasized the importance of having everyone who is eligible be vaccinated.

“I think the really important point is that children exist in the context of community. If the virus is uncontrolled, if there are uncontrolled COVID outbreaks and high COVID transmission, it impacts children’s schooling, their extracurricular activities, who they can see, their socialization and development,” she said.

“When we talk about protecting the community, that’s essential in actually ensuring children can return to normalcy, and that means that children do need to get vaccinated in order for us to get there.”

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