Longer interval between COVID-19 vaccine doses could improve protection
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A longer interval between doses of COVID-19 vaccine in children aged 5 to 11 years was associated with higher effectiveness against symptomatic infection, according to a real-world study published in Pediatrics.
Pierre-Philippe Piché-Renaud, MD, a physician in the division of pediatric infectious diseases at the Hospital for Sick Children in Toronto, said that although most children with COVID-19 do not need to be hospitalized, some do, and the “vast majority of children who are coming in the hospital for COVID-19 are unvaccinated.”
“Since the beginning of the vaccine rollout, we've had interest in looking at vaccine effectiveness in different age groups,” Piché-Renaud told Healio. “We felt that we needed more information on duration of protections of vaccines in 5- to 11-year-old children, and especially looking at differences in in effectiveness when there were varying dosing intervals.”
Dose intervals are the “principal characteristic” differentiating this study’s findings from other studies on the subject, he said. In Canada, children were allowed either a 3- or 8-week interval between doses.
“We wanted to evaluate the differences between effectiveness in these different regimens,” Piché-Renaud said.
The researchers used provincial databases to study the effectiveness of the Pfizer-BioNTech vaccine against infection and severe outcomes between Jan. 2 and Aug. 27, 2022, in Ontario. The data included 6,284 test-positive cases and 8,389 test-negative controls.
The researchers found that vaccine effectiveness against symptomatic infection was 24% (95% CI, 8%-36%) 14 to 29 days after a first dose and 66% (95% CI, 60%-71%) 7 to 29 days after two doses.
Effectiveness was higher for children with dosing intervals of 56 days or longer (57% [95% CI, 51%-62%]) compared with 15 to 27 days (12% [95% CI, 11% to 30%]) and 28 to 41 days (38% [95% CI, 28%-47%]) but did wane over time for all groups.
Effectiveness against more severe outcomes was 94% (95% CI, 57%-99%) 7 to 29 days after two doses and declined to 57% (95% CI, 20% to 85%) after 120 or more days.
“What we did find in our study is that there was sustained protection in the first few months after the second dose of the vaccine,” Piché-Renaud said. “Starting at 4 months after the second dose of the vaccine, this is when we saw significant waning of the protection.”
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