A second booster dose of the influenza vaccine in vaccine-naive children may significantly reduce their likelihood of getting the disease, new research suggests.
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Writing for JAMA Pediatrics, researchers reported on a case-control study of 7,533 children presenting to outpatient clinics – all in the U.S. Influenza Vaccine Effectiveness Network – with acute respiratory tract illnesses from 2014 to 2018. The study looked at the effectiveness of vaccination against laboratory-confirmed influenza.
Current U.S. guidelines recommend that children aged 6 months to 8 years receive two doses of the influenza vaccine initially – a priming dose and a booster dose – while those aged 9 years or older are considered to be ‘immunologically primed’ and therefore only require one annual dose.
The study found that 60% of the children had received two doses of the influenza vaccine during their first vaccination season, and 68% were first vaccinated before the current influenza season. Of those who had been vaccinated, 89% had received their first influenza vaccine dose when they were younger than 2 years.
Among the 2,140 children who were unvaccinated before the current influenza season, the 436 children who received two doses of the influenza vaccine had 43% lower odds of influenza compared with the 466 children who received one dose. The overall vaccine effectiveness among this vaccine-naive group aged under 2 years was 38%; for those who received two doses it was 53%, and for those who received one dose it was 23%.
“The higher risk of infection resulting from underdeveloped immune and respiratory tract systems provides a reason to identify vaccination strategies focusing on this vulnerable population of younger children,” wrote Jessie R. Chung, MPH, of the Influenza Division of the Centers for Disease Control and Prevention, and coauthors. “Promoting efforts to improve influenza vaccine coverage—particularly with 2 doses in the first vaccination season – may reduce the burden of influenza illness among young children, who are particularly vulnerable to complications and death from influenza infection.”
Overall 52% of children were unvaccinated for the current influenza season and 9% were partially vaccinated. Of those who were fully vaccinated for the current season, 83% had received one dose in the current season, and 17% had received two doses.
The authors found that full vaccination against any influenza was associated with a 22% lower odds of influenza compared with partial vaccination (95% confidence interval, 0.61-1.01), with partial vaccination defined as anything less than two doses of vaccine in the current season – at least 4 weeks apart – or two or more doses before the current season and one or more doses in the current season. However, even children who were only partially vaccinated still showed statistically significant vaccine effectiveness, except for those who received one dose of vaccine in the current season and were aged under 2 years.
“Compared with older children, young children, even if healthy, are at an elevated risk of influenza infection and influenza-associated complications, such as hospitalization,” the authors wrote. “One recent simulation study reported that even small improvements in either vaccine coverage or VE [vaccine effectiveness], and ideally both, may avert substantial amounts of influenza-associated illnesses, medical visits, and hospitalizations.”
The study also noted that children who had received only a single previous vaccine dose rarely received two doses in the current season.
In an accompanying editorial, Claire Abraham, MD, and Melissa S. Stockwell, MD, of Columbia University Medical Center, New York, wrote that modeling suggested that in the 2017-2018 influenza season, vaccination prevented 1.3 million cases of infection, 895,000 medical visits, 10,500 hospitalizations and 111 deaths in children aged under 5 years.
“This study highlights the importance of administering 2 doses of the influenza vaccine to children younger than 9 years for whom 2 doses are needed, and especially to vaccine naive children younger than 2 years,” they wrote.
But despite many studies showing the impact and importance of influenza vaccination, uptake of this vaccine remained lower than for other pediatric vaccines.
“This present study reemphasizes the need for further research exploring why families who are seemingly willing to vaccinate their children against influenza, as indicated by their receiving the first needed dose of influenza vaccine, find barriers to receiving all of the needed doses, placing their children at higher risk for contracting a potentially devastating virus.”
The U.S. Influenza Vaccine Effectiveness Network is funded by the CDC, and this project also received support from the National Institutes of Health. Eight authors declared grants from the CDC during the conduct of the study, and five declared grants and other funding from private industry outside the study.
SOURCE: Chung J et al. JAMA Pediatrics 2020 May 4. doi: 10.1001/jamapediatrics.2020.0372.