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From the CMAJ (Canadian Medical Association Journal) we get the results of a comparative study between the United States – which expanded its recommendations for seasonal influenza vaccination to include healthy children aged 24–59 months in 2006-07, and Canada which did not follow suit.
Using data collected on ER visits by children in two pediatric hospitals located in Boston, Massachusetts & Montréal, Quebec over a period of 9 years, they were able to compare the rates of influenza-like-illness (ILI) among children both before and after the U.S. vaccine policy change went into effect.
What they found was that relative to Canada, the U.S. saw a 34% reduction in ILI among children aged 2-4 since the new vaccine recommendations were instituted.
The research paper is available on the CMAJ website:
Effect of expanded US recommendations for seasonal influenza vaccination: comparison of two pediatric emergency departments in the United States and Canada
Anne Gatewood Hoen, PhD, David L. Buckeridge, MD PhD, Katia M.L. Charland, PhD, Kenneth D. Mandl, MD MPH, Caroline Quach, MD MSc, John S. Brownstein, PhD
Interpretation: The divergence in influenza rates among children in the US and Canadian sample populations after institution of the US policy to vaccinate children two to four years of age is evidence that the recommendation of the US Advisory Committee on Immunization Practices resulted in a reduction in influenza-related morbidity in the target group and may have indirectly affected other pediatric age groups. Provincial adoption of the 2010 recommendation of the National Advisory Committee on Immunization in Canada to vaccinate children two to four years of age might positively affect influenza morbidity in Canada.
For more details, we get this press release from Children’s Hospital in Boston.
'Natural experiment' documents the population benefit of vaccinating preschoolers against the flu
Flu rates among two- to four-year-olds decline 34 percent following changes in U.S. vaccine policy; study is first to use real time hospital data to evaluate policy change
Boston, Mass. – Recent policies calling for vaccinating preschool-aged children against the flu led to a 34 percent decline in influenza cases in this age group, according to researchers at Children's Hospital Boston and McGill University. The findings, which revealed smaller declines in other age groups as well, arose from a study that used real time surveillance data from pediatric emergency departments (EDs) in the United States and Canada to evaluate the relationship between national flu vaccination policies and rates of flu-like illness.
The research team, led by Anne Gatewood Hoen and John Brownstein of the Children's Hospital Informatics Program (CHIP), reported their findings September 19 in the Canadian Medical Association Journal.
Preschoolers – specifically children aged two to four – play a significant role in community transmission of the flu with each new season. The Advisory Committee on Immunization Practices – the national body that sets vaccination policies in the U.S. – updated its influenza vaccine recommendations in 2006 to include vaccination of this age group. The corresponding Canadian body, the National Advisory Committee on Immunization, did not include these children in its recommendations until 2010.
"The differences in the U.S. and Canadian policies created conditions for a natural experiment for evaluating the effects of U.S. policy change in the target age group," said Brownstein, director of CHIP's Computational Epidemiology Group. "They also gave us an opportunity to test whether we could use hospital-based real time surveillance data to assess the effects of policy changes, and do so more quickly than traditional epidemiologic studies, which are more focused on vaccine uptake than on outcomes."
As always, there were some limitations to this study. First, it was only conducted at two hospitals, which might not accurately reflect national trends.
Second, that influenza diagnoses were rarely confirmed by lab tests, but were rather based on symptoms of ILIs (influenza-like-Illnesses). The authors state, however, that:
Repeating our analysis with a narrower definition of influenza-like illness resulted in a strengthening of the effect from a 34% reduction to a 52% reduction in emergency department visits for influenza-like illness at Children’s Hospital Boston relative to the Montreal Children’s Hospital, which suggests that our broad definition resulted in a conservative estimate of the effect.
And third, data on vaccine uptake for each patient was not generally available, and instead the authors relied upon surveys of vaccination rates among children during the years in question.
Still, despite these limitations, this study provides strong evidence to support to the policy of vaccinating young children against seasonal influenza.
With influenza season soon upon us, the CDC would like to see just about everyone over the age of 6 months get the flu vaccine.
For details on this year’s recommendations see:
MMWR: ACIP Updated Flu Vaccination Recommendations
The CDC also provides a parent’s guide with information on the danger signs in children, and advice on vaccination.
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