In 2006/2007, the US Advisory Committee on Immunization Practices expanded its recommendations to give the seasonal flu vaccine to children beyond the current target group of 6 months to 23 months of age. However, Canada's National Advisory Committee on Immunization did not, allowing a comparison of vaccination practices between the two countries.

Researchers from the Children's Hospital Boston and Harvard Medical School in Boston, Massachusetts, and McGill University and the Montreal Public Health Department in Montréal, Quebec evaluated the impact of the expanded US policy on influenza-related visits to the emergency department at the Children's Hospital Boston compared with Montreal Children's Hospital. They looked at visits to the emergency department in 2000/2001 through 2008/2009 at the two hospitals.

Of the 1,043,989 visits to the emergency departments of both hospitals for all causes, 114 657 were because of influenza-like illnesses. The researchers analyzed the visits associated with flu-like illnesses and found that "both hospitals had strong seasonal fluctuations in visits related to influenza-like illness in younger age groups, with more subtle seasonal patterns in older pediatric age groups and similar seasonal epidemic increases, declines and peak timing of the epidemic curve," write Drs. John Brownstein and Anne Hoen, Children's Hospital Boston, with coauthors.

"Following the policy change in the United States, we observed a decline in the rate of emergency department visits for influenza-like illness at Children's Hospital Boston relative to the Montreal Children's Hospital in the target age group, children two to four years old," they state.

They also saw declines of 11%-18% in other nontarget age groups (ages 0-1 year, 2-4 years, 5-9 years and 10-18 years), which may be related to an overall reduction of influenza in transmission at home and in the community because of vaccination of two to four year olds.

"A number of factors influencing the observable trends in our data sets may be independent of the policy shift that was of interest for our study. Nonetheless, our findings provide evidence that, in our US study community (i.e., Boston), the recommendation of the Advisory Committee on Immunization Practices to routinely vaccinate preschool-aged children against seasonal influenza is improving pediatric influenza-related outcomes," conclude the authors. They suggest that adopting a similar policy in Canada would be effective at reducing influenza-related illness.

In a related commentary Dr. Ville Peltola and coauthors from Turku University Hospital, Turku, Finland, write: "Although children younger than two years, elderly adults, pregnant women and people with chronic illnesses are well-defined risk groups for severe influenza, children of other ages and healthy adults would also benefit from influenza vaccinations in the form of decreases in outpatient visits, antibiotic and antiviral consumption, absenteeism from school and jobs and, to a lesser degree, hospital admissions and deaths. Expansion of vaccinations should also have beneficial effects at the population level, because vaccinated people do not transmit influenza viruses further."

Note: If no author is given, the source is cited instead.

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