Vaccine Policy Change Significantly Reduced Flu Rates for Preschoolers

A 2006 change in US vaccination policy for preschoolers led to a significant decline in flu cases for children in all age groups, a study finds.

A change in US policy calling for vaccination of preschool-aged children against the flu led to a significant decline in flu cases in the age group, as well as among children in other age groups, a study published yesterday in the Canadian Medical Association Journal finds.

In 2006, the Advisory Committee on Immunization Processes, which sets vaccination policy for the US, recommended flu vaccination for children aged two to four. The analogous Canadian organization, the National Advisory Committee on Immunization, did not include the same age group in its recommendations until 2010.

The differing policies set up a “natural experiment” that allowed researchers to quantify the effects of the policy change. To do so, they looked at 114,657 visits for flu-like illness (out of 1,043,989 total visits) to the pediatric emergency departments (ED) at Children’s Hospital Boston and Montreal Children’s Hospital from 2000 to 2009, including years when the countries' flu vaccination policies for preschoolers were the same and years when they differed.

After accounting for demographics and epidemiological dynamics, the researchers determined that the rate of visits by two- to four-year-olds with flu-like symptoms to the Boston hospital ED declined 34% compared with the ED of the Montreal hospital after the 2006 US policy change. In addition, the researchers found that the number of children in other age groups visiting the Boston ED declined 11% to 18% compared with the Montreal hospital.

"There are a few explanations for the findings in other age groups," said study co-author Anne Gatewood Hoen, a research fellow at the Children’s Hospital Informatics Program, in a press release. "It could be that vaccinating preschoolers reduced the spread of the virus in the home and the community, kind of a 'herd immunity' effect. It is also possible that the policy change had the side effect of improving vaccine uptake overall by promoting general awareness of the benefits of vaccinating children overall, or by increasing the likelihood that parents would get the siblings of preschoolers vaccinated."


'Natural experiment' documents the population benefit of vaccinating preschoolers against the flu [Children’s Hospital Boston Press Release]