A new study carried out in Hutterite communities in Canada revealed that giving kids and teenagers flu shots led to lower rates of flu in communities that followed such a strategy compared to similar communities that did not, suggesting that vaccinating children may prevent the virus from spreading and protects members of the community who are not vaccinated, producing a so-called “herd immunity”.
You can read about the study, which was funded by the US National Institute of Allergy and Infectious Diseases (NIAID, part of NIH) and the Canadian Institutes for Health Research, in the 10 March online issue of JAMA. Dr Mark Loeb, of McMaster University, Hamilton, Ontario, led the research.
Flu is a major cause of illness and death that every year kills 36,000 and hospitalizes 200,000 Americans.
At the moment, the US policy is to immunize those at high risk of complications, wrote the authors in their background information (although recently a panel of advisors to the US Centers for Disease Control and Prevention recommended a flu shots for all approach).
The authors argued there could be a case for broadening the policy to use immunization to interrupt spread of the virus in a community, explaining this could protect an entire population, including those at high risk, and since children and adolescents appear to play an important role in spreading the flu, vaccinating this group could be an effective strategy for preventing spread and protecting the non-immunized.
Researchers have already attempted to show that such an approach leads to “herd immunity”, but to build a robust case you need isolated communities so there aren’t others sources of flu coming in.
Loeb and colleagues conducted their investigation in 49 rural Hutterite communities (of the Anabaptist faith) in Alberta, Saskatchewan, and Manitoba in western Canada.
“These tightly knit communities resemble extended families but are composed of single families each residing in their own house, where children and adolescents between the ages of 3 years and 15 years attend school. Approximately 60 to 120 people reside on each colony,” they wrote.
They found that influenza vaccination was 61 per cent effective at indirectly preventing illness in non-immunized people if they lived in a community where about 80 per cent of the children had received flu vaccine.
The researchers designed the study as a cluster randomized trial: thus the communities were randomized so that their children received either the real flu shot (a standard dose of inactivated trivalent influenza vaccine) or a control (which in this case was a hepatitis A vaccine). This allowed the researchers to compare communities where the children had been vaccinated against the flu with communities where they had not.
Overall, the participants involved in the study included the children that received the study vaccine (947 of them, aged from 36 months to 15 years received either the real flu shot or the control, depending on which community they were in), and the other members of the communities (giving a total of 2,326 community members who did not receive either the real flu shot or the control vaccine).
Follow-up began at the end of December 2008, and ended toward the end of June 2009.
The results showed that:
- The average vaccine coverage among healthy children in communities where they received the real flu shot was 83 per cent.
- This was similar to the average vaccine coverage in the control communities where 79 per cent of the healthy children received the control Hep A vaccine.
- Among non-recipients, 3.1 per cent (39 of 1,271) of those in communities whose children received the real flu shot contracted flu (confirmed via lab tests).
- This compares with 7.6 per cent (80 of 1,055) in those communities whose children received the control Hep A vaccine.
- This resulted in an indirect vaccine protective effectiveness of 61 per cent.
- Among all study participants (those who did and those who did not receive the study vaccine) in the communities that had the real flu shots, 4.5 per cent (80 of 1,773 people) had lab-confirmed flu illness.
- This compares with 10.6 per cent (159 of 1,500) total study participants in the communities that had the control Hep A vaccine.
- This resulted in an overall protective effectiveness of 59 per cent.
- The researchers observed no serious adverse events.
The researchers concluded that immunizing children and teenagers significantly protected the non-immunized members of the rural communities.
They wrote this finding is particularly important in the context of the A(H1N1) 2009 pandemic, as it helps us understand the extent to which immunizing children might help prevent rapid spread and thus protect high risk groups such as pregnant women and those found in aboriginal populations.
“Our findings offer experimental proof to support selective influenza immunization of school aged children with inactivated influenza vaccine to interrupt influenza transmission. Particularly, if there are constraints in quantity and delivery of vaccine, it may be advantageous to selectively immunize children in order to reduce community transmission of influenza,” they added.
“Effect of Influenza Vaccination of Children on Infection Rates in Hutterite Communities: A Randomized Trial.”
Mark Loeb; Margaret L. Russell; Lorraine Moss; Kevin Fonseca; Julie Fox; David J. D. Earn; Fred Aoki; Gregory Horsman; Paul Van Caeseele; Khami Chokani; Mark Vooght; Lorne Babiuk; Richard Webby; Stephen D. Walter.
Sources: NIH/National Institute of Allergy and Infectious Diseases, JAMA and Archives Journals.
Written by: Catharine Paddock, PhD