Tuesday, October 27, 2009

H1N1 swine flu vaccination in children

Parents are concerned about the best way to protect their children, and are asking whether to vaccinate them. Parents have to make their own risk/benefit decisions. I hope the following is helpful:

1. Do you feel comfortable enrolling your child in clinical trials? At this point in time, the swine flu vaccine program in children is equivalent to a clinical trial. The only published study of any swine H1N1 vaccine in children is from China, and we don't know if their data can be extrapolated to other countries.

2. Safety data from the China study are rudimentary, and efficacy was assessed only with antibody levels. So, for that vaccine (similar but not identical to vaccine used in the US, Canada and Europe) we lack information on how well it prevents cases of flu. Experts don't even know if one or two shots are needed for children under 10. As of October 31, the WHO's Strategic Advisory Group of Experts acknowledged that data on that age group was "limited and more studies are needed."

3. In adults, the best level of protection from seasonal flu vaccines (when the vaccine strains are a good match to circulating flu viruses) is about 70%. Younger children do not achieve this high a level of protection. A rough estimate for the amount of protection you should expect from the vaccine, assuming it works well, is a 50% to 70% reduction in swine flu infections.

studies sponsored by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), 8 to 10 days after receiving a 15 microgram dose of an inactivated vaccine that contains proteins from the novel H1N1 virus, 76% of the older children had a “robust” antibody response. But in those children between 3 and 9 years old, the same immune response was only seen in 39% of vaccinated kids, and it dropped to 25% in children 6 to 35 months.

4. If vaccinating, avoid injected vaccines that contain thimerosal (50% mercury).

5. We don't yet know if the live swine flu vaccine will be virulent for people with immune compromise. If your child will be in contact with others on cancer chemotherapy, high dose steroids, radiation therapy, etc., I would avoid live vaccines.

6. There is no published information about the safety or effectiveness in children of any live (inhaled) swine flu vaccines at this time.

7. The Canadian vaccine package insert states, "There is very limited experience with AS03-adjuvanted H5N1 vaccine in children between 3 and 9 years of age, and no experience in children less than 3 years of age or in children and adolescents between 10 and 17 years of age."

8. One US vaccine's (Sanofi-Adventis, used at my institution) package insert indicates that adverse reactions to one flu vaccine were evaluated in 2003-4 in (only) 31 children aged 6 through 36 months, and (only) for 3 days after each of two doses. Clearly these data provide little useful information. There isn't much more for older age groups.

9. I found it interesting to learn (in Science magazine) that only 3 countries recommend seasonal flu vaccinations in children: the US, Mexico and Finland.

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