Health Advisory

Second Dose of H1N1 Influenza Immunization is Required for Full Protection among Children 6 Months to 9 Years

To: H1N1 Vaccination Sites
From: Wendy Davis, MD, Commissioner of Health
Date: February 10, 2010

We thank you for your participation in the 2009 H1N1 influenza vaccination program, and remind you that children 6 months through 9 years of age need two doses of vaccine to be fully protected. A second (booster) dose given 28 days or more after initial immunization is needed to achieve optimal protection. If a child received two doses less than 21 days apart, an additional dose should be repeated 28 or more days after the second dose. (If necessary, 21 days or more is still acceptable for this interval.)

The Centers for Disease Control & Prevention (CDC) has received over 250 reports of laboratory-confirmed H1N1 influenza deaths among children in the United States, but estimates are that over 1,100 have actually occurred. Children younger than age 5 have the highest rate of hospitalization than any other age group; school-aged children have the highest rate of infection.

The vaccine against 2009 H1N1 influenza virus is made in the same way as seasonal flu vaccines, with a similar safety profile. Side effects reported have been mild and brief, and similar to those following seasonal influenza vaccine. They include: soreness, redness, or swelling at the injection site; fainting (mainly adolescents); headache; muscle aches; fever, and nausea.

The vast majority of schools in Vermont held school-based immunization clinics for H1N1 influenza. Although first and second dose clinics were held at schools with students  younger than 10 years of age, it is possible that some students received only one dose in the school setting  if they were absent on the day of one of the clinics. All school H1N1 immunizations are entered into the Vermont Immunization Registry. If you are a registry user, you can look up the vaccination status of your patients. If you would like access to the Vermont Immunization Registry, please call 1-888-688-4667 or e-mail

The recent non-safety related voluntary recall and notice of earlier than stated expiration dates for Sanofi-Pasteur vaccine were put in place to ensure that the vaccine used is within its potency specification. There are no safety concerns with these lots of 2009 H1N1 vaccine.  CDC and the Food & Drug Administration are in agreement that the small decrease in antigen content is unlikely to result in a clinically significantreduction in immune response among persons who have received the vaccine. For this reason, there is no need to revaccinate children who have received vaccine from these lots.

There is plenty of vaccine for anyone who would like to be vaccinated against the 2009 H1N1 influenza virus. If you need to order additional vaccine for your practice, call the Immunization Program at 802-863-7638.

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