The H1N1 vaccine will start arriving in pediatricians’ offices this week, and we suddenly felt panicked about having to make a decision: to inoculate or not to inoculate? So we fired off a bunch of questions to our trusted MD Moms, who came back with a fantastically thorough explanation of all the issues surrounding the Swine Flu shot.

Here, everything a mom could possibly want to know about the new H1N1 vaccine:

When will the vaccine be available? According to the CDC, the first 7 million doses of H1N1 vaccine are shipping this week. Another estimated 60-195 million doses are anticipated to ship over the next few months, in weekly batches. Currently, we have no information as to where the first doses will be shipped. The best strategy is to watch your local news and keep abreast of notices posted or sent by your health care provider.

Will there be enough to meet demand? Hopefully, yes—especially as it pertains to high-risk individuals. The first groups who will be targeted for immunization are: household members and caregivers of babies under 6 months of age; children 6 months-4 years of age; children 5-18 years of age with high-risk health conditions (asthma, lung disease, sickle cell anemia, heart disease, chronic kidney disease, immune compromise, chronic aspirin therapy, blood diseases, neuromuscular diseases, diabetes, and HIV); pregnant women; adults with high-risk health conditions; health-care workers; very obese individuals (BMI >35); and elderly individuals living in nursing homes and assisted-living facilities.

What are the differences among the four versions of the vaccine? Currently four manufacturers have been producing H1N1 vaccine; three are producing shots, and one is producing a nasal spray. All have applied the same stringent manufacturing standards and processes used for production of regular seasonal influenza vaccines.

  • CSL Brand: FDA-approved for individuals 18 years of age and older
  • Novartis Brand: FDA-approved for people 4 years of age and older. There are two forms of this shot: multi-dose vials (with Thimerosal used as a preservative) and pre-filled single-dose syringes (with Thimerosal used in the manufacturing process, but extracted before the final production)
  • Sanofi Brand: FDA-approved for children 6 months of age and older. There are two forms of this shot: multi-dose vials (Thimerosal-free) and pre-filled single-dose syringes (Thimerosal-free)
  • Medimmune: FDA-approved nasal spray for individuals 2-49 years of age (Thimerosal-free)


Should I worry if my child can only get a Swine Flu shot that uses Thimerosal? Thimerosal is a preservative that has been used since the 1930s to prevent contamination in some multi-dose vials of vaccines (preservatives are not required for vaccines in single-dose vials). Thimerosal contains approximately 49% ethylmercury, which is often confused with methylmercury (found in sushi and large pelagic fish such as halibut, swordfish and tuna). The kidneys excrete thimerosal very effectively, while methylmercury is fat-soluble and more likely to be absorbed by its host.

There is no convincing evidence of harm caused by the low doses of Thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site. However, in July 1999 the Public Health Service (PHS) agencies, the American Academy of Pediatrics (AAP), and vaccine manufacturers agreed that Thimerosal should be reduced or eliminated in vaccines as a precautionary measure.

Thimerosal-free influenza vaccines are available, but in limited quantities. (Availability will improve as manufacturing capabilities are expanded.) Priority for Thimerosal-free vaccine will be given to pregnant women and children. However, if the only flu vaccine available for administration is one in which Thimerosal was either used in manufacturing or a tiny amount in the final product, it is still a good idea to get the vaccine. To date, there is still not any substantial proof that Thimerosal is harmful in any way.

Are there any other controversies around the vaccine and its ingredients? The H1N1 vaccine does not contain any aluminum or other adjuvants (products that increase a body’s response to a vaccine). Other countries have used adjuvants since 1997, but U.S. manufacturers have never done this. The H1N1 vaccine (in all forms) is adjuvant-free.

Many parents have come to us with concerns that the H1N1 vaccine may cause Guillain-Barre syndrome (GBS). This has certainly been a hot topic on the Internet. It’s worth a little extra reading on the CDC website to set the record straight.

Is it a one-shot dose, or is a booster required? Children under the age of 10 will need two doses, given one month apart. This pertains to both the H1N1 shot, as well as the mist preparation. Think of the first dose as “priming” the immune system, and the second one as “activating” the child’s immunity. One dose will not protect a child who is 6 months to 9 years of age. Anyone over the age of 10 will only need one dose of H1N1 vaccine.

How do I choose between the shot and the nasal spray form? The mist form of H1N1 is a live-attenuated vaccine, and is Thimerosal-free. It is FDA-approved for healthy people 2-49 years of age. If your child does not have a history of asthma, recent wheezing, or a high-risk health condition, the mist form of H1N1 vaccine is a non-painful option for your child. The downside might be a day or two of sore throat, sniffles, and/or a low-grade fever. Live virus preparations typically activate a different arm of the immune system, and may result in more prolonged immunity. The H1N1 pandemic vaccine in mist form is free, however, your health care provider will likely charge an “administration fee” to cover the cost of staff time, disposal of syringes, and administrative time necessary to obtain vaccine.

Note: Pregnant women and children under the age of 2 SHOULD NOT receive the mist form of H1N1. Neither should individuals with severe/anaphylactic reaction to egg or components of the vaccine (gentamicin, gelatin, or arginine); people with asthma or active wheezing; children under 5 years of age with recurrent wheezing; people with immune deficiencies; people with underlying medical conditions that may be aggravated by live vaccine (always check with your health care provider); people with extremely stuffy, congested noses (as absorption of the vaccine may not occur); children or adolescents on chronic aspirin therapy.

Are there any possible side effects caused by the vaccine? Typical reactions to the H1N1 vaccine are anticipated to be the same as those experienced with regular seasonal flu vaccine. For the shots, these include possible pain or soreness at the injection site, muscle ache, headache, low-grade fever (usually for a day or two), fainting (usually in adolescents), and, rarely, allergy to one of the components of the vaccine. For the nasal mist preparations, nasal congestion and stuffiness are fairly common for a few days after administration, in addition to possible low-grade fever, muscle aches and fatigue.

How has the vaccine done in clinical trials? Two different 2009 H1N1 influenza vaccines have been enrolled in clinical trials as of July, 2009: one developed by Sanofi Pasteur in Swiftwater, Pennsylvania, and the other by CSL Limited in Melbourne, Australia. Initial review of the data involving more than 500 healthy adult volunteers showed both vaccines to be safe and effective. Because of these positive results, clinical trials began on children on August 18, 2009, using the Sanofi H1N1 vaccine.

The pediatric trials have involved eleven medical centers nationwide; more than 1,200 children between the ages of 6 months and 17 years have been administered the H1N1 vaccine. Preliminary results published on September 21, 2009 showed that an effective immune response was seen in the majority of 10-17 year-olds within eight-to-ten days of receiving the vaccine.  Younger children generally had a weaker early response to the vaccine. Current ongoing studies are addressing whether there is a dose:response relationship with the vaccine (i.e., is giving more of the vaccine going to yield better or longer immunity?). In addition, the effectiveness of combining seasonal influenza vaccine with 2009 H1N1 vaccine is being examined.  Data will be updated as it comes in from the National Institutes of Allergy and Infectious Diseases (NIAID) and from the National Institute of Health (NIH).

Should my child get both the seasonal flu vaccine and the H1N1 vaccine? Yes, it’s a good idea to protect your child from all threatening strains of flu this year. Both seasonal flu shots and H1N1 shots can be given on the same date, and if a repeat dose is needed, those doses can be given together as well.  The only tricky part here is that a child cannot receive protection from two mist preparations on the same day. So a parent has the prerogative to opt for one shot/one mist.  If you only want your child to receive flu protection in mist form exclusively, you must separate all those doses by four weeks—thus stretching out immunization over four months and possibly delaying the timely administration of second doses, if required. Also, keep in mind that if your child has had any other live virus vaccine (i.e., MMR, Chicken Pox, or Rotavirus vaccine) within the last month, you should wait four weeks after that vaccine before administering any flu vaccine.

Note: Most health care providers already started administering regular seasonal flu vaccine in early September. Unfortunately, full production and shipments of vaccine to all health care entities were held in order to produce H1N1 vaccine. As a result, your health care provider may be awaiting shipment of more regular seasonal flu vaccines (especially preservative-free formulations), and all any of us can do is wait patiently for the remainder. 

After what date is it too late to get the H1N1 vaccine? Peak flu season varies across the U.S. On the east coast and in northern regions, flu season peaks around the holidays, whereas on the west coast and in southern regions, it often peaks as late as February.  Unfortunately, since H1N1 novel strain seems to know no “season” (having surged in the spring, quieted a bit in summer, and now ramping up again) anytime is appropriate—but the earlier, the better. What we have yet to learn is whether we will need to have repeat inoculations more than once yearly, given the propensity of H1N1 to occur year-round (as typical influenza vaccines generate only 4-6 months of immunity).

 —Diane Truong, MD and J.J. Levenstein, MD