TABLE 2
Contraindications to influenza vaccine
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The thimerosal controversy
Family physicians are likely to encounter questions from parents or guardians about thimerosal in influenza vaccines. Thimerosal is a preservative containing mercury, which has been used in vaccines for more than 70 years. Because of the increasing number of recommended childhood vaccines and the resulting cumulative exposure to mercury, there has been a concerted effort since 1999 to reduce the content of thimerosal in vaccine products.
Almost all vaccines are now free of thimerosal. However, inactivated influenza vaccine distributed in multidose vials does contain thimerosal, 12.5 μg mercury/0.25 mL dose. Single-dose vials containing inactivated influenza vaccine do not contain thimerosal as a preservative, but this product still contains trace amounts of mercury, <0.5 μg/0.25 mL dose.
No evidence has shown conclusively that mercury-containing vaccines cause serious adverse effects. A recent Institute of Medicine report concludes that the weight of evidence supports a lack of causation between thimerosal and autism.7 Nevertheless, many parents remain concerned about mercury exposure from vaccines. Reassure those who are concerned that the cumulative exposure to mercury from all vaccines has decreased markedly and that influenza vaccine contains only low amounts of thimerosal. Those wishing to decrease this risk even further should be given the option of the single-dose vial product, if available.
Timing vaccination for optimal protection
The influenza season varies year to year but normally occurs between November and March. Vaccination for those at high risk of influenza complications, including those aged 6 to 23 months, should begin in September and October. Those who need 2 doses should receive the second by December if possible.
Because of the length of the influenza season and the fact that the inactivated influenza vaccine is not approved for use during the first 6 months of life, infants will become eligible for the vaccine at different points in the influenza season. Office procedures should be implemented to identify eligible infants as the season progresses and to notify parents or guardians of the opportunity to vaccinate their infant.
If an infant enters the 7th month of life late in the influenza season and vaccine is still available, vaccination should still be considered, not only to offer protection in the current year but also to reduce the number of doses needed the next year. In instances when only 1 dose of a recommended 2-dose schedule is completed, only 1 dose is needed the following year.
Vaccinate close contacts of infants and children
The new ACIP recommendations state that persons who can transmit influenza to those at high risk of complications should also be vaccinated. This includes household contacts of, and those who provide care to, children aged <2 years.
For infants in their first 6 months of life, preventing infection among close contacts is the major preventive intervention available. The Vaccine for Children program now includes influenza vaccine for members of households (those who are aged <18 years) where children aged <2 years live.
Vaccine complications and contraindications
Local reactions including redness, pain, and swelling are common after influenza vaccine administration. Generalized reactions including fever, malaise, and myalgia are less common and can start within 6 to 12 hours and last 1 to 2 days. Contraindications to vaccine administration are few (Table 2).
When chemoprophylaxis is an option
Only 2 options exist for chemoprophylaxis against influenza in children before their 13th birthday: amantadine and rimantadine. The dosage for each is 5 mg/kg/d, up to 150 mg, in 1 or 2 doses. Both are effective only against influenza A and are approved for use only after the 1st birthday. Still, this option should be kept in mind for unvaccinated children who are exposed to influenza.
A chemoprophylactic agent can be started at the same time the vaccine is administered. Since it takes 2 weeks to develop protective levels of antibodies, chemoprophylaxis should be continued for 2 weeks with those who need only 1 vaccine, and until 2 weeks after the 2nd vaccine for those who need 2 doses.
Update: Anticipated shortage of vaccine in fall of 2004
In early October, 1 of the 2 producers of inactivated influenza vaccine for the United States market, Chiron Corporation, had its license suspended by the Medicines and Healthcare Products Regulatory Agency (MHRA) in the United Kingdom, where their plant is located. This will cause a shortage of vaccine, since Chiron was to have supplied about half of the 100 million doses planned for this country.
Chiron, however, was not a producer of vaccine for children aged <4 years. Based on this anticipated shortfall, the ACIP is recommending that the vaccine be given preferentially to those at high risk for influenza complications ( Table 3 ) and that those who are not in one of these categories forgo vaccination. Physicians who will not have an adequate supply of vaccine for their patient population are encouraged to have their priority patients seek vaccine at another location.