Medical Letter consultants have brought to our attention some confusion that has accompanied the release of Adacel, a combination of tetanus toxoid, diphtheria toxoid and acellular pertussis antigens (Tdap) recently approved for use as a booster in adolescents and adults 11-64 years old (Med Lett Drugs Ther 2006; 48:5). Another Tdap vaccine, Boostrix, is approved for use in adolescents 10-18 years old. Some adults have inadvertently been immunized with Daptacel or Infanrix (DTaP), which are intended for active immunization of infants and children 6 weeks to 6 years old. Such mix-ups were reported by the Institute for Safe Medication Practices (www.ismp.org) in the August 24 and December 2006 issues of its newsletter.

The problem with giving these pediatric vaccines to adults is that they contain more diphtheria and pertussis antigens than the adult vaccine, and adults may have untoward reactions to these higher antigen levels. One consultant who inadvertently gave the pediatric vaccine to 80 adults reports that a few developed fever to 102ºF, and several developed severe erythema and swelling at the injection site. In the absence of a comparative trial, whether these reactions were due to the higher antigen load can only be a matter of speculation.

The reasons for the mix-ups, according to the Institute, include the similarities in the brand names and packaging of Adacel and Daptacel in addition to the similar component antigens in the 2 products (the components of Adacel are listed in a different order and are labeled as “reduced” diphtheria toxoid and acellular pertussis). The manufacturer of Adacel and Daptacel intends to make changes in the packaging and labeling to clarify the differences between the products. The inadvertent administration of Infanrix to adults was caused by an electronic order entry program’s failure to differentiate between the adult and pediatric vaccines.

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Since the publication of our article on influenza vaccine (October 9, 2006), a fourth inactivated vaccine (FluLaval - GlaxoSmithKline) has been approved by the FDA for use in people ≥18 years old. It is sold in 5-mL multi-dose vials. Each 0.5-mL intramuscular dose contains 25 mcg of mercury.

Annual immunization against influenza A and B is the most effective method of preventing infection and has been shown to reduce associated complications.

The US Advisory Committee on Immunization Practices (ACIP) has recommended the addition of a routine second dose of varicella vaccine for children <13 years old. Varicella vaccine has been used in the US since 1995, but varicella outbreaks have continued to occur among school children vaccinated with a single dose. In one such outbreak, the attack rate was 100% in unvaccinated children and 18% in those previously vaccinated.1 In vaccinated children, the typical maculopapular-vesicular rash of varicella may be only maculopapular with few or no vesicles, but these children could still transmit virus to susceptible contacts.

A live attenuated varicella-zoster vaccine (Zostavax - Merck) has been approved by the FDA for prevention of herpes zoster (HZ; zoster; shingles) in persons ≥60 years old. Each dose of Zostavax contains about 14 times as much varicella-zoster virus (VZV) as Varivax, which has been used in the US since 1995 to vaccinate against varicella (chicken pox).

A recombinant quadrivalent human-papillomavirus-like particle vaccine, Gardasil (Merck), has been approved by the FDA for use in girls and women 9-26 years old to prevent diseases associated with infection with human papillomavirus (HPV) types 6, 11, 16, and 18, including genital warts, precancerous cervical, vaginal or vulvar lesions, and cervical cancer.

The FDA has recently approved RotaTeq (Merck), an oral live, human-bovine reassortant rotavirus vaccine, for use in infants to prevent rotavirus gastroenteritis, a frequent cause of severe diarrhea in infancy.

Although immunization programs have produced high vaccination rates in US infants and children, similar successes have not been achieved in adults. Vaccines recommended for routine use in adults are reviewed here. Immunizations for travel were reviewed in a recent issue.

A large mumps outbreak that began in Iowa in December 2005 has spread. About 40% of the cases have been in people 18-25 years old, many of whom are college students and had been vaccinated against the disease.

Patients planning to travel to other countries often ask physicians for information about immunizations and prevention of diarrhea and malaria. More detailed advice for travelers is available from the Centers for Disease Control and Prevention at 877-FYI-TRIP (877-394-8747) or www.cdc.gov/travel.

The FDA has licensed Adacel (Aventis Pasteur) and Boostrix (GlaxoSmithKline), two new combination vaccines that include tetanus toxoid, diphtheria toxoid and acellular pertussis antigens (Tdap), for use as a booster in adolescents and adults. In the past, older children and adults were not re-immunized against pertussis because of concerns about reactions to the whole-cell vaccine previously used in younger children. The CDC Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) have recommended that either of the new Tdap vaccines replace routine tetanus-diphtheria (Td) boosters in adolescents 11-18 years old, and Adacel should replace Td boosters in adults 19-64 years old.

Antiviral prophylaxis is indicated for influenza exposures that occur before (or less than 2 weeks after) vaccination with inactivated vaccine, or in years when circulating strains differ from those included in the vaccine. Antiviral drugs can also be used for treatment of patients who develop symptoms of influenza, regardless of vaccination status.
Please see Update: Influenza Resistance to Amantadine and Rimantadine