Immunization Efforts Focus on Adolescents : Teenagers increasingly are being recognized as important reservoirs for certain infectious diseases.

The majority of adolescents and young adults with meningococcal disease are infected with the meningococcal serogroup C, for which vaccine protection is available.

In contrast, infants are generally infected by meningococcal serogroup B, for which there is no vaccine.

Although a polysaccharide meningococcal vaccine (Menomune) has been licensed in the United States since 1978, it was not until the development and FDA licensure of the new quadrivalent conjugate meningococcal vaccine (Menactra) last year that ACIP included it on its list of recommended vaccines for the preadolescent visit.

The conjugate vaccine, approved for use in 11− to 55-year-olds, offers protection against serogroups A, C, Y, and W-135, and it offers improved duration of protection, induction of immunologic memory, booster responses, and reduction in nasopharyngeal bacterial carriage, compared with the polysaccharide vaccine, said Dr. Marchant.

The conjugate vaccine also is recommended for other people at increased risk for meningococcal disease, including college freshmen living in dormitories; microbiologists who are routinely exposed to meningococcal bacteria; U.S. military recruits; individuals traveling to or living in a part of the world where meningococcal disease is common; people who have a damaged spleen or whose spleen has been removed; those with an immune system disorder; and persons who might have been exposed to meningitis during an outbreak.

“We expect the universal immunization recommendation for preadolescents to have a big impact on infection rates,” said Dr. Marchant, noting that universal immunization with the polysaccharide vaccine in the U.S. military significantly reduced meningococcal infections since the immunization policy went into effect, in the early 1970s.

Similarly, a country-wide immunization program with a serogroup C conjugate vaccine in Great Britain (where most of the meningococcal infections among adolescents and young adults have been linked to serogroup C infection) resulted in a significant drop in disease incidence, “suggesting that a conjugate vaccine can control disease,” he said.

An unexpected roadblock to such success with the new conjugate vaccine may be noncompliance with the immunization recommendation resulting from reports of an association with Guillain Barré Syndrome (GBS).

“The immunizations began in the spring of last year, and it came out in September—after 2.8 million doses of the vaccine had been distributed—that there were 6 cases of Guillain Barré that occurred 2–6 weeks post vaccine,” said Dr. Marchant. “While this is more cases than we would like to see, there is not enough evidence to say that this is a cause-and-effect relationship.”

Not only have there not been any further cases reported since that time, there was previous personal or family history of GBS in some of the patients who developed it, further clouding the association, he noted.

“We know that most Guillain Barré is caused by certain infectious agents, but some of these infections are subclinical so we can't get a nice handle on the cause of the cases that occurred.”

Vaccine recommendations are not being altered by these preliminary reports of GBS, Dr. Marchant stressed. “The fact is, GBS has been reported after every vaccine given some time, somewhere, so these few reports are not enough to sway us from stressing the need for protection from meningococcal disease, which has a much higher attack rate and a much higher mortality rate than Guillain Barré Syndrome,” said Dr. Marchant. With respect to the potential for GBS, “we're just going to have to wait and see if it's out there.”

For families who refuse inoculation for their children because of the GBS reports, “it's okay to then recommend the polysaccharide vaccine, with the caveat that it doesn't last as long and may not offer the same protection,” he said.

Human Papillomavirus Vaccine

Although neither of the two human papillomavirus (HPV) vaccines under development—one from GlaxoSmithKline and one from Merck & Co.—have yet to be licensed, infectious disease experts have already begun advocating for their inclusion, upon FDA approval, in the preadolescent immunization lineup.

One of the two vaccines (GlaxoSmithKline's) targets HPV types 16 and 18, which together are responsible for 70% of all cervical cancers. The other vaccine, from Merck, covers these as well as HPV types 6 and 11, which are responsible for approximately 90% of all anogenital warts. “The interesting thing is that types 6 and 11 also cause some abnormal Pap smears, so a vaccine to fight these virus types should also decrease the number of positive Pap smears and procedures that follow,” said Dr. Marchant.

To date, the safety and efficacy of both products in clinical trials looks good compared to placebo, “and the year 2006 has been bandied about as possibilities for licensure,” Dr. Marchant noted. “The most likely scenario will be that these will be added into the 11− to 12-year visit, although there may be some opposition to this from those on the far right.”