KANSAS CITY, MO. — The strategy of immunizing all children at the 11- to 12-year preadolescent visit and those entering high school with the new meningococcal conjugate vaccine appears to be working, according to preliminary Centers for Disease Control and Prevention data.
Uptake of Menactra vaccine was higher in these target age groups compared with nontargeted 13- and 16-year-olds in a study of 619,371 adolescents, Dr. Pascale Wortley and associates reported at the National Immunization Conference sponsored by the Centers for Disease Control and Prevention.
Menactra (made by Sanofi Pasteur) was licensed in January 2005 for use in persons aged 11–55 years, and is recommended for all children at the 11- to 12-year preadolescent visit, those entering high school, college students living in dormitories, U.S. military recruits, and others who choose to be vaccinated.
The study also indicated that heavy demand during the summer months did cause a vaccine shortage.
“Even though the total number of teens vaccinated did not exceed the amount of vaccine available, because it was all concentrated over the space of a few months, it did create a shortage situation,” said Dr. Wortley of the CDC's Immunization Services Division in Atlanta.
The investigators analyzed data from 619,371 adolescents aged 11–16 years vaccinated with Menactra (MCV4) in 2005 at five of eight managed care organizations participating in the Vaccine Safety Datalink.
The five managed care organizations experienced a rapid increase in immunizations among the three age groups (11–12 years, 14–15 years, and 13- and 16-year-olds) between May and August, followed by a rapid decline to a relatively steady rate by Sept. 30. Overall, 73% of vaccinations were given between June and August, said Dr. Wortley, who presented the results on behalf of lead author Dr. Suchita Lorick, also of the CDC in Atlanta.
At the end of 2005, the cumulative coverage was 12% for ages 11–12 years, 11% for ages 14–15 years, and 8% for ages 13 and 16 years.
Compared with the group of 13- and 16-year-olds, the risk ratios for receiving Menactra for those aged 11–12 years and 14–15 years were 1.49 and 1.29, respectively.
Coverage among 11- to 12-year-olds reached nearly 35% at one of the HMO sites with an explicit policy targeting this age group, compared with less than 15% at two other larger HMO sites that reported experiencing some degree of vaccine shortage in 2005, she said.
Because of the strong summer usage, the investigators decided to compare Menactra uptake patterns with uptake for the old polysaccharide meningococcal formulation (Menomune, also made by Sanofi Pasteur) and the tetanus and diphtheria (Td) vaccine. They used data from the 2003–2004 Vaccine Safety Datalink and 2004 data from the MarketScan databases, representing 40 self-insured employers and more than 1 million 11- to 16-year-olds.
All three vaccines experienced increased usage during the summer, which comes as no surprise given the number of school physical examinations conducted at this time of year, Dr. Wortley said.
The September decline observed in Menactra usage likely was not related to the Food and Drug Administration's and CDC's notice in October 2005 that Guillain-Barré Syndrome could be associated with Menactra, she added.
“Clearly, vaccination had already decreased dramatically before that notice appeared,” Dr. Wortley said. “It looks like the uptick was related to the ACIP [Advisory Committee on Immunization Practices] recommendation, and potentially, the trend down was not related to the [Guillain-Barré Syndrome] notice.”
The CDC's Advisory Committee on Immunization Practices published its recommendations for Menactra in May 2005 after debating the age group or groups for which the vaccine should be recommended. Older adolescents (17–18 years) have the highest rates of meningococcal disease (1.7 per 100,000). But younger teens, who have somewhat lower rates of infection, are more likely to visit their physicians through the already established preadolescent health care visit and high school-entry physical examination.