CAMBRIDGE, MASS. — Much of the “action” in the immunization arena is shifting to adolescents, according to Colin Marchant, M.D.
“Adolescent immunizations are a quickly evolving area, as youth in this age group are increasingly being recognized as important reservoirs for certain infectious diseases,” Dr. Marchant said at a pediatric infectious disease meeting sponsored by Boston University School of Medicine, PEDIATRIC NEWS, and FAMILY PRACTICE NEWS.
Until recently, the universal immunization recommendation for the 11− to 12-year preadolescent visit was for a diphtheria-tetanus (DT) booster. Earlier this year, the Center for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) added the acellular pertussis and the conjugate meningococcal disease vaccines to its list of recommended immunizations for adolescents.
And it is likely that another vaccine—one of the two human papillomavirus vaccines currently wending their way through safety and efficacy trials—will be added to the adolescent immunization roster as soon the Food and Drug Administration approves them for use, said Dr. Marchant of Boston University.
It is expected that these vaccines will significantly reduce the infection rates of the respective diseases not only among adolescents, but also among infants and immunocompromised individuals in close contact with the adolescents, Dr. Marchant noted.
Acellular Pertussis Vaccine
With respect to pertussis, “adolescent immunization, and in fact adult immunization, is our unfinished business,” said Dr. Marchant, referring to the rise in recent years of pertussis infections.
In 2004, the highest number of U.S. pertussis cases was among individuals 10–18 years of age, with roughly 6,500 cases reported, according to data from the Centers for Disease Control and Prevention. Looking at infection rates across different age groups, “the numbers have remained steady for children ages 1–10, but they increase substantially starting at age 11 and peak around age 15, then start to fall back down,” he said.
“It's no surprise that kids in the adolescent age range have high rates of infection. They have lower antibody levels because their last pertussis immunization was before their 7th birthday.
“By age 11 or so, the vaccine-related antibody levels will have gone down, leaving these kids vulnerable to infection,” said Dr. Marchant.
Because these children are in such close contact with other children, in school and on sports teams, it's likely that once they're exposed to pertussis, they're going to get sick, because the infection is so highly contagious, with an airborne spread and from contact with nasal secretions, he said.
The observed rise in antibody levels after age 15 can be attributed to immunity developed through infection.
“We've known all along that immunity to pertussis wanes, but it wasn't until the late ′80s that we started going around looking for and counting cases of pertussis,” Dr. Marchant stated. With the 1987 introduction of the single-serum blood test to determine pertussis antibody levels, “we began to document cases, and as always, the closer you look, the more you find.”
In 2001, a pertussis outbreak in a youth football team in Arkansas led to 77 documented cases of the disease, forcing a school closure.
Around the same time, 500 cases (median age 13) were documented in a community in Arizona.
In 2003–2004, an outbreak traced to a high school weight room in Wisconsin led to 300 documented cases, primarily among adolescents, but also including some among infants, “who presumably were infected by adolescents or adults and who required hospitalization,” said Dr. Marchant.
These and other outbreaks have led to an increased public awareness of the spread of pertussis infection and have also led to stepped-up efforts to protect adolescents and adults from infection and to minimize the risk of disease transmission to infants, who experience significantly more morbidity and mortality as a result of infection.
In June of this year, with data from large, multicenter trials showing the two tetanus, diphtheria, acellular pertussis vaccines that were recently approved (GlaxoSmithKline's Boostrix and Sanofi Pasteur's Adacel) for use in adolescent and adult populations, ACIP recommended that all adolescents get the pertussis-inclusive vaccine instead of the TD-only booster at the 11− to 12-year visit.
In October of this year, the committee further recommended that adults also receive the pertussis vaccine the next time they are due for a booster, said Dr. Marchant.
Conjugate Meningococcal Vaccine
Life-threatening meningococcal disease affects 1,400–2,800 individuals in the United States each year. While the incidence is highest in children younger than 2 years, adolescents and young adults also are at high risk.
According to CDC data, approximately half of all of meningococcal infections occur in individuals between 15 and 24 years. “Studies have shown the case fatality rate to be especially high in this age group, but they have also shown the percent preventable to be very high,” said Dr. Marchant.