Falguni Shah, M.D.,
Pediatric Infectious Disease Consultant,
Saint Barnabas Medical Center
The control of infectious diseases through immunizations is hailed as one of the greatest medical advances. This is evident by the dramatic decrease in the number of vaccine-preventable diseases, the number of averted deaths, and the overall increase in health throughout the world. The global eradication of small pox in 1977 and the elimination of poliomyelitis from the Americas in 1991 serve as models for fulfilling the promise of disease control through immunization. High immunization rates have curtailed dramatically or almost eliminated diphtheria, measles, polio, rubella tetanus and Haemophilus influenza type B disease in the United States.
Yet, because organisms that cause these diseases to persist in the U.S. and around the world, continued immunization efforts must be maintained. Discoveries in molecular biology, immunology and medical genetics have resulted in burgeoning vaccine research. Licensing of new and safer vaccines, anticipated arrival of additional combination vaccines, and application of novel vaccine delivery systems, promise a new era of preventive medicine. The vaccines that have most recently been introduced for routine immunization schedules are: PCV7 (Pneumococcal conjugate vaccine), and the MCV4 (Meningococcal conjugate vaccine), and the combo vaccine, Tdap, for Tetanus Diphtheria and Pertussis.
Pneumococcal disease
PCV7 (Pneumococcal conjugate vaccine), which includes 7 of the 90 known pneumococcal serotypes, was recommended for use in infants in the U.S. beginning in 2000. Before introduction of PCV7, Streptococcus Pneumoniae was a leading cause of infectious morbidity in young children, causing sinusitis, otitis media, bacteremia, pneumonia, and meningitis. Active surveillance-based data show that within two years of PCV7 licensure, the rate of invasive pneumococcal disease in children younger than 2 years old declined by 69 percent. In addition, PCV7 may have an impact on reducing pediatric antibiotic prescription. PCV7 is recommended for infants at 2, 4, 6 months, with a booster at 12-18 months.
Meningococcal disease
From 2000 to 2002, approximately 2,400 to 3,000 cases of invasive meningococcal disease (meningitis, blood infection and pneumonia) occurred annually in the U.S. The fatality ratio for meningococcal disease is approximately 10 percent, and neurological disability and/or limb loss occur in approximately 10 percent of survivors. Approximately 5-10 percent of the U.S. population carries the meningococcal disease in their nasal passages. Transmission occurs through direct contact with respiratory tract droplets of infected individuals. The disease, while relatively rare, commands attention because it tends to occur in infants, adolescents and young adults entering college.
The newly licensed vaccine MCV4 (tetravalent meningococcal conjugate vaccine) promises to offer longer lasting immunity (approximately 8 years) because it elicits a T-cell dependent immune response. By preventing transmission from person to person, the vaccine will confer some degree of immunity to the general population. The new vaccine is expected to drastically reduce the prevalence of invasive meningococcal disease caused by Neisseria Meningitidis serogroups A, C, Y, and W-135, which make up the majority of cases in the US.
In Feb. 2005, the Advisory Committee on Immunization Practices for Meningitis and Pneumonia (ACIP) voted to recommend vaccination with MCV4 in the following groups:
Adolescents:
- Young adolescents at the pre-adolescent
visit (11-12 years old)
- Adolescents (if not previously vaccinated) at
high school entry (~15 years old)
- Adolescents who wish to decrease their risk
may elect to receive
Some of the groups that have elevated risk of Meningococcal disease:
- College freshman living in dormitories
- Military recruits
- Persons who travel to, or reside in, countries in which this disease is epidemic
Pertussis (whooping cough)
Pertussis remains endemic in the U.S. despite high immunization coverage rates of infants and young children. Immunity to pertussis wanes approximately 5-10 years after vaccination and loss of immunity seems to play a major role in the continued circulation of pertussis. How much of the reported increase in the incidence of this disease is due to enhanced surveillance or improved diagnostics is unclear. The burden of pertussis disease in adolescents is substantial.
After reviewing several strategies for pertussis vaccination in adolescents and adults, on June 30th, 2005, ACIP voted to recommend the routine use of Tdap vaccines in adolescents age11-18 in place of Td vaccines. The FDA recently licensed two Tdap vaccines for adolescents in the U.S. BOOSTRIX is licensed for use in adolescents 10 through 18 years of age, and ADACEL for persons 11 through 64 years of age. The committee is still reviewing the data for need and safety of adult immunization with above vaccine.
Rotavirus Gastroenteritis
Rotavirus is a common cause of gastrointestinal illness in young children. By five years of age, nearly all children test seropositive for rotavirus, indicating previous infection The first rotavirus vaccine, licensed in the U.S. in 1998, was removed from the market and from the immunization schedule in 1999. Currently several other rotavirus vaccines are in different stages of development.
Influenza
The threat of an unpredictable influenza pandemic and the concern about avian influenza heighten the importance of preventing morbidity and mortality caused by epidemics of influenza disease. Two types of influenza vaccines are licensed for use in the U.S. One is an inactivated vaccine recommended for persons >/= 6 months of age in high risk groups and their close contacts. The second is a cold adapted, live, nasally administered vaccine licensed for healthy people 5 to 49 years of age, including close contacts of high risk groups. The ACIP and AAP recommended in 2004 to expand influenza vaccine recommendation to include all children 6 to 23 months old and their household contacts, in addition to the children in the high risk group. Children 6 months to 8 years old are recommended to have 2 doses of vaccine administered 1 month apart if they have never been vaccinated.
To plan for the 2005-2006 influenza season, CDC encourages the following group of children to be prioritized to receive flu vaccines:
- All children age 6-23 months
- Children aged 6 months to 18 years on chronic aspirin therapy
- All children with chronic medical conditions.
Still to Come
The science behind new vaccines continues to advance at a remarkable pace, driven by an evolving understanding of the cellular and molecular processes involved in different responses of the immune system. Several vaccine combinations like MMRV (MMR + varicella), Hexavalent combo (DTap, Hib, IPV, Hep B), and a combo including DTaP, Hib, and polio are under phase II and phase III trails. Vaccines against the Human Papilloma virus HPV, the most common cause of sexually transmitted disease in men and women worldwide, causing almost all of the morbidity and mortality associated with cervical cancer, are in their final stages of phase III testing. A simplified single dose oral vaccine against Salmonella Typhoid (Typhoid fever), M01ZH09, is undergoing field studies.
As the recommended childhood and adolescent immunization schedule continues to expand, the U.S. immunization program will be challenged to integrate novel immunization strategies into the current immunization infrastructure. Despite the challenges, immunizations will likely remain on the list of great public health accomplishments of the 21st century. [ Back to Newsletter Index ]
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