Immunization Issues

Trivalent inactivated influenza vaccine (TIV) has been recommended for many years for children with underlying medical conditions and for children living in households with someone at increased risk of complications of influenza. More recently, TIV was first encouraged and then recommended for all children 6-23 months of age.

Many consider influenza as an illness of the elderly—because more people older than 65 years die every year of influenza than other age groups. However, various studies in the United States and Europe have shown that the highest rates of infection are among preschool and school age children.1

For instance, during regular influenza seasons as many as 30% of children may have influenza illness, and in day-care centers almost half of children may contract the disease.

In one study from Finland, the highest rate of culture proven influenza in children occurred in children less than 3 years of age. Acute otitis media was a complication of influenza in almost 40% of these children.2

Although influenza-related deaths are much less common in children than the elderly, fatal cases have been increasingly recognized.3

Children less than 2 years of age who contract influenza often appear quite ill and may have high fevers. Although there are rapid tests available to detect influenza viruses, influenza infection results in numerous hospital admissions, invasive diagnostic studies, and often antibiotic treatment until the specific diagnosis of influenza can be established or a serious bacterial infection can be excluded.1

Also, children can shed more virus and for a longer period of time in comparison with adults, probably making children the main disseminators of influenza in the community.

Influenza viruses change as people in the community become immune. As a consequence, often at least one of the three strains used to make the vaccine needs to be different each year. In 2001 some of the delay in having TIV available was because some of the manufacturers had difficulty preparing the new vaccine strain.

TIV is safe, effective, and potentially cost-saving in children.45 Its effectiveness will depend on how well matched the strains that were used to make the vaccine are with the viruses that are causing influenza illness in the community. In addition, other respiratory viruses that circulate during the winter months cause similar influenza-like illnesses in children; thus, TIV immunization will only prevent a portion of the respiratory disease seen each winter.6

For these reasons, the advisory groups have recommended that all children 6 to 23 months of age be vaccinated with TIV. TIV is not approved for use among children younger than 6 months of age, so the caregivers of children 0 to 5 months of age should be immunized to help protect these young infants.4

Vaccine supply

Prior to the shortage of TIV this year, influenza vaccination had been recommended for approximately 180 million people (78 million in high risk groups and another 102 million health care workers, household contacts and people 50 to 64 years of age).1 With the supply of TIV expected to be only about 60 million doses this year, the CDC has recommended that all available doses of TIV be directed to those at highest risk for complications of influenza, including young children 6-23 months of age and persons over 2 years of age with chronic medical conditions:

• Live in long-term care facilities
• Have long-term disorders of the lungs, heart, or circulation (including asthma or cystic fibrosis)
• Have metabolic diseases (including diabetes)
• Have kidney disorders
• Have blood disorders (including anemia or sickle cell disease)
• Have weakened immune systems (including immunosuppression caused by medications, malignancies, organ transplant, or HIV infection)
• Are children who receive long-term aspirin therapy
• Are women who will be pregnant during the influenza season (November to April)
• Are household contacts and out-of-home caregivers of infants younger than 6 months of age

Children less than 6 months of age are also at high risk of complications from influenza. Since influenza vaccine is not licensed for children less than 6 months of age, the only way to protect them is indirectly by trying to limit their exposure to the influenza virus through vaccination of their household contacts. For this strategy to be effective, influenza vaccine should be administered now to household contacts of infants expected to be delivered before the end of the influenza season.

In the past, it was recommended that all household contacts of all individuals at increased risk for complications of influenza receive TIV. However, because of the severe shortage of vaccine this year and because persons in the other risk groups can be immunized, close contacts of infants less than 6 months of age is the only group of contacts for whom influenza immunization is recommended.

Influenza vaccine for children

When children six months to nine years old of age are vaccinated against influenza for the first time, they should receive two doses of TIV given one month apart. For children 6-35 months of age, the amount that is injected is half (0.25 ml) of the usual dose (0.50 ml) given to everyone over three years of age.

Most of the available TIV is packaged in multiple dose vials containing the preservative thimerosal. Limited stocks of TIV are available packaged as 0.25 ml containing only trace amounts of thimerosal for children whose parents prefer that formulation.

In the United States, Fluzone® (Aventis Pasteur), the currently available TIV, may be administered to children as young as six months of age. However, Fluvirin® (Chiron Corp.)—the TIV that is not available this year—is not licensed for children less than four years of age. Any stocks of Fluvirin® should NOT be used as all new Fluvirin® has been embargoed and any remaining stocks from last year are out of date.

Live attenuated Influenza Vaccine (Flumist®) is an option for healthy individuals who are 5–49 years of age—particularly healthcare workers (except those who care for severely immunocompromised patients in special care units)—and who are not pregnant. Flumist® should not be administered to children younger than 5 years of age (or persons older than 49 years of age), pregnant women, or to persons with any underlying medical conditions.

Additional Reference

• Meltzer MI, Neuzil KM, Griffin MR and Fukuda K (2005). An economic analysis of annual influenza vaccination of children. Vaccine, 23(8):1004-1014.

References

• 1. a. b. c. Terebuh P, Uyeki T, and Fukuda K (2003). Impact of influenza on young children and the shaping of United States influenza vaccine policy. The Pediatric Infectious Disease Journal, 22(10):S231-S235.
• 2. Heikkinen T, Silvennoinen H, Peltola V et al. (2004). Burden of influenza in children in the community. Journal of Infectious Diseases, 190:1369-1373.
• 3. CDC. (2004) Update: Influenza-associated deaths reported among children aged <18 years-United States, 2003-04 influenza season. Morbidity and Mortality Weekly Report, 52(53), 1286-1288.
• 4. a. b. CDC. (2004). Prevention and control of influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 53 (RR-06), 1-40.
• 5. Ruben FL (2004). Inactivated Influenza Virus Vaccines in Children. Clinical Infectious Diseases, 38:678-688.
• 6. Neuzil KM (2004). Influenza Vaccine for Children. Clinical Infectious Diseases, 38:689-691.