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Influenza vaccine benefits extend beyond sick children to families
Children play an important role in the epidemiology of influenza, making vaccination essential in this population.
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Children have high rates of influenza and influenza-related complications, antibiotic use and health care visits, making influenza vaccination in this population key, according to Janet A. Englund, MD.
“Children are important vectors in the spread of influenza,” Englund, associate professor of pediatric infectious disease, allergy and rheumatology at the Children’s Hospital and Regional Medical Center, University of Washington, told Infectious Diseases in Children. “This is because they are not as experienced in having had influenza before, so they shed higher amounts of virus for longer periods of time.”
Young children are typically in close contact with one another and congregate in large groups, such as at school or in day care, where viruses can easily be transmitted from person to person when hand hygiene practices may not be at their best.
Children aged younger than 1 year tend to have the highest number of influenza-attributable outpatient events, as well as the highest number of hospitalizations attributed to influenza.
Furthermore, these children are cared for by adults, who have close contact with the child’s contagious secretions and can easily be infected as well, according to Englund. In this way, children are often responsible for the start of an epidemic.
“Children come first. They get sick, they have high rates of admission and they spread the disease,” she said during a presentation at the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy, held in Chicago.
Englund’s presentation focused on the use of influenza vaccine in this population, as well as on the effects that immunizing children can have on their communities.
Vaccine dosing in toddlers
“It has been established and it is still the case that toddlers do need two doses of flu vaccine,” said Englund, who is also an affiliate investigator for the division of clinical research at the Fred Hutchinson Research Center, Seattle.
In a study conducted by Englund and colleagues, data showed that participants (n=122; age range, 6-23 months) who received two doses of influenza vaccine had higher percentages of protective antibody levels than participants who received only one dose.
Results from a retrospective study in Colorado demonstrated that in the 6- to 23-month-old cohort (n=29,726), two doses of vaccine resulted in 23% protection against influenza-like illness and 51% protection against both pneumonia and influenza-like illness, according to Englund.
However, getting this second dose to children has proven problematic.
Results from the Vaccine Safety Datalink study showed that among 125,928 children aged younger than 9 years, 50% or less had received their second dose of flu vaccine.
“It varies by year between 2001, 2002 and 2004, but basically we as a community are not doing well giving them that second dose of flu vaccine,” Englund said. “We are not doing that well with the 2- to 8-year-olds, either. In fact, we are doing worse.”
Herd immunity effect
“Should herd immunity be a basis for influenza vaccine recommendations? It certainly should be part of the consideration,” Englund said. “Day care centers, however, are not pivotal in the spread of influenza, especially compared with school-aged children.”
Although the idea of herd immunity may not be the strongest argument to support the need for vaccination in potentially healthy individuals, parents should still be encouraged to vaccinate their children because they themselves may benefit, according to Englund.
In a study by Piedra et al, researchers administered a single dose of cold-adapted influenza vaccine trivalent (FluMist, MedImmune) to 4,298; 5,351; and 5,150 age-eligible children at intervention sites during three consecutive influenza vaccination seasons. These children represented between 20% and 25% of all age-eligible children from that area.
Age-specific medically attended acute respiratory illness rates for the vaccinated children were then compared with those of participants from comparison sites.
According to the researchers, during the subsequent three influenza seasons, comparison participants in the 35 to 44 years, 45 to 54 years, 55 to 65 years and 65 years and older age groups experienced reductions in medically attended acute respiratory illness rates.
In particular, adults aged 35 years and older experienced reductions of between 0.08 and 0.18 in acute respiratory illness-related doctor visits per year.
“That is an indirect protection of 8% to 18%, and that was only [after] vaccinating 20% to 25% of the children,” Englund said.
Englund discussed another study in which students from 28 schools in four states were randomly assigned to either receive vaccination with live-attenuated influenza vaccine or to be in a control group without vaccination; 47% of students in the intervention schools received the vaccine.
“Among children and adults in target households — that is, in households where the child in school received the vaccine — there were fewer episodes of influenza-like illness, fewer visits to the doctor, less frequent use of over-the-counter medications [and] less frequent use of prescription medications,” Englund said.
In light of these results, it is possible that vaccinating school children can help prevent disease in other people as well, according to Englund.
The community cannot rely solely on the vaccination of school aged children to prevent the spread of infection within the community. Conversely, immunizing the community could play a large part in preventing infection in day care centers, she said.
“I would like to say that day cares are safer now with the widespread use of influenza vaccine in young children,” Englund said. “It would be even safer with increased use of influenza vaccine in children and family members of all ages.” – by Cara Dickinson
For more information:
- Englund JA. Are children attending day care safer in this era of vaccines: influenza. #1967. Presented at: the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy; Sept. 17-20, 2007; Chicago.
- King JC Jr, Stoddard JJ, Gaglani MJ, et al. Effectiveness of school-based influenza vaccination. N Engl J Med. 2006;355:2523-2532.
- Piedra PA, Gaglani MJ, Kozinetz CA, et al. Herd immunity in adults against influenza-related illnesses with the use of the trivalent-live attenuated influenza vaccine (CAIV-T) in children. Vaccine. 2005;23:1540-1548.