Thursday, December 14, 2006

Studies Support Flu Vaccine's Effectiveness

(HealthDay News) -- Two new studies provide encouraging news about the flu vaccine.
The first found that even when circulating strains of the virus don't perfectly match those included in that year's immunization, the vaccine still provides protection against flu.

The second study found that a school-based immunization program is an effective way to deliver the vaccine, and vaccinating children appears to protect other non-immunized family members against the flu as well.

"These findings are very reassuring and tell us that this vaccine is doing what we hoped it would be doing," said the senior author of the first study, Dr. Arnold S. Monto, a professor of epidemiology at the University of Michigan School of Public Health in Ann Arbor.

Both studies appear in the Dec. 14 issue of the New England Journal of Medicine.

Every year, as many as 20 percent of all Americans are infected with the influenza virus, according to the U.S. Centers for Disease Control and Prevention. Aside from the muscle aches, fever, headache and general misery that the flu is so well known for, the virus can also cause serious complications, including ear infections, pneumonia and dehydration. About 200,000 people are hospitalized each year due to flu complications, and as many as 36,000 die each year from this viral infection, reports the CDC.

There are numerous strains of the flu virus, and these strains are constantly changing. As a result, the vaccine changes annually. Each year, the seasonal flu vaccine includes what health experts expect will be the three top strains circulating that year. While often quite accurate, the vaccine doesn't always match the strains that end up circulating in any given season.

Estimates of the vaccine's efficacy are based largely on studies done with military personnel in years when the vaccine closely matched the flu going around that year. To better assess what happens on a community level, Monto and his colleagues began a three-year study in the 2004-2005 flu season. The current study includes data from the first year of the study.

That year, their study included 1,247 healthy adults who were vaccinated -- either with the live vaccine given nasally or the inactive vaccine which is given by injection -- between October 2004 and December 2004. If someone became ill anytime after receiving the vaccination until May 2005, they were given a throat swab so that the researchers could confirm influenza infection.

Even though the strains that circulated during the 2004-2005 flu season differed somewhat from the strains included in the vaccine, the inactive vaccine was still up to 77 percent effective, the researchers report, and the live vaccine was up to 57 percent effective in preventing flu.
"We've got two effective flu vaccines. In this particular year, the inactivated vaccine worked somewhat better than the live attenuated vaccine in adults," said Monto. He added that, in children, the live vaccine may prove to be more effective.

The second study compared children who participated in a school-based immunization program to kids from schools that did not. Children from 28 elementary schools in Maryland, Minnesota, Texas and Washington were included in the study. Eleven schools from that group were chosen as "intervention schools," and all healthy children over the age of five were offered the live nasal-spray vaccine. The remaining schools did not offer such programs and served as controls.

Using surveillance data, the researchers predicted what the peak week of influenza season would be. They also had parents answer questionnaires about what symptoms, if any, they and their children were experiencing, what medications they had purchased, and any doctor visits, missed school or work days they had logged.

The team found a significant reduction in influenza-like illnesses in both adults and children from households with a vaccinated child compared to the non-vaccinated households. The researchers also saw significantly fewer numbers of medical office visits, lowered use of prescription and over-the-counter medications and a reduction in missed school days by elementary and high-school children in the vaccinated households.

"Kids are the primary transmitters of flu to the community," explained the study's lead author, Dr. James King, a professor of pediatrics at the University of Maryland School of Medicine in Baltimore. "I think the influenza vaccine should be recommended for all children. Not only does the vaccine protect the children given the immunization but also the other family members."

He added that the school-based program was very effective and said that schools could be "a very viable adjunct" to vaccine distribution.

More information
To learn more about flu vaccine, visit the U.S. Centers for Disease Control and Prevention.

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