Flu shot protects kids - even with a suboptimal vaccine match

Nov 3 2008

Children who receive all recommended flu vaccine doses are less likely to catch the respiratory virus that the CDC estimates hospitalizes 20,000 children under 5 years old every year.

This is according to new research published in Pediatrics by the University of Rochester Medical Center and colleagues from Vanderbilt University, Cincinnati Children's Hospital and the CDC. The study looked at children between 6 months (the youngest able to receive the vaccine) and 5 years old in 2003-2004 and 2004-2005. The study found that, even though those years had suboptimal matches between the vaccine and the circulating flu strains, the shots were clearly protective during the 2004-2005 year and possibly even during the 2003-2004 year.

"In these years, fully vaccinated children were about half as likely to get the flu," said Katherine Eisenberg, B.A., an M.D., Ph.D. candidate at the University of Rochester School of Medicine and Dentistry and author of the paper published this month. "We saw a reduction in both influenza-related hospitalizations or emergency room visits and influenza-related visits to doctors' offices."

The study, which was performed as part of the CDC-funded New Vaccine Surveillance Network, included 2,400 children from 6 months old to 5 years old in Rochester, Nashville and Cincinnati. Nasal and throat swabs were used to determine whether children who came to the hospital or participating outpatient practices had the flu.

In the 2004-2005 flu seasons, the vaccine was effective almost 60 percent of the time in children between 6 months and 5 years old who were fully vaccinated compared to those who were not. Partial vaccination (receiving one shot when two are recommended) did not provide any protection. This highlights the importance of having children receive full vaccination. Receiving only partial vaccination has not been shown to protect children from flu, Eisenberg said.

Only 6 percent of the children in the study were fully vaccinated in 2003-2004 and 19 percent were fully vaccinated in 2004-2005. The 2004-2005 season was the first year the CDC recommended children up to 5 receive the vaccine. The CDC now recommends children up to 18 years old receive the vaccine.

"It is incredibly important for all children to receive flu vaccinations and to make sure that people who live with or care for children under 5 years old also get vaccinated," said Peter Szilagyi, M.D., M.P.H., a professor of Pediatrics and Community and Preventive Medicine at the University of Rochester Medical Center and an author of the paper. "Since the vaccine is not 100 percent effective, it is very important to also vaccinate those who are close to children, especially those around children under 6 months of age. These youngest children are at the highest risk of influenza complications but they are too young to get vaccinated.Vaccinating those around them is the best way to protect our youngest children."