Even in an influenza season where there is not an optimal match between circulating strains of influenza and the strains contained in the influenza vaccine, the vaccine is likely to significantly protect young children, aged six months to five years, against influenza, new research indicates.
Influenza vaccine effectiveness has not been well characterised in this age group and can vary from season to season, the research team notes in the November issue of Paediatrics.
To investigate, Katherine W. Eisenberg from the University of Rochester, New York, and colleagues conducted a study of children treated for an acute respiratory infection during the 2003-2004 and 2004-2005 influenza seasons. The 288 children with laboratory-confirmed influenza were the cases; and the 744 children who tested negative served as controls.
“There was an almost 60 per cent reduction in influenza-related medical visits among 6- to 59-month-old children who received all recommended doses of the influenza vaccine compared to unvaccinated children in one of the two influenza seasons we studied (2004-2005),” Dr Eisenberg, currently in year six of an MD/PhD programme at the University of Rochester.
In the 2003-2004 season, there was a 44-per cent reduction in influenza-related medical visits, which is “consistent with vaccine effectiveness that year, although this finding was not statistically significant,” Dr Eisenberg noted.
In the 2003-2004 season, she explained, relatively few children were vaccinated because the formal recommendation for vaccination of healthy children in this age group was not in place until the following year. “This limited our ability to detect the effectiveness of the vaccine,” Dr Eisenberg said.
“We did not find any protection against flu for children who needed two vaccine doses and only received one,” she also noted.
These findings on influenza vaccine effectiveness in this age group are important, the researcher said, “because the match between the influenza strains in the flu vaccine and the strains circulating in the community was suboptimal in the years we studied, and we still found that the vaccine was 57-per cent effective at preventing influenza-related medical visits in our study population in one of the two seasons. In a year with a better match, the potential for a reduction of illness is even greater.”
The message for parents, Dr Eisenberg added, is that “it is important to have young children vaccinated against the flu, even in a year when the vaccine and circulating flu strains may not match perfectly.”
“Children six months up to 9 years of age need to have two vaccine doses if they are getting a flu vaccine for the first time,” she stressed, “Otherwise they may have reduced or no protection against the flu.”
Reuters Health
Source: Paediatrics, November 2008.