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CDC: flu vaccine has 38% failure rate this season

by Matt Rosenberg January 22nd, 2013

In little more than six out of ten instances – or 62 percent of the time – has flu vaccine actually prevented patients from getting the influenza virus, according to early results for this winter reported from sampling in five U.S. regions including Seattle. The news comes in a recently-released brief from the U.S. Flu Vaccination Effectiveness Network, that was published in the U.S. Centers For Disease Control open access journal Morbidity and Mortality Weekly Report. The good news for the Seattle area is that it had the highest “influenza-negative rate,” of 76 percent, among the five sampled regional health systems.

Network partners reporting were Group Health Cooperative in Seattle, and other medical centers in urban areas of Michigan, Texas, Pennsylvania, and Wisconsin. General prevalence of the flu right now is reported separately by the CDC as widespread in 48 states.

About the vaccine effectiveness sampling and rates, the new report’s authors from the five VE Network medical centers wrote, “these early estimates indicate some persons will become infected with influenza, despite having been vaccinated. Therefore, anti-viral medications should be used as recommended for treatment in patients regardless of their vaccination status” within 48 hours of apparent onset of flu. The Washington State Department of Health last week stressed that same point in a flu alert. A separate CDC page lists details on several anti-viral drugs often prescribed for flu.

The vaccine effectiveness review has been done by the so-called VE Network in the U.S. each flu season since 2004-05. For this preliminary assessment, researchers identified and surveyed 1,155 adults and children total at the five regional health systems who had come in from early December through early January for treatment of acute respiratory infection, which can include flu, common cold, strep throat or a respiratory virus.

Through a brief screening survey they ascertained that each of the patients to be included in the assessment had within the last two weeks gotten a flu vaccination. From each patient they collected respiratory specimens using throat or nose swabs and sent the specimens to the Network’s lab for analysis using CDC procedures to see which patients had Influenza A or Influenza B. The flu vaccine effectiveness rates were developed from the resulting analysis of the specimens from the 1,155 subjects. Overall 36 percent of the subjects tested positive for Influenza A or B despite having had recent flu vaccination. After adjustment for factors in play at study sites, the 64 percent protection rate was revised to 62 percent.

The 62 percent level of protection afforded by the flu vaccine so far this season is best described as “moderate,” but that still brings important benefits such as reductions in illness, doctor vista, time lost from work, hospitalizations and deaths, according to the report. Data from last flu season collected by the CDC from January to March 2012 showed a 52 percent flu vaccine effectiveness rate but even a rate as low as 50 percent provides worthwhile protection, the CDC said then. In the 2010-2011 flu season the overall flu vaccine effectiveness rate in the U.S. was about 60 percent, according to another CDC web page. In a conference call with reporters last week about the new data, CDC officials found themselves at one stage pressed to defend this year’s preliminary rate of 62 percent, which some saw questioners saw as insufficient but which the CDC defended as providing “a substantial public health benefit.”

Further testing by the VE Network will be done through the end of this flu season and results updated. Meanwhile vaccine supplies are becoming depleted. By early January, 128 million of the 135 million flu vaccine doses expected to be available this season nationwide had already been used. The authors advise that “persons seeking vaccination might need to call more than one provider” to get a dose administered. You can use the flu vaccine finder from Health Map, searching by zip code. There are more than 41,000 providers nationwide.


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