A look at the 2003-2004 flu season

FDA Consumer, March-April, 2004 by Michelle Meadows

Overall, the flu hit people in the United States earlier than usual during the 2003-2004 flu season, and lab tests showed evidence of a strain of the virus that's typically associated with more severe seasons. Taking a cue from the flu season just ending, experts say it's not too early to make a note for this fall: Vaccination is the best protection against the flu and can prevent many illnesses and deaths. Even for people who come down with the flu after vaccination, the illness is generally less severe than in people who didn't get vaccinated.

A Serious Illness

Media reports in November 2003 highlighted flu-related deaths in children in Colorado. But experts stress that flu, a contagious respiratory illness caused by the influenza virus, is serious every year. "Influenza is always the most important cause of acute respiratory illness that causes patients to seek medical care each year," says Paul Glezen, M.D., a professor of molecular virology and microbiology at Baylor College of Medicine in Houston. "Children are bit hard each year. This is a particularly bad epidemic, and we have had several deaths here in Texas, though not the same publicity as with Colorado."

Between October 2003 and early January 2004, the deaths of 93 children younger than 18 had been reported to the Centers for Disease Control and Prevention (CDC), according to preliminary data. Of the 45 children with a known vaccination status, one child had received adequate vaccination, 33 were not vaccinated, five were reported as vaccinated but the interval between vaccination and onset of illness had not been documented, and six children had received one dose of vaccine. It is recommended that children younger than 9 who haven't been previously vaccinated receive two doses of the flu vaccine about one month apart.

In addition to deaths, many more children have been hospitalized. Glezen says, "I think we need to take greater notice of the serious consequences of a vaccine-preventable disease like influenza."

Though it hasn't been in the news as much as the flu cases in children, older people also face a disproportionate number of hospitalizations and deaths due to flu every year. Millions of the people who get the flu--about 10 percent to 20 percent of Americans each year--recover in a week of two without complications. But about 36,000 people die each year from the flu and 114,000 per year are hospitalized, according to the CDC.

The main symptoms of the flu are headache, fatigue, body aches, cough, sore throat, and congestion. The illness can result in complications such as pneumonia, bronchitis, dehydration, and sinus and ear infections. People at high risk for flu complications include children ages 6 to 23 months, adults 65 and older, pregnant women in the second or third trimester during flu season, and people of all ages with underlying chronic conditions, such as heart disease and asthma or other lung diseases.

Supply and Production

Consumer demand for the flu vaccine increased considerably after reports in November 2003 of flu-related deaths in children. Manufacturers had produced about 87 million doses for the 2003-2004 flu season, including 4 million doses in the form of FluMist, a new nasal spray vaccine made by MedImmune Inc. of Gaithersburg, Md.

Because some states had excess supplies of flu vaccine, while other areas ran out, the CDC encouraged state health departments to coordinate with local health officials and other partners to redistribute vaccine among health care providers. The CDC purchased additional doses of flu vaccine from the two manufacturers of inactivated flu vaccine licensed in the United States: Aventis Pasteur of Swiftwater, Pa., and Evans Vaccines, a subsidiary of Chiron Corp. with manufacturing facilities located in Liverpool, England. Some people mistakenly thought that this was a special import of European vaccine, but Evans is a U.S.-licensed manufacturer of vaccines approved by the Food and Drug Administration. Both Aventis Pasteur and Evans prepared additional doses that they had not previously intended to market because demand for the vaccine appeared to have peaked in early to mid-November. The CDC also negotiated a contract for another 3 million doses of FluMist that state and local health departments could purchase as needed.

A new flu vaccine is required most years because the circulating flu viruses mutate frequently, producing new strains from year to year. Besides selecting suitable viruses, producing the flu vaccine involves growing the viruses in eggs and conducting tests to ensure safety and purity.

"Most of the surveillance data about the emergence of new influenza viruses are collected in January and February, and in most years, we've finalized [the selection of] strains by March," says Roland Levandowski, M.D., a virologist in the DKs Center for Biologics Evaluation and Research. "The vaccine has to be made by early summer to be ready for fall."

The three strains in the vaccine for 2003-2004 were called A/Panama, A/ New Caledonia, and B/Hong Kong. A new strain called A/Fujian was identified, but too late to include the virus in vaccine production. This year's predominant flu strains circulating turned out to be similar to the Fujian strain that wasn't included in the vaccine. Questions have been raised, and studies are still being done, about whether this year's flu vaccine was a good enough match to protect against the Fujian strain. But experts say that, even in years when the vaccine is not a good match, it usually provides some protection.