Formulating the flu vaccine

Americans are still getting their flu shots for the 2008-2009 flu season, but the data-gathering is already well under way for formulating the flu vaccine that’ll be used a year from now.

Three strains of the influenza virus – two "A" viruses and one "B" virus – are included in each year’s version of the vaccine.

The selection process is a lengthy one that starts months in advance, as the U.S. Centers for Disease Control and Prevention describes:

The viruses used in making flu vaccine are chosen each year based on information gathered over the previous year about the strains of the flu viruses that are infecting humans and how they are changing. Circulating influenza strains and information on disease trends are gathered by 122 national influenza centers in 94 countries and the viruses and other data are further tested and combined data are analyzed by the four World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza located at the Centers for Disease Control and Prevention (CDC) in Atlanta; London, United Kingdom; Melbourne, Australia; and Tokyo, Japan. Based on this information, experts forecast which viruses are likely to circulate the following season and WHO recommends specific virus strains that can be used to make vaccines to protect against them.

Individual nations use this information to decide which strains to include in the flu vaccine for their country. In the United States, this decision is made each February by an advisory committee to the Food and Drug Administration.

This is the go-ahead for manufacturers to start producing vaccine for the next flu season. Some, in fact, start as early as January, using their best guess as to which flu strains are likely to be included in the vaccine.

In spite of the surveillance and data collection that are invested in determining the make-up of the flu vaccine each year, to some extent it’s guesswork – and it’s made more complicated by the flu virus’s tendency to "drift," or undergo mutation.

When the forecast turns out to be inaccurate, we have a flu season like last year, during which the vaccine was only a partial match to the predominant flu viruses. Many people got sick, in spite of being vaccinated.

Does this mean the flu shot is mostly a gamble and there’s no point in getting one? Not at all, says the CDC:

… antibodies created through vaccination with one strain of influenza viruses will often offer protection against, different, but related strains of influenza viruses. So even though circulating influenza viruses may "drift" or change from the time the vaccine composition is recommended, the vaccine can cross-protect against circulating viruses. The mismatch may result in reduced effectiveness against the variant viruses, but it still can provide enough protection to lessen illness severity.

This year’s flu shot is a new formulation that includes A/Brisbane/59/2007 (H1N1), A/Brisbane/10/2007 (H3N2) and B/Florida/4/2006.

There’s still time to get a flu shot – but hurry up, because the local vaccine supply won’t last forever.

Affiliated Community Medical Centers has run out of FluMist, the inhaled form of the vaccine. Shots are still available, however, and are being offered to patients on a walk-in basis.

Stacey Zondervan, director of patient services at Family Practice Medical Center, said the clinic has about 100 doses of flu vaccine left and will likely run out before Christmas. "Anyone that needs to have a shot should think about getting it fairly soon," she said.


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