question and answer
Anatomy of a flu vaccine
December 2005
KIRBY SIMPSON, MD, of Vancouver, BC, wonders, "With the widespread circulation of the influenza A/Fujian strain in early winter 2004, it would have been advisable to have had it in the 2003-04 vaccine. Why are only three strains of influenza included in the annual flu vaccine? Would it be possible to vaccinate against at least seven or eight strains each fall?"
The yearly influenza vaccine is formulated to contain antigenic components most likely to afford protection against the current and emerging strains, based on national and international surveillance. The vaccine for 2005-2006, i.e. this year's, is recommended to include an A/New Caledonia/20/99-(H1N1)-like virus, an A/California/ 7/2004-(H3N2)-like virus and a B/ Shanghai/361/2002-like virus. For production purposes, vaccine producers may not necessarily use the actual strains but ones that are antigenically equivalent -- for instance, the marketed vaccines this year will contain A/New York/55/ 2004 for A/California/7/2004-(H3N2)- like virus, and B/Jiangsu/10/2003 in lieu of B/Shanghai/361/2002-like virus.

Early in the 2004-05 season, the predominant strains were A/Fujian/411/2002 (H3N2)-like (covered by A/Wyoming/3/2003-(H3N2) antigens included in last year's vaccine) and later on, they were A/California/7/2004-like (included in this year's vaccine).

The number of antigens included in the vaccine is selected based on a practical balance of issues like production considerations, costs and likely benefits. KL
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