Next year’s flu vaccine is getting a complete overhaul to provide protection against three new and different influenza strains for better protection than this year’s version.   Advisers to the Food and Drug Administration unanimously supported the change last week, echoing an earlier decision by the World Health Organization. It’s a highly unusual move: Seldom are more than one or two strains swapped out from one year to the next.  The question that remains is whether vaccine manufacturers can make such a big change in time to produce more than 100 million doses by the fall.   A strain called Brisbane/10 that’s responsible for much of this season’s flu grows very slowly in the laboratory, potentially complicating already laborious vaccine production.  The flu vaccine is reformulated every year to keep up with the fast-evolving influenza virus, and this year the CDC made a rare wrong bet on which strains would cause the most disease. The flu season got off to a slow start, but it rocketed in mid-January as some new strains arrived — and the CDC found the vaccine is a good match for only about 40 percent of the virus now spreading in the U.S.  That Brisbane/10 strain is the big culprit, one first spotted in Australia late last winter, too late for scientists to include in this year’s vaccine recipe even if they had predicted it would gain steam for reasons mentioned above.  Flu viruses come in different strains that constantly mutate, until one that few people have immunity against emerges and is able to spread widely. Each year’s vaccine contains protection against two varieties of the harsher Type A flu — subtypes known as H1N1 and H3N2 — and one from the more benign Type B family.

CDC and international authorities expect Brisbane/10, a version of the H3N2 flu, to still be lingering aroud next year. They predict a second new Type A strain, known as H1N1/Brisbane/59, also will hit, along with a newer Type B/Florida strain.  The recipe must be set about eight months before manufacturers start shipping doses because flu vaccine production is so complex. Health authorities come up with seed stocks of the virus strains that manufacturers then must grow in chicken eggs.  As for the rest of this winter, the CDC says the current vaccine should provide some protection, perhaps resulting in a milder case of flu than if someone hadn’t been inoculated. Every year, the flu infects up to 20 percent of the population, hospitalizes 200,000 people and kills 36,000.