This winter’s flu season turned out to be only moderately severe despite an early start and a vaccine that didn’t include the influenza strain that caused most illness, according to government data presented Wednesday.
The World Health Organization is recommending that that strain, called Fujian, be included in next winter’s flu vaccine, because of early signs that it will again circle the globe.
A Food and Drug Administration committee is expected to decide Thursday whether to follow that recommendation. Complicating its decision is confusion over just how well this winter’s imperfect vaccine protected people. The committee saw conflicting research Wednesday that indicated a range of results, from no protection to a fair amount.
“It’s hard to make sense of it,” said Dr. Bruce Gellin, director of the government’s National Vaccine Program and a consultant to the FDA panel.
Flu viruses come in different strains that constantly mutate. Type A strains are always the harshest, particularly a type known as H3N2. Fujian is a new H3N2 strain.
Typical year for the flu
Despite fear that the new Fujian strain would make this winter’s flu season unusually harsh, and aside from beginning a month early, it turned out to be a pretty typical H3N2 year, said Ann Moen, an influenza specialist of the Centers for Disease Control and Prevention.
Flu and pneumonia accounted for 10 percent of all deaths during influenza’s peak in late December, she said. That’s just shy of the flu’s death toll in 1999, the last time an H3N2 strain predominated.
“This season wasn’t greater in magnitude in terms of mortality than previous H3N2 seasons,” Moen said.
There also was concern about whether this winter’s flu was particularly deadly to young children. The CDC so far knows of 134 flu-associated deaths among children, 82 of them in youngsters under 5, Moen said. In the 1990s, there was an average of 92 deaths a year among children under 5. Studies to determine if child hospitalizations increased this winter aren’t yet complete.
Vaccine no match for strain
The flu vaccine is reformulated every year to try to match the three strains — two Type A varieties and one more benign Type B variety — that specialists predict are most likely to strike. It has to be done months in advance so manufacturers have time to brew vaccine.
Last fall’s vaccine wasn’t as good a match as usual. That’s because the first signs that Fujian flu had formed and might become a threat didn’t appear until February 2003 — and manufacturers couldn’t reliably make anti-Fujian vaccine until June. So a year ago, the FDA committee crossed its fingers and ordered a close relative of the Fujian strain into the coming season’s vaccine, assuming it would offer some protection.
It is unclear just how much.
Preliminary results of a CDC study of 50- to 64-year-olds in Colorado, among the first states hard-hit by flu, found those at particularly high risk from influenza got little if any protection.
But a military study of the families of 114 Air Force personnel who caught the flu suggests the vaccine was 40 percent effective. And a study by France’s National Institute for Health and Medical Research suggests the vaccine was 60 percent effective. (France experienced a flu season almost identical to the United States’, and used the same vaccine.)
When the vaccine is a good match to circulating strains, it is 70 percent to 90 percent effective at protecting people from flu.
So what does this winter’s experience mean in preparing for coming rounds of flu?
Several FDA panelists wondered if manufacturers could have prepared a separate, Fujian-only shot to supplement last fall’s already-brewed vaccine — an option that might be available the next time the world is surprised by a new flu strain.
The nation tried that once before in 1986, but it wasn’t ready until late November, and doctors who had already given their patients regular vaccine didn’t know what to do with the new supplementary shot so most was wasted, said FDA’s Dr. Roland Levandowski.
If nothing else, this winter’s confusion shows the nation needs a better system of tracking how well each year’s flu vaccine works, Gellin said — information that’s important when determining the coming year’s recipe.