US seeing flu strain not matched by vaccine

Feb 6, 2008 (CIDRAP News) – As seasonal influenza makes its annual march across the country, surveillance data from the US Centers for Disease Control and Prevention (CDC) reveals that 23% of the viruses that have been identified belong to a strain that is not included in this season's vaccine.

CDC Director Dr Julie Gerberding said the influenza A H3N2/Brisbane-like strain emerged at the end of Australia's influenza season, too late for inclusion in US flu vaccines, according to a Feb 2 report from the Associated Press (AP).

According to the CDC's most recent weekly flu report (for Jan 20 through 26), US laboratories have characterized 197 flu viruses so far this season. Forty-six (23%) were A/Brisbane/10/2007-like, which the CDC says is a recent antigenic variant that evolved from an A/Wisconsin/67/2005-like strain, a component of this year's seasonal flu vaccine.

The Brisbane-like viruses made up 87% of the 53 type A H3N2 isolates collected so far, according to the CDC. Of the other isolates, 101 were type A H1N1 viruses and 43 were type B viruses.

According to an influenza update from Canada that covers the same week, Canadian laboratories have analyzed 243 influenza samples so far this season and found that 12 (5%) were the Brisbane-like strain.

The World Health Organization (WHO) has said the Brisbane-like strain will be included in the southern hemisphere's 2008 seasonal flu vaccine.

This year's vaccine is still a good match for the strains responsible for most of the flu cases and should provide cross-protection against the new strain, Gerberding told the AP. "If people haven't gotten their flu shot, it really is still not too late," she said.

According to the CDC, 11 states are reporting widespread influenza activity and 26 are reporting regional activity.

In other seasonal flu developments, the CDC recently issued a health advisory to clinicians asking them to report all flu-related pediatric deaths and to have a high index of suspicion for coinfections, especially with methicillin-resistant Staphylococcus aureus (MRSA).

The CDC said the number of flu-related pediatric deaths during the 2006-07 season was moderately higher than in the previous two flu seasons. Of 73 pediatric deaths from influenza, 30 involved bacterial coinfections. Twenty-two of the patients were infected with S aureus. Of that group, 15 had MRSA infections.

According to the CDC's most recent update, only two influenza-related pediatric deaths have been reported this year. However, two states—Mississippi and New York—recently reported a total of four pediatric flu-linked deaths. The Mississippi State Department of Health reported on Feb 4 that two patients aged 18 or younger died of the illness. No other details about the patients were available, except that the deaths occurred in DeSoto and Madison counties.

Yesterday the New York State Health Department announced the flu-related deaths of two children, a 7-month-old from Monroe County and a 7-year-old from Orange County. The children were positive for influenza A and B, respectively, the department said. No other details were provided.

Richard F. Daines, MD, New York's health commissioner, in the statement urged parents to vaccinate their children against seasonal flu. "These tragic deaths underscore the serious threat seasonal influenza poses, particularly for the very young, the elderly, and anyone with a chronic medical condition," he said.

"Anyone who wants to reduce their risk of for flu should get vaccinated. It's not too late," he said.

See also:

WHO recommendations for the 2008 southern hemisphere flu vaccine

Feb 4 Mississippi State Department of Health press release

Feb 5 New York State Department of Health press release

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