Novel H1N1 flu activity continues at unusual levels

Jul 24, 2009 (CIDRAP News) – Pandemic H1N1 influenza activity decreased for the fourth consecutive week, though the percentage of deaths from pneumonia and influenza rose a bit above the epidemic threshold, the US Centers for Disease Control and Prevention (CDC) said today.

The nation's number of lab-confirmed novel flu cases rose to 43,771, including 302 deaths, the CDC said. Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, said at a press conference today that this would be the last national case count update, though the CDC will still provide regular updates on hospitalizations and deaths.

Many public health officials say keeping case counts in countries that have had ongoing widespread transmission isn't useful, because it dramatically underestimates the true burden of the disease and can be a waste of public health resources.

On Jul 16 the World Health Organization (WHO) announced it would no longer provide a regular global case count, but would instead issue periodic surveillance updates and will still issue case counts for areas in which the virus is just beginning to circulate.

Unusual activity for summer
In a statement today, the WHO said the number of pandemic H1N1 cases is still increasing substantially in many countries, even in those that were first affected. Most countries are reporting that most cases continue to occur in younger people, with a median age of 12 to 17 based on information from Canada, Chile, Japan, the United Kingdom, and the United States.

Despite the dip in lab-confirmed cases in the United States, Schuchat said the level of flu circulation is still very unusual for the summer months. She added that the CDC has gotten reports of outbreaks at summer camps and military academies where people from different parts of the country come together. "Unfortunately, it's been a challenging summer," she said.

Seven states are reporting widespread activity, including California, Delaware, Georgia, Hawaii, Maine, Maryland, and New Jersey, the CDC said in its flu surveillance report for the week ending Jul 17. Thirteen states and Puerto Rico are experiencing regional activity. Many of the states reporting regional activity are on the East coast.

Five pediatric flu deaths were reported during the past flu surveillance week, though some occurred as far back as February. Four of the deaths were from novel H1N1, and one was associated with an influenza B virus. Of the 95 pediatric deaths that have been reported during the current flu season, 27 were related to the new flu virus.

More than 99% of all subtyped influenza A viruses reported to the CDC were the novel flu strain.

Pneumonia and influenza deaths, tracked through the 122-Cities Mortality Reporting System, were at 6.7%, which is slightly above the 6.5% baseline.

Seasonal flu vaccine recommendations
In other developments, the CDC today issued its recommendation for the seasonal flu vaccine, which appeared in an early edition of Morbidity and Mortality Weekly Report (MMWR). For the first time, the CDC recommends, rather than encourages when feasible, the shot for children aged 6 months to 18 years. Today's appeal is part of a gradual phase-in of the Advisory Committee for Immunization Practices (ACIP) recommendation for kids, Schuchat said.

The CDC now recommends the seasonal flu vaccine for about 83% of the population or for anyone who wants to reduce their risk, she said. However, only 40% of the recommended groups received their flu vaccine last year, she added.

The 2009-10 vaccine contains a different influenza B strain from last year's version but the same seasonal H1N1 and H3N2 strains.

Seasonal flu vaccine immunization campaigns should begin as soon as the vaccine is available to make way for another possible round of vaccination against the pandemic H1N1 virus, she said.

See also:

CDC weekly flu surveillance report

Jul 24 WHO statement

Jul 24 MMWR report

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