This Week in Influenza


Almost 46% of the pediatric patients hospitalized with influenza during the 2010-2011 flu season so far and 17% of the hospitalized adult patients had no known underlying medical conditions, according to data reported by the Centers for Disease Control and Prevention.

Among pediatric hospitalized patients, the most common underlying conditions were asthma (seen in 20.6% of cases), cardiovascular disease, (6.1%), metabolic disorder (6.1%), neurologic disease (4.6%), and immune suppression (3.8%). Among adult hospitalized patients metabolic disorder was the most common underlying condition (seen in 32.2% of patients) followed by cardiovascular disease (27.8%), asthma (20.3%), chronic lung disease (18.6%), immune suppression (16.5%), and renal disease (16.5%).

In other influenza news:

• During the third week of 2011, 25 states reported widespread influenza outbreaks and another 16 reported regional outbreaks to the CDC. Four states and the District of Columbia reported local outbreaks. Another four states plus Puerto Rico and the U.S. Virgin Islands reported sporadic outbreaks. Of all the states and territories, only Guam reported that it had no influenza activity. (California did not report its influenza activity during this period.)

• In a study published Jan. 31 in PLoS ONE, a team of researchers from the Food and Drug Administration demonstrated that during the 2009-2010 influenza season, the trivalent seasonal flu vaccine provided a moderate amount of protection against 2009 pandemic influenza A(H1N1). As judged by hemagglutination inhibition assays (HAI), 24% of adults and 36% of elderly subjects who received only the seasonal flu vaccine achieved a seroprotective HAI titer against one of the main strains of pandemic influenza A(H1N1), compared with 4% and 7%, respectively, before vaccination. "A moderate boost on cross-reactive response to a novel influenza virus by seasonal vaccination may not lead to a complete protection against a pandemic, but might reduce the burden of infections substantially in affected subjects," the investigators wrote. "Ours and others’ studies suggest that annual seasonal vaccination plays an important role in protecting the public not only against seasonal flu but also a pandemic"(PLoS ONE 2011;6:e16650 [doi:10.1371/journal.pone.0016650]).

• A study of an H1N1 pandemic that began in an elementary school in April and May of 2009 and spread to a semirural community in Pennsylvania allowed investigators to quantify the role that social networks play in the spread of respiratory disease. The investigators – from Imperial College London, the CDC, and the Pennsylvania Department of Health – determined that sitting next to or being a playmate of a child who developed influenza did not increase the risk of transmission. However, the division of children into classes and grades did significantly affect the spread of the virus. Boys were more likely to spread the virus to other boys, and girls were more likely to spread the virus to other girls. The study was published online Jan. 31 (Proc. Natl. Acad. Sci. 2011 [doi:10.1073/pnas.1008895108]).

• According to reports by Russia’s Itar-Tass news agency, authorities have closed more than 1,500 public and private schools serving grades 1-8 in Moscow for a full week beginning Jan. 31 because of a widespread influenza outbreak. During the last week in January, about 91,000 individuals in Russia’s capital were on sick leave from influenza and other respiratory illnesses, with children making up more than 50% of that number.