Some progress reported on the flu front from 2010-2011 season, but work still to be done

CDC. MMWR. 2011;60(21);705-712.

The bulk of influenza-related morbidity and mortality has now shifted back to older people, but more than 100 influenza-related deaths were reported among children for the 2010-1011 influenza season, according to the latest CDC and WHO data.

Influenza activity for the 2010-2011 season peaked in early February and influenza A (H3N2) virus predominated. A total of 246,128 specimens were tested for influenza, of which 54,226 were positive (22%) and at least 311 deaths related to influenza, including 105 children, according to CDC and WHO.

Influenza A predominated

The report summarized the influenza season from Oct. 3 to May 21. Health officials reported that although influenza A (H3N2) remained the predominant virus throughout the season, the pandemic 2009 influenza A (H1N1) strain and influenza B viruses continued to circulate and dominate in certain areas.

“Of the 105 deaths, 40 were associated with influenza B viruses, 27 with 2009 influenza A (H1N1) virus, 18 with influenza A (H3N2) viruses, and 20 with influenza A virus for which the subtype was not determined,” the researchers wrote. They added that during the 2009-2010 pandemic, 348 pediatric deaths were reported between April 15, 2009, and Oct. 2, 2010. This was a significant increase from the 2008-2009 season, during which 67 influenza-associated pediatric deaths were reported, and the year before, when 88 deaths were reported.

Using FluSurv-NET surveillance data, health officials calculated the cumulative hospitalization rate (per 100,000 population) for this season and said the rate was “43.8 among children aged 0-4 years, 8.5 among children aged 5-17 years, 10.7 among adults aged 18-49 years, 21.7 among adults aged 50-64 years, and 62.5 among adults aged 65 years and older,” which was similar to rates in 2007-2008.

According to the Morbidity and Mortality Weekly Report, there were five cases of human infection with swine-origin influenza A (H3N2) viruses, three of which occurred in children. Two cases occurred in September in Pennsylvania and Wisconsin, one case in October in Pennsylvania, and two cases in November in Minnesota, according to health officials, who added that most of these patients had either direct or indirect contact with swine.

Next year’s vaccine

The researchers said the FDA’s Vaccines and Related Biological Products Advisory Committee has recommended keeping the same three influenza strains in the 2011-2012 influenza vaccine that are in the current season’s vaccine, which are A/California/7/2009 (H1N1)-like virus, A/Perth/16/2009 (H3N2)-like virus, and the B/Brisbane/60/2008-like virus.

Summarizing their report, the health officials wrote, “In comparison with the past three seasons, the 2010-2011 influenza season was less severe than the pandemic year and the 2007-08 season, but more severe than the 2008-09 influenza season, as determined by the percentage of deaths resulting from pneumonia or influenza, the number of influenza-associated pediatric deaths reported, and the percentage of visits to outpatient clinics for influenza-like illness.”

Kathryn M. Edwards

The CDC, in a recent MMWR, summarized the morbidity and mortality from the last influenza season, 2010-2011. The CDC data are enormously important as we seek to understand the impact of the influenza and its prevention. As with each year, many children are infected, many seek outpatient care, some are hospitalized, and a few die from influenza. The magnitude of the burden varies with the season, with previous experience of the population with the circulating strains, with the match between the vaccine strains and the circulating virus, and the percentage of the population that is immunized. Overall, last season was not as severe as the pandemic season and 2007-2008, but more severe than 2008-2009. What lies ahead for this upcoming influenza season is impossible to predict. The strains in the influenza vaccine will remain the same next year as they were this past year. That will mean that children immunized last season will only need one dose of vaccine this year. Vaccination rates in children still remain much lower than the universal recommendations for all children to be immunized, so we all have work to do to make certain more children are immunized. The most important factor in whether a child is immunized, is whether their health care provider recommends the vaccination. To reduce the influenza burden, we all need to recommend influenza vaccine and make sure that it is administered.

Kathryn M. Edwards, MD
Infectious Diseases in Children Editorial Board member

Disclosure: Dr. Edwards reports no relevant financial disclosures.

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