US flu update shows continuing slow increase
The United States saw another small uptick in flu activity last week, with increases seen in most indicators that the US Centers for Disease Control and Prevention (CDC) uses to track the season. The percentage of respiratory specimens that tested positive for flu climbed from 4.2% to 5%, with the percentage of clinic visits for flulike illness hovering just above the national baseline.
The 2009 H1N1 virus remained the dominant strain, and the cumulative hospitalization rate rose a bit to 2.1 per 100,000 population. No pediatric flu deaths were reported last week, keeping the season's total at seven for the season. Overall deaths from pneumonia and flu were close to seasonal baselines in the two surveillance systems CDC uses to track that indicator.
Puerto Rico was the only area to report high flulike illness activity, another measure of clinic visits. Four states reported widespread geographic spread of flu, up from three the week before. They include California, Maryland, Massachusetts, and North Carolina.
Jan 29 CDC FluView report
Australia sorts out rare influenza B dominant flu season
Virologists in Australia yesterday reported that the country's 2015 flu season was marked by the predominance of influenza B, an event it sees about once a decade. Their report in Eurosurveillance also noted that the influenza B lineage switched from the Yamagata lineage to the Victoria one, which came with differences in affected age groups.
The team noted that Europe's last flu B dominant season was 2005-06, with the United States last seeing the strain as the highest proportion during 2002-03.
The Southern Hemisphere's flu vaccine last year targeted the Yamagata lineage of influenza B, and as the dominant lineages waxed and waned, the Victoria lineage seemed to affect a greater number of younger age groups, with age-group distribution more even for the Yamagata lineage, in line with an earlier household study from Hong Kong. Possible explanations could include different responses among kids to influenza B antigens or age-related differences in receptor specificity to the different lineages, or perhaps a combination of both, the authors wrote.
They added that the Victoria lineage is likely to increase during the Northern Hemisphere's flu season, where the trivalent vaccine targets the Yamagata strain, and that use of quadrivalent vaccine might improve vaccine effectiveness.
Jan 28 Eurosurveill report