Flu Activity Called the Lowest in 4 Years

23 March (icanNEWS)—Influenza activity in the United States peaked at the end of January, and activity has remained moderate and lower than the previous 3 seasons, according to a report in the 23 March Morbidity and Mortality Weekly Report [1]. The predominant influenza strain circulating this year, influenza A (H1N1), last circulated widely in the United States during the 1995–96 and 1988–89 seasons. Influenza A (H1N1) viruses circulated from 1918 to 1957, then didn't reappear until 1977. “Since their reappearance in 1977, influenza A (H1N1) viruses have had less impact on persons born during or before the mid-1950s than on those born after that time, probably because immunity developed during the 1940s and 1950s,” the report says. The percentage of pneumonia and influenza deaths has remained below the epidemic threshold throughout the season so far. During the previous 3 seasons, the percentage of deaths attributed to pneumonia and influenza was above the epidemic threshold for 10 consecutive weeks each season. Patient visits to sentinel physicians for influenza-like illness peaked at 4.1% during the week ending 27 January, the report says. Although the predominant influenza strain circulating this season has been influenza A (H1N1), the proportion of influenza B virus isolates has been increasing. During the weeks ending 24 February, 3 March, and 10 March, 70% of isolates nationwide were influenza B.