The article discusses influenza activity taking place in the U.S. during October 2 - November 26, 2011 as well as updates the earlier details. Influenza activity during the period remained low and ...the predominant viruses have been the influenza A ones.
CDC collects, compiles, and analyzes data on influenza activity year-round in the United States. The influenza season generally begins in the fall and continues through the winter and spring months; ...however, the timing and severity of circulating influenza viruses can vary by geographic location and season. Influenza viruses were detected in the United States throughout the summer months, and activity increased steadily during October and November. Most influenza viruses characterized thus far this season are well matched to the 2012-13 vaccine viruses. This report summarizes U.S. influenza activity* during September 30-November 24, 2012.†
During the 2012-13 influenza season in the United States, influenza activity* increased through November and December before peaking in late December. Influenza A (H3N2) viruses predominated overall, ...but influenza B viruses and, to a lesser extent, influenza A (H1N1)pdm09 (pH1N1) viruses also were reported in the United States. This influenza season was moderately severe, with a higher percentage of outpatient visits for influenza-like illness (ILI), higher rates of hospitalization, and more reported deaths attributed to pneumonia and influenza compared with recent years. This report summarizes influenza activity in the United States during the 2012-13 influenza season (September 30, 2012-May 18, 2013) as of June 7, 2013, and reports the recommendations for the components of the 2013-14 Northern Hemisphere influenza vaccine.
During the 2011-12 influenza season in the United States, influenza activity* occurred at low levels during October through December and increased in January and February before peaking in mid-March. ...Influenza A (H3N2) viruses predominated overall, but influenza A (H1N1)pdm09 (pH1N1) and influenza B viruses also circulated widely. This influenza season was mild compared with recent years, with a lower percentage of outpatient visits for influenza-like illness (ILI),† lower rates of hospitalizations, and fewer deaths attributed to pneumonia and influenza. This report summarizes influenza activity in the United States during the 2011-12 influenza season (October 2, 2011-May 19, 2012) and reports the recommendations for the components of the 2012-13 Northern Hemisphere influenza vaccine.
Influenza activity in the United States began to increase in mid-November, remained elevated through February 21, 2015, and is expected to continue for several more weeks. To date, influenza A (H3N2) ...viruses have predominated overall. As has been observed in previous seasons during which influenza A (H3N2) viruses predominated, adults aged ≥65 years have been most severely affected. The cumulative laboratory-confirmed influenza-associated hospitalization rate among adults aged ≥65 years is the highest recorded since this type of surveillance began in 2005. This age group also accounts for the majority of deaths attributed to pneumonia and influenza. The majority of circulating influenza A (H3N2) viruses are different from the influenza A (H3N2) component of the 2014-15 Northern Hemisphere seasonal vaccines, and the predominance of these antigenically and genetically drifted viruses has resulted in reduced vaccine effectiveness. This report summarizes U.S. influenza activity* since September 28, 2014, and updates the previous summary.
CDC collects, compiles, and analyzes data on influenza activity and viruses in the United States. During September 30, 2018-February 2, 2019,* influenza activity
in the United States was low during ...October and November, increased in late December, and remained elevated through early February. As of February 2, 2019, this has been a low-severity influenza season (1), with a lower percentage of outpatient visits for influenza-like illness (ILI), lower rates of hospitalization, and fewer deaths attributed to pneumonia and influenza, compared with recent seasons. Influenza-associated hospitalization rates among children are similar to those observed in influenza A(H1N1)pdm09 predominant seasons; 28 influenza-associated pediatric deaths occurring during the 2018-19 season have been reported to CDC. Whereas influenza A(H1N1)pdm09 viruses predominated in most areas of the country, influenza A(H3N2) viruses have predominated in the southeastern United States, and in recent weeks accounted for a growing proportion of influenza viruses detected in several other regions. Small numbers of influenza B viruses (<3% of all influenza-positive tests performed by public health laboratories) also were reported. The majority of the influenza viruses characterized antigenically are similar to the cell culture-propagated reference viruses representing the 2018-19 Northern Hemisphere influenza vaccine viruses. Health care providers should continue to offer and encourage vaccination to all unvaccinated persons aged ≥6 months as long as influenza viruses are circulating. Finally, regardless of vaccination status, it is important that persons with confirmed or suspected influenza who have severe, complicated, or progressive illness; who require hospitalization; or who are at high risk for influenza complications be treated with antiviral medications.
During the 2010-11 influenza season, influenza activity* first began to increase in the southeastern United States, and peaked nationally in early February. Compared with the previous pandemic year ...(2009-10), higher rates of hospitalization were observed for persons aged≥65 years during the 2010-11 season, whereas lower hospitalization rates were observed in younger populations than during the pandemic year. Overall, the percentages of outpatient visits for influenza-like illness (ILI) were lower during the 2010-11 season than the 2009-10 pandemic influenza season. In the United States, influenza A (H3N2) remained the predominant virus throughout the season; however, 2009 influenza A (H1N1) and influenza B viruses also circulated, and the predominant virus varied by U.S. Department of Health and Human Service (HHS) region and week. This report summarizes influenza activity in the United States during the 2010-11 influenza season (October 3, 2010-May 21, 2011) and describes the components of the 2011-12 Northern Hemisphere influenza vaccine.
During May 21-September 23, 2017,* the United States experienced low-level seasonal influenza virus activity; however, beginning in early September, CDC received reports of a small number of ...localized influenza outbreaks caused by influenza A(H3N2) viruses. In addition to influenza A(H3N2) viruses, influenza A(H1N1)pdm09 and influenza B viruses were detected during May-September worldwide and in the United States. Influenza B viruses predominated in the United States from late May through late June, and influenza A viruses predominated beginning in early July. The majority of the influenza viruses collected and received from the United States and other countries during that time have been characterized genetically or antigenically as being similar to the 2017 Southern Hemisphere and 2017-18 Northern Hemisphere cell-grown vaccine reference viruses; however, a smaller proportion of the circulating A(H3N2) viruses showed similarity to the egg-grown A(H3N2) vaccine reference virus which represents the A(H3N2) viruses used for the majority of vaccine production in the United States. Also, during May 21-September 23, 2017, CDC confirmed a total of 33 influenza variant virus
infections; two were influenza A(H1N2) variant (H1N2v) viruses (Ohio) and 31 were influenza A(H3N2) variant (H3N2v) viruses (Delaware 1, Maryland 13, North Dakota 1, Pennsylvania 1, and Ohio 15). An additional 18 specimens from Maryland have tested presumptive positive for H3v and further analysis is being conducted at CDC.
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