U.S. Flu Season Is Here, CDC Urges Vaccination

January 3, 2014 – Significant increases in flu activity in the United States have occurred in the last couple weeks and this week 25 states are reporting widespread flu activity while another 20 are reporting regional activity, indicating that flu season is definitely here. CDC is urging all those who have still not gotten their flu vaccine to get vaccinated!

According to CDC’s influenza surveillance report published on January 3, 2014 (Week 52), all 50 states, Puerto Rico, and the District of Columbia have reported cases of laboratory-confirmed influenza and, nationally, the percentage of specimens testing positive for influenza continues to rise, up from 13.3% in the week ending December 14, 2013, to this week’s 26.7%. (Regional percentages this week range from 11% to nearly 35%)

Influenza-like-illness (ILI) activity, or the percentage of patients that visited doctors for flu-like symptoms, is also on the rise. Nationally, the United States reached the baseline level for ILI during the week ending December 7, 2013 (Week 49), and this week 20 states are reporting high ILI activity. (The baseline coincides with the point at which the ILI activity is most likely caused by influenza and not other respiratory viruses.) These increases, together with other indicators of influenza activity, are a good sign that flu season is well under way. However, some of the reported ILI increase may be related to a temporary reduction in the number of all health-related visits people made to health care providers during the holidays. During the holidays the number of routine visits to doctors tends to decrease and therefore a higher proportion of visits are more likely to be sick-visits for things like influenza-like illness. This, in combination with increasing levels of influenza in the community, leads to much higher levels of ILI.

According to FluView, flu activity to date has been most intense in the south-central and southeast of the country, although now activity is increasing across the rest of the country as well. Most of the viruses characterized so far this season have been 2009 H1N1 viruses (‘pH1N1’ viruses), which have circulated worldwide as seasonal flu viruses since the influenza pandemic in 2009. During the pandemic, younger adults and children, and particularly people with chronic medical conditions and pregnant women, were harder hit by pH1N1 compared with adults aged 65 and older. While it’s not possible to predict which influenza viruses will predominate for the entire 2013-2014 influenza season, if pH1N1 virus continues to circulate widely, illness that disproportionately affects young and middle-aged adults may occur this season.

Two new influenza-associated deaths in children are reported in this week’s FluView, bringing the current total to six for the 2013-2014 season. Last week CDC issued a Health Advisory that discusses recent reports of severe influenza infection associated with pH1N1.

CDC is also reporting a small increase in the rate at which flu-related hospitalizations are occurring: 5.8 per 100,000 population, up from 4.9 per 100,000 in Week 51. Among hospitalizations where flu virus type was laboratory-confirmed, over 98% of hospitalizations were associated with pH1N1 virus infection. For comparison purposes, last season the hospitalization rate in Week 52 was 13.3 per 100,000, and in 2011-2012, the hospitalization rate at this time was 0.4 per 100,000. (The rate of hospitalization is a cumulative number, and rises as a season progresses.)

These severe flu outcomes are a reminder that flu can be a serious disease for anyone, including otherwise healthy people: CDC recommends yearly vaccination as the best protection. This season’s flu vaccine is designed to protect against three to four influenza viruses, depending on which vaccine you get. All of the vaccine options this season include protection against pH1N1.

Everyone aged 6 months and older should get a flu vaccination each year to protect themselves and their loved ones against the flu. Vaccination is especially important for people who are at high risk of serious flu-related complications, like young children and people 65 and older, pregnant women, and people with certain chronic medical conditions, like asthma, diabetes and heart disease.

People who are at high risk for influenza complications should see their health care provider promptly if they get flu symptoms. A health care provider can determine if the patient needs influenza antiviral drugs. Antiviral drugs can treat flu illness and prevent serious flu complications.

More information is available on the CDC Seasonal Influenza (Flu) website.