November 19, 2021—While overall flu activity is still low in the United States, the number of laboratory-confirmed influenza infections continue to increase. More than 90 percent of the cases have been detected in children and young adults, and CDC’s system for monitoring influenza-like-illness (ILI) shows hot spots of activity in several urban centers home to large colleges or universities.

While most of the laboratory-confirmed influenza infections have been influenza A(H3N2) virus infections, laboratory data suggest ILI activity is a result of varying levels of flu and other respiratory viruses.

Don’t take flu home for the holidays, get a flu vaccine to prevent the spread of flu.

As young adults with flu travel for the Thanksgiving holiday, this could set off community-wide spread across the country. This situation underscores the importance of ongoing seasonal flu and COVID-19 vaccination efforts as well as that people be proactive about taking other precautions for their own health and the health of others. Given the timing of the fast-approaching Thanksgiving holiday and the fact that it takes two weeks for immunity from vaccination to set in, people should get vaccinated as soon as possible and also take everyday preventive actions to reduce the spread of respiratory illness like flu. These everyday preventive actions include staying home when sick, covering coughs and sneezes, and washing your hands often. While CDC does not recommend routine use of masks for seasonal flu in the community setting, it is recommended for prevention of COVID-19 at this time.

On college campuses, flu viruses are known to spread rapidly in close quarters like common living spaces, classrooms, shared restrooms, and through social activities. Despite this, young adults consistently have the lowest flu vaccination coverage every flu season in the United States. For example, a CDC Epi-Aid that is supporting a local investigation into an outbreak of H3N2 flu at the University of Michigan in Ann Arbor has found nearly 700 students, faculty and staff have tested positive for influenza since October 6, 2021, but only about one-quarter of them had been vaccinated.

CDC also has anecdotal reports of flu outbreaks at other colleges and universities across the country. Many of these coincide with urban centers and economically linked surrounding areas (technically called “core-based statistical areas”) that are showing elevated ILI. It’s important to note that ILI visits do not necessarily represent influenza virus infection. ILI visits include patients who present with a fever (temperature of 100°F [37.8°C] or greater) and a cough and/or a sore throat. These symptoms can result from infection with a number of different viruses, including SARS-CoV-2; therefore, it’s important to look at laboratory data for flu or other respiratory viruses in combination with ILI data to get a complete picture of influenza and other respiratory virus activity. Laboratory data from public health and clinical laboratories suggest that flu is contributing to some, but not all of these hotspots of ILI. In addition to showing areas where ILI is elevated, CDC’s FluView interactive displays flu laboratory data nationally, by HHS Region, as well as by state, so that people can track where influenza viruses have been detected.

Looking to the holidays and beyond, there’s still time to benefit from a flu vaccine this season. Flu activity is just beginning and while unpredictable, most often peaks between December and February and can last into May. A flu vaccine protects against four flu viruses, including an H3N2 virus that was updated for this season’s flu vaccines. Getting a flu vaccine has many benefits. In addition to helping prevent flu illness, several studies have shown flu vaccination reduces the severity of illness in people who get vaccinated but still get sick. Flu vaccination also can help protect others. Much of the U.S. population is at higher risk of developing serious flu illness, including people 65 and older, young children, people with certain chronic conditions and pregnant people. Flu can be more serious for them. While people at higher risk should get vaccinated, if the people around them get vaccinated too, that can provide a cocooning effect, where vaccinated people can help form a “cocoon” of disease protection. Initial CDC estimates of flu vaccine uptake this season suggest that flu vaccination coverage is lower compared to the same time last season among certain groups of people.

For people who develop flu symptoms, which can overlap with those of other respiratory viruses, there are tests that can distinguish between flu and other viruses, including COVID-19, for example. It’s important to remember that there also are drugs to treat flu illness. CDC recommends prompt treatment with a flu antiviral drug for people who have flu or suspected flu and who are at higher risk of serious flu complications. Antiviral drugs are not a substitute for getting a flu vaccine. While flu vaccine can vary in how well it works, a flu vaccine is the best way to help prevent seasonal flu and its potentially serious complications. Antiviral drugs are a second line of defense that can be used to treat flu if you get sick. CDC recommends that people at higher risk of developing serious flu complications get antiviral treatment as early as possible, because benefit is greatest if treatment is started within 2 days after illness onset.

It’s also important to remember COVID-19 vaccines will not prevent flu illness and vice versa. Flu vaccines protect against flu viruses, and COVID-19 vaccines protect against the virus that causes COVID-19. So, one vaccine is not a substitute or a replacement for the other. Both vaccines are recommended, and it’s important that people be up to date on their recommended flu and COVID-19 vaccines. For adults and most children, a single dose of flu vaccine is needed annually for everyone 6 months and older. Flu vaccines and COVID-19 vaccines can be given during the same visit.

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