NEWS ANALYSIS

Flu By the Numbers: January 22, 2022

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During the COVID-19 pandemic, the Centers for Disease Control and Prevention (CDC) suspended data collection and assessment of influenza cases in the United States for the 2020-2021 flu season.

As a result, current statistics may not capture the full picture of flu activities. For example, the cases and deaths might be undercounted, and data from some states might be inconsistent or delayed.

In any flu season, the data that gets reported by the CDC each week is always preliminary and it can change as new information becomes available.

As of January 22, 2022, the CDC reported increasing influenza-like illness (ILI) activity in most of the United States. At the end of the week of January 15, levels of ILI activity went down slightly in most states but are expected to rise in the coming weeks.

The number of people going to the doctor for or being hospitalized for respiratory illness is also rising. The flu is responsible for some of these cases.

Centers for Disease Control and Prevention

Clinical laboratories in the U.S. tested 91,206 specimens for flu viruses, of which 1.8% were positive. Among the positive results, 98.6% were for influenza A.

Public health laboratories in the U.S. also reported data about specimen testing to the CDC. Of the 54,157 samples tested, 575 were positive for the flu.

Influenza patterns vary according to the specific flu virus strains that are circulating in a given year, as well as human behavior. For example, some of the changes that the pandemic brought about—such as mask wearing and social distancing—slowed down the flu spread last year.

Another factor that affects flu patterns is vaccination. Annual flu vaccines are a safe and effective way to help curb the spread of the flu and to prevent hospitalizations and deaths.

Flu Vaccine Doses Given

As of December 17, the CDC reports that more than 173 million flu vaccine doses have been distributed in the U.S.

What Information Do States Report?

The CDC tracks LIL activity levels in each state and presents a weekly flu surveillance report. LIL activity levels are defined as the following:

  • Minimal (levels 1-3)
  • Low (levels 4-5)
  • Moderate (levels 6-7)
  • High (levels 8-10)
  • Very High (levels 11-13)

State health departments track flu data provided by hospitals, clinics, clinical laboratories, and healthcare organizations. These reports can include information like the number of flu tests conducted, positivity rates, and the number of flu-like illnesses that providers saw in the patients they treated.

What Can The Data Tell Me About Flu Activities In My State?

Data on ILI activity can give you a sense of how many people have respiratory symptoms in your state.

If the activity level is high in your area, it could mean that the flu is "going around" in your community. You can be more cautious and take preventive steps, such as washing your hands frequently and getting a flu shot, to help reduce veryour risk of getting sick.

If you're showing flu-like symptoms yourself, call your physician to see if you should go in for a test. In the meantime, you can take antiviral medications such as Tamiflu to help lessen your symptoms. You can wear a mask and avoid close social contact to stop the spread.

How Is Flu Data Different From COVID-19 Data?

The flu and COVID-19 are different, though they do have similar symptoms that can make it hard to tell them apart. One of the key ways that we can keep track of all the data is by testing people who have symptoms to find out if they have the flu, COVID, or another kind of respiratory illness.

Clinical labs (like those used by doctor's offices and hospitals) and public health departments both test specimens to look for signs of the flu, but each has a different goal.

Clinical labs are more geared toward providing a flu diagnosis (or ruling out the flu) while public health labs are looking at the larger trends in flu illness—for example, which subtypes of the flu are circulating and how quickly cases of the flu are growing in different places and among different groups of people.

Public health departments often test samples that were already tested in clinical labs to look for a diagnosis, which is why the CDC tracks specimens tested by each type of lab separately to make sure that the numbers are not duplicated (if they were, it could make it seem like there is more flu activity in a community than there really is).

Some specimens tested for the flu might also be tested for COVID at the same time, or, if the flu test is negative, a person might need a COVID test next. This will probably be more common in the winter months when both types of viruses end up circulating at the same time.

Eventually, we may reach a point where we have a recurring "COVID season" like the annual flu season. For now, public health authorities are trying to follow both illnesses as they move through communities and report the data separately.

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