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Flu cases have plateaued in recent weeks. zeljkosantrac/Getty Images
  • Cases of the flu have dropped rapidly since peaking at the end of December.
  • In recent weeks those numbers have plateaued rather than continued downward.
  • Experts indicate that there’s likely more to come before flu season finally tapers off.

Cases of the flu have fallen considerably since they peaked at the end of December, but they still remain elevated across the country. Will there be a second wave?

The latest trends from the Centers for Disease Control and Prevention show that cases of the flu appear to have leveled off rather than continue their downward trajectory. Lab-positive cases of the flu, one of several indicators that the CDC uses to assess seasonal influenza activity, are stable after trending upward last week. Meanwhile, other key indicators like flu-related hospitalizations and visits to healthcare providers are similar to weeks prior.

“We’re not out of the flu woods yet,” said Dr. William Schaffner, a Professor of Infectious Disease and Preventive Medicine at Vanderbilt University.

“There’s still plenty of flu out there and the anticipation is, as per usual, we will have flu through February and then it will really begin to taper during March,” he told Healthline.

Of course, flu isn’t the only respiratory illness circulating right now either. COVID-19 and respiratory syncytial virus infection (RSV) are still highly active as well. According to the latest CDC numbers, there have been more than 133,000 emergency department visits nationally due to these three combined. Influenza is still the greatest driver, though, causing roughly 79,000 of those emergency room visits.

There’s good reason to expect another bump in flu cases this year. Historically, influenza activity most often peaks in February, before finally falling off.

“I don’t have a great crystal ball, but it wouldn’t surprise me if we saw fairly high case numbers through mid-March,” said Dr. Dean Winslow, a Professor of Medicine at Stanford Medicine and infectious disease expert.

The 2023-2024 flu season has also been one of the most robust since the COVID-19 pandemic in 2019-2020.

Last year’s flu season was also strong, but it peaked much earlier, at the end of November, before crashing precipitously in December and January.

This year, the season appears to have peaked in the last week of December.

Right now flu cases are much higher than at the same time last year.

“In general, the country has seen a diminution in new cases of influenza, but it’s still way above the annual epidemic level. Our influenza cases are down somewhat, but they’re on a plateau, basically. They’re maintaining themselves,” said Schaffner.

Monitoring the extent and severity of flu season is complex.

There are also important regional variations in flu activity across the United States. Southern states including Texas, New Mexico, Arkansas, Louisiana, and South Carolina are all showing very high levels of flu activity. Meanwhile, many western states, from Colorado to Oregon show moderate to low levels.

In order to establish what a national snapshot looks like, scientists at the CDC have to use a variety of indicators.

For example, this week the number of laboratory-confirmed positive influenza cases sits at 15.8%. Out of more than 96,000 tested specimens, about 15,000 of them tested positive for the flu. The percentage of laboratory-confirmed tests has also been relatively stable for the past several weeks.

Another indicator, reported flu-related doctor visits, is at 4.4%. That means that out of all cases reported through one of the CDC’s respiratory illness surveillance programs, 4.4% met the definition of an “influenza-like illness” or ILI. An ILI is defined as a fever of 100 degrees or more, accompanied by cough and/or sore throat.

Deaths due to the flu have also been falling in recent weeks. There were 222 flu-related deaths in the past week, compared to 490 the week before.

Like all viruses, the flu is prone to mutation, meaning that one flu season will differ from the next in terms of severity of symptoms and transmissibility. While there are four types of influenza viruses (A, B, C, and D), the first two are responsible for the annual flu season epidemic in the United States.

Influenza A makes up the bulk of cases year after year, while influenza B makes up a much smaller proportion of illnesses.

“There’s an old adage, if you’ve seen one flu season, you’ve seen one flu season. It’s usually the case that influenza B plays a minor role earlier in the annual outbreak and then becomes more prominent as we get through February into March,” said Schaffner.

This year’s virus, “influenza A(H1N1)pdm09,” might sound familiar to some readers. That H1N1 designation is one you’ve seen before.

“This particular strain of flu is very similar to the H1N1 virus which caused the catastrophic ‘Spanish Flu’ pandemic of 1918-19,” said Winslow.

“Interestingly, during the 1918-19 Spanish flu, a lot of cases were seen late in the season also,” he added.

H1N1 is a swine flu subtype of influenza A virus that, in addition to the famous 1918 pandemic, was also responsible for an outbreak in 2009-2010. At that time, it is estimated that the virus was responsible for somewhere between 43-89 million cases across 178 countries.

The number one thing you can do to stay well during this flu season is to get a flu shot. Both Winslow and Schaffner recommend getting one, especially if you fall into a high-risk category. Individuals who are 65 years of age or older, children younger than 5, pregnant, or have certain chronic conditions are considered at higher risk from flu-related symptoms.

Other important considerations for staying well include minimizing time spent in large groups indoors and social distancing.

Flu season isn’t over yet. Cases are overall down from their peak at the end of December but are still considerably elevated nationally.

Cases have plateaued, but February is historically one of the peaks of flu season, and there is the potential for another wave.

Experts recommend getting a flu shot, avoiding large indoor group activities, and social distancing to stay safe from the flu this season.