This Flu Season Could See More Severe Illness Among Children and Older Adults

CDC update

January 12, 2024 — As seasonal flu activity remains elevated nationally, CDC is tracking when, where and what influenza viruses are spreading and their impact on the public's health. So far this season, the most commonly reported influenza viruses are type A(H1N1) and type B viruses. According to CDC research, this could mean more severe outcomes among people who are hospitalized with flu.

A CDC study published in November in The Lancet Microbe looked at outcomes by influenza type and subtype from 2010 to 2019 among more than 100,000 people hospitalized with influenza illness. Despite a higher number of hospitalizations caused by flu A(H3N2) viruses, patients who were hospitalized with flu A(H1N1) or B viruses had a higher likelihood of severe in-hospital outcomes compared with people who were hospitalized with flu A(H3N2) virus infections, the study found. More severe outcomes could mean greater demand for advanced medical care in the intensive care unit (ICU), such as mechanical ventilation, which could strain health care resources.

The reasons for increased odds of severe illness with influenza A(H1N1) or influenza B viruses are unclear, but all seasonal influenza viruses can cause severe illness, and it's important that people take precautions to protect themselves against influenza when any seasonal influenza viruses are spreading. Unfortunately, flu vaccination coverage is currently lower among children by 5.3% and among adults by 3% compared to the same time last year. That amounts to an estimated 10 million fewer people being vaccinated this season, leaving that many more people at risk of influenza infection and serious complications.

CDC estimates that there have been at least 150,000 hospitalizations and 9,400 deaths from flu so far this season. Forty laboratory-confirmed pediatric deaths have been reported to CDC, 13 of which were reported on Friday, January 12. In past seasons, about 80% of children who died from flu have not been fully vaccinated. Twenty-two of these deaths were associated with influenza A viruses (11 H1N1, 2 H3N2, 9 were not subtyped) and 18 were associated with B viruses.

While influenza A(H1N1) viruses are predominant, followed by influenza B viruses, the distribution of influenza viruses varies by region. The good news is that most of the influenza viruses spreading so far this season are well-matched by those represented in this season's flu vaccines, which suggests vaccination should offer good protection. Findings of studies looking at vaccine effectiveness this season will be available in February.

Getting vaccinated can reduce your risk of getting sick with flu and make your flu illness less severe if you do get sick. Even if you already got flu this season, vaccination can still protect you from getting sick with other influenza viruses that are spreading since flu vaccines protect against multiple flu viruses. Vaccination may also help protect people around you, including those who are at higher risk of serious flu illness, like babies and young children, older people, pregnant people, and people with certain chronic health conditions. Everyone 6 months and older should get a flu vaccine each year for the best protection against flu.

CDC also recommends prompt treatment with an influenza antiviral medication for people who have flu or suspected flu and who have severe illness (are hospitalized) or who are at higher risk of serious flu-related complications. When treatment is started within two days of becoming sick with flu symptoms, antiviral drugs can lessen fever and flu symptoms and shorten the time you are sick by about one day. They also may reduce the risk of some complications such as ear infections in children, respiratory complications requiring antibiotics, and hospitalization in adults. Antiviral drugs are not sold over the counter. You can only get them if you have a prescription from a health care provider.

CDC also is tracking hospital capacity this respiratory virus season.