Avian Flu Diary: CDC FluView Week 5: Seasonal Flu Rising Again

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After appearing to peak in early January (which may be an artifact of delayed reporting), flu levels are once again rising (see chart below), reaching the highest level reported in the past 5 years.

While no new H5 cases have been reported in recent weeks, the CDC is reporting the first (swine) variant (H1N2v) detection of 2025.

Key Points

• Seasonal influenza activity remains elevated and continues to increase across the country.

• During Week 5, of the 4,377 viruses reported by public health laboratories, 4,264 were influenza A and 113 were influenza B. Of the 3,458 influenza A viruses subtyped during Week 5, 1,857 (53.7%) were influenza A(H1N1)pdm09, 1,601 (46.3%) were A(H3N2), and 0 were A(H5).

• Outpatient respiratory illness is increasing and remains above baseline nationally for the tenth consecutive week. All 10 HHS regions are above their region-specific baseline.

• One human infection with an influenza A(H1N2) variant (A(H1N2)v) virus was reported.

• No new influenza A(H5) cases were reported to CDC this week. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States.

• Ten pediatric deaths associated with seasonal influenza virus infection were reported this week, bringing the 2024-2025 season total to 57 pediatric deaths.

• CDC estimates that there have been at least 24 million illnesses, 310,000 hospitalizations, and 13,000 deaths from flu so far this season.

• CDC recommends that everyone ages 6 months and older get an annual influenza (flu) vaccine.1

• There are prescription flu antiviral drugs that can treat flu illness; those should be started as early as possible and are especially important for patients at higher risk for severe illness.2

• Influenza viruses are among several viruses contributing to respiratory disease activity. CDC is providing updated, integrated information about COVID-19, flu, and respiratory syncytial virus (RSV) activity on a weekly basis.

Swine variant infections are generally mild or moderate in severity, and are indistinguishable from regular flu without a lab test. Most are linked to direct or indirect contact with swine, often at agricultural exhibits and county fairs, although (as in the case of today's case), sometimes no known exposure is reported.

Novel Influenza A Virus Infections

One human infection with influenza A(H1N2) variant (A(H1N2)v) virus was reported by the Iowa Department of Health and Human Services.

The patient is ≥18 years of age and sought health care during the week ending January 18, 2025 (Week 3), was hospitalized, and has recovered from their illness. An investigation by state public health officials did not identify direct or indirect swine contact by the patent. No illness was identified among the patient's close contacts. No human-to-human transmission has been identified associated with this case.

This is the first human infection with a variant influenza virus reported during the 2024-2025 season in the United States.

When an influenza virus that normally circulates in swine (but not people) is detected in a person, it is called a "variant" influenza virus. Most human infections with variant influenza viruses occur following exposure to swine, but human-to-human transmission can occur. It is important to note that in most cases, variant influenza viruses have not shown the ability to spread easily and sustainably from person to person. Additional information on influenza in swine, variant influenza virus infection in humans, and guidance to interact safely with swine can be found at www.cdc.gov/flu/swineflu/index.htm.

No new human infections with A(H5) were reported to CDC this week. An ongoing outbreak of H5N1 continues in domestic dairy cows and poultry, and monitoring for additional human cases is ongoing.

Although the public health risks from swine variant viruses are considered low, the CDC advises those who are at higher risk of serious flu complications (including children under 5, adults over 65, pregnant women, and those with certain chronic medical conditions), to avoid pigs and the swine barn altogether.

In 2023 the CDC held a webinar for clinicians on recognizing, treating, and reporting zoonotic influenza cases in the community (see COCA Call : What Providers Need to Know about Zoonotic Influenza), which remains available on their website.

Since there are likely to be several more weeks of heavy flu activity still ahead of us, there may still be value in getting the flu (and COVID) vaccines, and face masks and hand sanitizer can add prudent additional layers of protection.