In mid-October 2017, influenza experts predicted that the 2017-18 US flu season would be particularly severe due to a variety of different factors, which we addressed in a previous Outbreak Thursday post. Unfortunately, this prediction may be coming to fruition, with the CDC now reporting widespread flu activity in 46 states (meaning at least half of the regions in each state are reporting outbreaks of influenza or increases in influenza-like illness), with severe cases and deaths being reported across the country.

Affected Populations

Most people who get sick with the flu experience only mild illness and do not need to seek medical care or be prescribed antivirals. However, certain high-risk populations—including children younger than 5 years old, adults 65 years and older, and pregnant women—are more susceptible to flu-related complications such as ear infections, pneumonia, and sepsis that could potentially result in severe illness or death. So far this season, the CDC has reported 13 pediatric deaths, and many states are reporting deaths in high-risk populations, including TexasPennsylvania, and California. In addition to deaths among high-risk populations, the number of deaths reported in people younger than 65 in California is particularly concerning—27 since October, which is 24 more than at the same time last year. Deaths are also occurring in younger populations in other states, including one high-profile case of an otherwise healthy but unvaccinated 21-year-old in Pennsylvania, who died recently of complications from the flu. In spite of the increased threat to “high risk” groups, these deaths highlight the dangers flu poses to everyone.

Suspected Strain

Most cases (~80%) thus far have been caused by the H3N2 influenza A strain, which tends to be more severe and cause more deaths in those who are very young or very old, as compared to other influenza A or B strains. Additionally, vaccines typically have lower efficacy against the H3N2 strain. Some health officials are reporting that the vaccine might only be 32% effective against this season’s circulating strains; however, suboptimal vaccine efficacy is not particularly unique to this flu season. In fact, last year’s influenza vaccine saw only 43% vaccine effectiveness against H3N2, which was also the predominant flu strain that year. This highlights the need for a universal influenza vaccine that protects against all influenza variants and that subverts the limitations of current vaccine production technology (eg, egg-adapted changes).

Impact on the Healthcare System

Emergency departments across the country are filling up with patients complaining of flu-like symptoms. For example, the UCLA Medical Center emergency department in Santa Monica saw more than 200 patients in one day—60 more than usual—most of which complained of flu-like symptoms. In other California counties, emergency room crowding has prevented ambulances from being able to quickly off-load patients, limiting their ability to respond to incoming 911 calls. In an effort to mitigate the patient surge, some hospitals, including in California and Florida, are setting up “flu tents” where nurses can triage patients with flu-like symptoms without tying up ED personnel and resources unnecessarily.

The intense flu season is also coinciding with a shortage of intravenous fluids, which are needed to treat those with severe influenza illness. These shortages are due, in part, to Hurricane Maria, which damaged manufacturing plants in Puerto Rico. Healthcare providers are now struggling to administer fluids and electrolytes without using IV fluids (eg, by mouth or via feeding tubes). Additionally, patients and providers are experiencing difficulty accessing the antiviral oseltamivir in some locations, which may be due to the increased demand for the drug in California.

It is possible that the 2017-18 flu season may appear to be more severe then previous seasons simply because it is peaking earlier. While flu incidence is typically at its highest around February, the northern hemisphere flu season can really peak anytime between October and April. Regardless of whether this flu season is actually worse or just seems that way, the current impact on the health system is substantial, and access to antivirals and common medical interventions such as IV fluids is of the utmost importance in terms of treating patients. Finally, this surge in cases illustrates the importance of getting your annual seasonal flu vaccination. Vaccines not only protect you, they can also help decrease disease transmission in the community, particularly to those who may be at higher risk for complications.


Photo: Transmission electron microscope image of H3N2 influenza A virions; courtesy of CDC/Dr. Fred Murphy

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.