Flu activity is rising all across the United States earlier than is typically observed, according to data from the CDC . The latest such report published October 16 covering the week ending October 10 showed 5% of respiratory specimens tested nationally were positive for influenza, the virus that causes the flu. This rate was up from 3.9% the previous week.

Flu activity is highest in western states like California, Washington, Hawaii and Arizona. The particular subtype of influenza that is causing more than 96% of infections currently is the influenza A(H1N1)pdm09 virus.

Why Is Flu Activity Rising?

It is not entirely clear why flu activity is rising earlier than expected, with flu usually starting in October and ending in late April or early May. Flu cases have been on the rise since late August and early September. An important consideration could be the predominance of H1N1 causing the vast majority of infections.

Influenza viruses are constantly evolving and mutating, and it is possible that the influenza A(H1N1)pdm09 virus could have picked up a mutation that allows it to evade immunity from prior infections and past vaccinations. Scientists and public health experts are looking into this as a potential cause for the uptake in flu cases. Additional considerations for rising flu activity would include travel patterns, changes in indoor activity as well as changes in population immunity.

Will This Year’s Flu Vaccine Cover Influenza A(H1N1)?

This year’s flu vaccine is a trivalent vaccine , meaning it offers protection against three different strains of the flu: influenza A(H1N1), influenza A(H3N2) and influenza B(Victoria lineage). Whether the vaccine will provide strong protection against a possible mutated variant of the H1N1 subtype is not known, but the vaccine should at least provide some defense against it since the vaccine covers the influenza A(H1N1) subtype. Even when vaccines are not perfect matches against circulating strains or mutations of the virus, vaccination still reduce the risk of severe illness, hospitalization and death. Real-world effectiveness studies will provide a clearer assessment as the flu season progresses.

When Should Americans Get Vaccinated?

The CDC recommends that everyone six months of age and older get a flu vaccine unless there is a contraindication to the vaccine like a severe prior allergy. Vaccination is particularly important for some populations that are more vulnerable to severe illness such as children under the age of 5, the elderly, those with weakened immune systems and those with chronic medical conditions like diabetes and lung disease.

The ideal time to get vaccinated is usually by the end of October. It takes about 2 weeks for the body to develop full immunity from a vaccine, so vaccination by this time ensures full protection when the flu usually peaks by December.

Vaccination is the most important preventive measure, but additional precautions can also reduce transmission of the flu. Improving indoor ventilation, staying home when sick, avoiding sick contacts and washing hands regularly can all mitigate your risk from catching the flu.

If you have the flu and are experiencing shortness of breath, dehydration or have difficulty keeping food down, you should be evaluated by a healthcare provider immediately. Prescription antiviral medications like Tamiflu work best when started early, ideally within 48 hours of symptom onset.

The early rise in flu activity is a reason to prepare, not panic. Earlier flu activity across America does not necessarily mean flu will be more severe this year. Improving vaccine uptake and taking practical precautions can help reduce one’s risk of the flu as the season unfolds.