More flu cases hitting early this season

Flu is arriving earlier in Tucson and Pima County, raising the possibility that residents could face a larger wave of illness as holiday travel and indoor gatherings increase. In the latest figures shared by the Pima County Health Department, 51 flu cases were reported in one recent week, compared with 10 during the same period last year. That is roughly five times as many cases, and health officials say numbers like these typically would not appear until about two weeks later in the season.

The county has reported several signs of an early increase. In data covering Sept. 13 through 19, Pima County recorded 27 new cases, a 50% increase from the previous week, bringing the seasonal total to 4,546 cases. The different figures reflect separate reporting periods, but point in the same direction: influenza activity is building sooner than usual. Lindsay Kohler, who manages epidemiology for the Pima County Health Department, said the county normally expects cases to rise around this time, although this year’s increase began earlier.

Arizona and the broader Southwest are among the first parts of the country seeing elevated flu activity. National tracking indicates that infections began increasing in late August and early September, while the usual seasonal acceleration occurs closer to November. By Oct. 7, projections from the Centers for Disease Control and Prevention showed flu infections rising in all 50 states, with the highest activity concentrated in the western region that includes Arizona, California, Hawaii, Nevada, Alaska, Idaho, Oregon and Washington.

That regional pattern could matter for Tucson residents who plan to travel or host visitors in the coming weeks. Kohler said flu activity is beginning on the West Coast and in the Southwest before gradually moving across the country. Holiday travel can put people from areas with different levels of infection into the same airports, planes, homes and gatherings, creating more opportunities for the virus to spread. The early start means there may be less time than usual before the season reaches its strongest point.

National indicators are not entirely consistent, but they also show a notably early season. CDC data through Oct. 3 classified nationwide flu activity detected through wastewater as very low, although the agency said updates had a brief gap because of a new testing contract. At the same time, WasteWaterSCAN, a Stanford University led monitoring system, classified national flu activity as high because more communities were showing increased virus concentrations in wastewater. The system found influenza A in 60% of samples for the month as of Oct. 13, compared with 20% in October 2025, the earliest onset recorded in at least four years.

Laboratory testing showed that about 3.6%, or 1,435, of 39,317 flu tests reported during the week ending Oct. 3 were positive. Influenza A accounted for 97% of those confirmed infections, while hospitalizations remained low. The dominant subclade identified so far is A(H1N1)pdm09, the same virus associated with the 2009 swine flu pandemic. It is now considered part of typical seasonal flu circulation. Influenza A changes more quickly than other flu types, which is one reason vaccines are reformulated each year. Last season, a mutated form known as subclade K contributed to concern because it caused cases while evading the season’s targeted vaccine.

There is no indication in the available local information that this season’s flu is making people sicker than last year’s strain or is more likely to lead to hospitalization. Still, flu can be serious, especially for children, older adults, pregnant people, immunocompromised people and those with underlying conditions such as obesity and diabetes. Symptoms can resemble a common cold but often include a higher fever, sore throat, muscle aches, headache and, in some cases, gastrointestinal problems. Complications can include pneumonia, encephalitis, myocarditis and Guillain-Barré syndrome. Parents and caregivers are being urged to contact a medical provider early when influenza is suspected, particularly for children or people at higher risk.

Health agencies and medical organizations continue to recommend annual vaccination for everyone age 6 months and older, with limited exceptions for people with certain medical conditions. People 65 and older are advised to receive a higher-dose vaccine when possible. Updated flu vaccines are available in Arizona, and medical experts recommend getting vaccinated by the end of October. Because protection takes about two weeks to develop, the earlier activity in Pima County is another reason residents who have not received a shot may want to act soon. Children younger than 9 who have never been vaccinated against flu need two doses, given four weeks apart.

This year includes different vaccine technologies. The traditional vaccine uses an inactivated sample of the virus to stimulate an immune response, while an mRNA version is also available. Kohler said the traditional option can reduce the severity of illness, while the mRNA vaccine may provide a better chance of preventing infection altogether. Adults 18 and older can walk into a local pharmacy for vaccination, while parents should confirm requirements with a pediatrician or pharmacy before taking children. Along with vaccination, health officials recommend washing hands with soap and water for at least 20 seconds, avoiding shared utensils and personal items, staying home when sick, considering a mask when ill or in crowded settings, and limiting large indoor gatherings when respiratory viruses are spreading.