After taking a hiatus last season, the influenza virus has returned to Maine, although it has gotten off to a slow start, reflecting a national trend.

The Maine Center for Disease Control and Prevention released its weekly influenza surveillance report Tuesday, which says 13 people have been hospitalized with the flu since the season began in late September.

There have been no confirmed flu deaths so far this year, though there is often a lag in reporting because deaths must be confirmed via death certificate review. There have been 505 positive influenza cases reported this season by Maine-based labs, according to the Maine CDC.

But although the flu season has gotten off to a slow start, it is unclear what will happen in the weeks ahead as as more people congregate indoors where transmission is most likely to occur, Dr. Dora Anne Mills, MaineHealth’s chief health improvement officer, said Tuesday.

The federal Centers for Disease Control and Prevention, which monitors influenza transmission nationally, is reporting that activity is still low, but that a pattern of steady increases is emerging.

In Maine, nearly all positive tests have been for influenza A’s H3N2, a highly virulent strain, and that mirrors national data, according to the federal CDC. Most infections have occurred among people age 5-24, but the rate among adults age 25 years and older has been increasing, the CDC said.

“We are seeing a more virulent strain of influenza circulating here in Maine and in the United States, which generally causes more hospitalizations,” Mills said. “The good news is the flu vaccine is readily available and it seems to be a pretty good match for the flu virus.”

A map of influenza cases published this week by the federal CDC indicates that transmission is high in New Jersey, the District of Columbia, Indiana, Kansas, North Dakota and New Mexico.

Although COVID-19 and influenza symptoms tend to be similar, Mills said, the most prominent flu symptom is intense body aches while the hallmark symptom of COVID is the loss of taste and smell.

“When you get the flu, you feel like you got hit by a truck,” Mills said.

Individuals who test negative for COVID should ask their health care providers to test them for flu, Mills said. The flu test is ready available, usually involves a nasal swab and there are remedies available for reducing flu symptoms, such as the prescription drug  Tamiflu.

Influenza took last year off, Mills said. In late March, nearly three-quarters of the way through the 2020-21 flu season, there had been just 136 total cases reported and only three hospitalizations, according to the Maine CDC. There were no outbreaks or deaths.

In March 2020 – just as the pandemic was starting to take root – there already had been 36 flu deaths, 81 outbreaks, 494 hospitalizations and 10,000 cases. By mid-March 2018, during Maine’s worst flu season in recent memory, there had been 6,973 seasonal flu cases, 1,326 hospitalizations, 122 outbreaks and 71 deaths.

Health experts say the precautions people took against COVID-19 a year ago, including social distancing, wearing masks and washing hands, likely caused the dramatic drop in flu cases. In addition, more residents got the flu vaccine in 2020.

Health officials are not sure what to expect in the weeks ahead as Maine and the country head into a season where influenza and COVID will be circulating simultaneously.

“It’s anybody’s guess as to what is going to happen with flu season this year,” Mill said. “We didn’t have a flu season last year and we don’t know why. We may not know for awhile.”

In Mills’ view there is only one reliable method of protecting yourself from the flu and COVID.

“Getting vaccinated for the flu and COVID is the best course of action,” Mills said.

Flu season typically starts in late September and early October and can run into May. Flu cases usually peak between December and February, according to the federal CDC.