Maine’s flu season has been milder and peaked later than in 2014-15.

About 60 percent of the 1,398 positive flu tests reported to the Maine Center for Disease Control and Prevention in 2015-16 occurred between March 6 and April 2, according to the latest weekly statistics reported on the Maine CDC website. That compares to the 4,233 flu cases reported in the 2014-15 flu season, when the peak occurred two months earlier. There were 2,029 cases in 2013-14 and 167 cases in 2012-13. The flu season runs from October through May.

Nationally, there have been about 45,000 positive tests for flu so far this season, and the U.S. Centers for Disease Control and Prevention is reporting that the season already has peaked and is declining in most places.

In Maine, the 2015-16 flu season is shaping up to be mild, especially in contrast to the previous year.

The cause of the recent surge in cases is unclear.

“We don’t know why there has been a spike in the number of influenza cases in the past few weeks,” Dr. Siiri Bennett, the state epidemiologist for the Maine CDC, wrote in email response to questions Tuesday.

She said flu vaccine is still available and people can still get immunized, even this late in the season. Doctor’s offices, health clinics and pharmacies typically have vaccines in stock, but customers should call in advance to be sure.

Dr. Dora Anne Mills, a former Maine CDC director and vice president of clinical affairs at the University of New England, said that flu season is notoriously unpredictable.

“You can have a flu season peak late in the season. The flu can peak at any time,” Mills said.

Mills attributes the relatively mild season to the effectiveness of the vaccine.

Each year, U.S. Food and Drug Administration scientists anticipate which strains of influenza virus are likely to be circulating and manufacture a vaccine to protect against them. Predicting which strains of virus will be present in future months is an educated guess, Mills said, despite the best efforts of scientists.

While the vaccine for 2014-15 was only about 20 percent effective, according to the U.S. CDC, this year’s vaccine is 59 percent effective in preventing flu.

Mills said regardless of the effectiveness of the vaccine in any given year, there are health benefits to getting the vaccine annually. People who get their vaccines every year or most years give their bodies the best chance to fight off viruses, as the immune system “remembers” past vaccines, she said.

York County has been hardest hit with flu cases this season, with 309 of the total 1,398 positive tests reported in Maine’s southernmost county. Cumberland County had the second-most cases, with 258.

Martin Sabol, clinical director at Nasson Health Care in Sanford, a community health clinic, said they haven’t seen an influx of flu cases over the past month, but the clinic frequently promotes the flu shot to its patients. Also, the clinic doesn’t typically service many elderly or pediatric patients, who are more susceptible to the flu.

“We take vaccination very seriously, and flu vaccines are offered to everyone age 6 months or older,” Sabol said.

The flu has led to 205 hospitalizations in Maine this season, including 44 new cases last week. The age of those hospitalized ranged from 3 months to 94 years, with an average age of 56. One child under age 5 who had not been vaccinated died as a result of the flu, the CDC data shows. The agency did not publish hospitalization data last season.