Flu cases are climbing nationwide, with nearly 50 deaths reported in recent days

One strain tied to the swine flu pandemic is driving an unusually early surge this season

As flu cases rise across the country, nearly 50 people have died from the illness in the past week, prompting warnings that the respiratory virus season has begun earlier than usual.

In Connecticut, state health officials said six people have died from the flu since late September. All of the unidentified patients were older than 55, according to the state health department.

"These deaths are a sobering reminder that flu can be serious, especially for older adults, and that respiratory virus season is already here," state health commissioner Dr. Manisha Juthani said in a statement.

The state’s first flu death of the season came about a month earlier than in the previous flu season, reflecting a broader national pattern.

Flu activity, with roughly 5,600 cases so far this season, has been rising more than two months earlier than normal. Peak season typically falls between December and February. In the past week, 47 flu-related deaths have been confirmed nationwide, with more expected.

According to the Centers for Disease Control and Prevention, flu causes between 9.4 million and 51 million illnesses each year and leads to about 6,300 to 52,000 deaths.

The CDC does not yet list child flu deaths on its tracker, but reports say two have been recorded in San Diego and one in Colorado, where University of California Health says positive tests are running six times higher than at the same point last year.

Federal data indicates that a single strain is responsible for most cases. H1N1, the virus behind the 2009 swine flu pandemic, accounted for the majority of cases in the latest week of data, which ended on October 10.

This season’s flu vaccine targets H1N1, along with the B/Victoria virus and subclade K, a form of H3N2 influenza that also circulated last year.

Most seasonal flu cases are caused by influenza A strains, including H3N2 and H1N1. Early evidence suggests this year’s vaccine is a strong match for the H3N2 variant, Scott Hensley, a University of Pennsylvania microbiology professor, told NBC News.

Although the H1N1 variant has developed new mutations that help it evade some immunity in communities, "data suggest this year's influenza vaccine can recognize this variant, so the immune escape is only partial, or rather incomplete," said Andrew Pekosz, a professor at the Johns Hopkins Bloomberg School of Public Health.

"Right now, there is no cause for concern, but this should be viewed as a good last call to get your influenza vaccination for this year because vaccines work best when taken before the influenza season starts," he said.

Even when protection is not perfect, vaccination still helps reduce the risk of severe illness and death.

There is also a delay before the shot becomes fully effective, so the sooner people get vaccinated, the better — especially before the holidays and colder weather increase the risk of indoor spread.

"It takes about two weeks for the body to build protection, and getting vaccinated now will help provide protection for the holiday season when people gather indoors," Juthani said.

Although flu season usually stretches from fall into spring, it is still worthwhile to get a flu shot later in the season if needed.