A new strain of whooping cough has been discovered. Researchers have found that the cough is caused by a germ that is resistant to the vaccine.

ABC News reported that health officials are looking onto whether the cases that have been reported might be one reason why the U.S. had its worst year in whooping cough in nearly 60 years. This new strain was also previously reported in France, Finland and Japan.

"It's quite intriguing. It's the first time we've seen this here," said Dr. Tom Clark of the Centers for Disease Control and Prevention to ABC News.

Whooping cough is a contagious disease that can occur at any age but is most dangerous to children. Cases of whooping cough have dropped since a vaccine was introduced in the 1940s.

"An increase in illnesses in recent years has been partially blamed on a version of the vaccine used since the 1990s, which doesn't last as long. Last year, the CDC received reports of 41,880 cases, according to a preliminary count. That included 18 deaths," said ABC News.

The new study soon to be published in the New England Journal of Medicine says that the new strain of whooping cough may be the reason why more people have been getting sick.

"The organism has adapted to evade one part of the immune response," Dr. Alan Evangelista, Director of Microbiology at St. Christopher's Hospital for Children to NBC News, "It may be a contributing factor for the rise in the number of cases."

"Whooping cough gets its name for the whooping sound an infected person makes when they cough. The upper respiratory infection is highly contagious and can be spread quickly through coughing or sneezing.

Dr. Evangelista says whooping cough cases jumped nationwide last year to levels not seen in more than half a century," reportd NBC News.

To find the new strain of whooping cough researchers collected samples from patients and found that in 11 cases there was a pertussis bacteria that was no longer producing "one of three elements -- a protein called pertactin -- which the immune system uses to identify and fight the disease," reported NBC News.

"So your lineman and your linebacker can see the bacteria, but the safeties and cornerbacks don't see it," Dr. Evangelista added.

The goal of research is to increase awareness and improve the vaccine if possible.