Public health officials are warning the U.S. that this year's flu season could be worse than usual, according to the Association of Health Care Journalists.

Australia had a tough flu season during its winter, which ended Aug. 31. Healthcare providers in the U.S. typically predict how the U.S.'s flu season will go based on what happened in the Southern Hemisphere and on informed, educated guesses.

"We don't know what's going to happen, but there's a chance we could have a season similar to Australia," Dr. Daniel Jernigan, influenza chief at the Centers for Disease Control, told the Associated Press.

Australia has not yet collected all its data from flu season, but there might be evidence suggesting the flu vaccine was less effective than is typical. Initial data has also suggested more adults and children contracted the flu than in recent years.

About 5% to 20% of the U.S. population comes down with the flu each year. During the 2016 flu season, which was broadly characterized as moderate, more than 600,000 were hospitalized as a result of complications from the flu, according to the CDC.

"I like to say flu is fickle. I am often asked 'how severe will the season be?' It will be severe and it will always be severe," Vanderbilt University School of Medicine professor Dr. William Schaffner said. "Flu vaccination is our first and best line of defense to prevent flu."

Last year, the U.S. flu vaccine was about 42% effective, which means people who got the shot were 42% less likely to need additional medical care due to the flu.

Although anyone who suffers the flu isn't gaining much, some stocks are set to capitalize on a tough flu season.

Walgreens Boots Alliance Inc. (WBA - Get Report) and CVS Health Corp. (CVS - Get Report) could see increased traffic as flu shot season moves into full swing. The two drug stores chains, along with Target Corp. (TGT - Get Report) and Walmart Stores Inc. (WMT - Get Report) , might see an uptick in pharmacy sales as patrons gobble up prescription strength flu treatments.

Procter & Gamble Co. (PG - Get Report) owns Vicks over-the-counter medicine brand, which might become a popular brand in the fall and winter months. Vicks manufactures cold treatments including DayQuil and NyQuil, Formula 44 cough drops and Vicks VapoRub.

Also set to make a buck on a nasty flu season are Johnson & Johnson (JNJ - Get Report) , which manufactures acetaminophen medication Tylenol; Bayer AG (BAYZF) , which owns Alka Seltzer; and GlaxoSmithKline PLC  (GSK - Get Report) , which manufactures TheraFlu.

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