Flu season could be bad this year, doctors say

Flu season is officially here and it could be a bad one, USA Today reported this week.

The official start of flu season begins when at least 2.2 percent of patients are reporting flu symptoms, a measurement tracked by the Centers for Disease Control and Prevention. The U.S. reached that level in late November, marking an early start to flu season.

Normally, flu season begins in mid- to late-December and peaks in January or February, Paul Sax, an infectious disease physician at Brigham and Women’s Hospital in Boston, told USA Today.

The CDC tracks flu outbreaks through a map that indicates flu activity in each state. At last count, the flu was widespread in Oklahoma, Louisiana, Massachusetts, and Georgia.

Why is this year expected to be bad?

It's difficult to say exactly how bad flu season might become, but one indicator in particular has health officials concerned.

Australia recently finished its flu season, and it was a rough one. Australia had 2.5 times the number of flu cases this year when compared to the previous year, according to U.S. News & World Report.

The concern is that the same kind of flu season could happen in the U.S.

"In general, we get in our season what the Southern Hemisphere got in the season immediately preceding us," Dr. Anthony Fauci, director of the United States' National Institute of Allergy and Infectious Diseases, told CNN.

Several different strains of the flu exist, and the one the most common in Australia was H3N2.

What about vaccines?

This year's flu vaccine will likely be about 10 percent effective, CBS News reported. The U.S. is using the same vaccine Australia used, which was about 10 percent effective in fighting the flu there. Typically, flu vaccines are about 42 percent effective in fighting off the illness. But flu shots can be anywhere from 10 percent to 60 percent effective.

The flu comes in may different strains and it's always changing, Dr. Pardis Sabeti, a Harvard professor and infectious disease expert, told CBS News.

"So by the time we pick a version of the virus to make into a vaccine and put it into production, it might take six to eight months and in that time the virus might change," Sabeti said.

As with any medication, there is a risk of having an adverse reaction. Common reactions are swelling from the shot, headache, fever, nausea or muscle aches.

The CDC reports that some people have developed Guillain-Barré syndrome, a rare immune system disorder, after taking certain injections — and that includes the flu vaccine. The risk is low, however, about one or two in a million for each flu shot administered, according to the CDC.

A study suggested that U.S. women who were pregnant and had miscarriages between 2010 to 2012 were likely to have taken "back-to-back annual flu shots" that protected against swine flu, The Associated Press reported.