PHOENIX (KSAZ / AP) - Health officials say flu cases are widespread in Arizona with more than 2,600 cases reported than this time last year.
The Arizona Department of Health Services say as of Wednesday, there have been almost 3,000 cases of flu reported compared to less than 350 for the same time period in 2016.
That's a 758 percent increase in flu activity.
Health officials say during the past two flu seasons, Arizona did not reach widespread activity until February.
But with the colder weather ready to kick in, health experts think it's about to get worse.
"We've definitely seen influenza hitting the valley very quickly and with a vengeance this year," said Dr. Janice Johnston, the Medical Director of Re-Direct Health.
Since the virus mutates so quickly, it's hard to keep up.
"Every year the vaccine manufacturers try to predict what type of virus is going to be coming to the country," Dr. Johnston said.
But every year, the numbers show that those manufacturers get it wrong.
Only once in the last five years has the vaccine proven to be more effective than not. And only one time in the last 13 years has the vaccine been at least 60 percent effective.
At the very least, doctors say if you're sick, stay home.
"A person who has the flu should stay home, don't go to work if you know that you have the flu, it's just going to spread it to others," Dr. Johnston said.