Flu I.Q.: How to know when you have it and what to do

Half of the states in the nation are reporting widespread flu activity and the numbers are expected to rise. One hospital in San Jose, Calif. set up a large tent next to the emergency room, to deal with the overflow of patients.

Most people are suffering from the H1N1 virus, which is the most prevalent strain of the flu this year, and now, one of the top treatments made for children, Tamiflu, is in short supply.

CBS News medical contributor Dr. David Agus told the “CBS This Morning” co-hosts that currently 45 states are “rampant” with flu, but he said hopefully it will not be as bad as last year, where there were up to 40,000 deaths from the disease.

(Editor's note: New flu surveillance statistics released Friday afternoon show flu activity is widespread in 35 states, and cases of disease have been reported in all 50 states).

“It’s not too late for a flu shot,” said Agus. “It takes about 10 to 14 days for a flu shot to kick in and give you immunity … whether it’s your doctor or your pharmacist – get that flu shot, get prepared and be aware of the symptoms.”

Agus said that since the flu season could go as late as May, it’s definitely not too late to get a flu shot to prevent illness. The Centers for Disease Control estimates that only 40 percent of Americans have been vaccinated so far this season.

Also, Agus explained how the shortage of children’s liquid Tamiflu will impact consumers and how it might not be that big of a problem. Tamiflu is a drug that treats flu and prevents more serious complications.

“You would imagine that pharmaceutical companies know a big season’s coming -- let’s get lots of it on board -- but it’s still a business and they don’t keep as much on board as we need,” he said. “This year already we’re in short supply.”

However, if there is a shortage of Tamiflu in your area, Agus said physicians can take adult capsules and grind them down into smaller doses and mix them with a flavored liquid to give to younger patients.

Agus also said that the way to tell the difference between the flu, a common cold or a stomach virus, is that the flu typically does not have gastrointestinal or respiratory symptoms to start. Yet, he said they can imitate each other.

“The flu classically starts with fever and chills, and then if you have it for more than three days, you have to go to your doctor,” said Agus. “If you have it for more than three days, you can get a bacterial infection, or it could be something serious, so go to your doctor.”

Getting the flu isn’t just a problem because you’re sick for a few days, but it actually can cause other long-term health woes, Agus said.

“This what people don’t always understand, you will survive the flu – most people – again, tens of thousands of people die – but the inflammation from the flu can yield heart disease, cancer and brain diseases, a decade from now," he said. "So, we really have to pay attention and try to prevent it. It is a major problem.”

To watch the full interview with Dr. David Agus, watch the video in the player above.