Still haven’t gotten your annual flu shot? “It’s not too late to get one, especially because this year’s flu got a late start in our hemisphere,” says Marvin M. Lipman, M.D., Consumer Reports' chief medical adviser. And getting a flu shot now is a very good idea: This year’s flu is so severe that the Centers for Disease Control and Prevention (CDC) has issued a severe flu warning advising doctors to encourage all patients who have not yet received the flu shot to get vaccinated ASAP.

A full-blown case of the flu can put you in bed for a week or two with symptoms including fever, chills, a sore throat or stuffy nose, body aches, and fatigue. On average of 5 to 20 percent of Americans get the flu every year, more than 200,000 are hospitalized, and thousands die. It poses special risks to the very old and the very young. 

But there is good news: So far the strains of the virus that are circulating are the same strains as this year’s flu shot targets. “If you’ve had the shot you may still get the flu, but there’s a good chance it will be a lot less severe,” Lipman says. 

So what should you do if, despite getting vaccinated, you come down with symptoms? If you're in a high-risk group, ask your doctor for antiviral drugs, says William Schaffner, M.D., an authority on infectious diseases and chairman of the preventive medicine department at Vanderbilt University School of Medicine in Nashville, Tenn.

Research suggests that the drugs osel­tam­ivir (Tamiflu) and zanamivir (Relenza) can ease flu symptoms, reduce complications, such as pneumonia, and reduce your chance of spreading the disease—if you start taking one within 48 hours of getting sick. You’re at high risk if you are 65 or older or younger than age 5, are pregnant or delivered a baby within the last two weeks, have a chronic disease such as asthma, diabetes, or heart, lung, or kidney disease, have a weakened immune system, are obese, or live in a nursing home or other chronic-care center. 

"The flu can make you really sick," Schaffner says, "If you wait three days to call the doctor for antiviral drugs, it could be too late." If you're in a high-risk group, one strategy he suggests is to ask your doctor for a prescription now so that it's ready to be filled in case you show flu symptoms. Don't wait for lab tests to come back, he says, since many are false negatives. 

A 2015 CDC study found that only about one in five high-risk patients got antiviral medication, which can lessen the severity of the symptoms by about a day and reduce the risk of complications, hospitalization, and death.

And if you're not in a high-risk group? The CDC says antiviral treatment also can be considered if your doctor thinks it's necessary and if the drugs can be taken within 48 hours of showing flu symptoms. But be aware that the cure can be as bad as the disease: Antivirals can cause nausea, vomiting, and increase the risk of headaches.

Your best bet against catching the flu this year is still the vaccine, Lipman says, along with frequent handwashing. If you do get sick, stay home to avoid spreading the illness.