In very rare cases when a person is allergic to the vaccine, there may be an immediate reaction. Other viruses, bacteria and food poisoning are much more common causes of nausea, vomiting and diarrhea. You can catch the flu from going outdoors in cold weather. Flu epidemics happen in the winter months because that's when the virus spreads across the country. It has nothing to do with being outside in cold weather.
Most people recover within one to two weeks.
But others, especially the elderly, may feel weak for a long time after flu symptoms go away. Treatment Four prescription medications are now available to treat flu. Two new drugs that may be used to treat influenza types A and B, but have not yet been approved for prevention, were approved by the U.S. Food and Drug Administration during 1999. All four of these prescription drugs are most effective when treatment starts within 48 hours after flu symptoms appear. After that, they are less likely to bring about a more rapid recovery.