It's especially important that the elderly, nursing homes residents and people with chronic respiratory conditions such as asthma get a flu shot. He said the vaccine takes about two weeks to be effective. Last season most of the influenza cases in Texas occurred in January and February. Symptoms of influenza include sudden onset of fever, headache, chills, muscle aches, sore throat, nasal congestion, dry cough and extreme fatigue. Symptoms usually last one to two weeks.
Influenza can lead to pneumonia which can be fatal.