Influenza FAQ

Influenza is caused by influenza viruses. Viruses are tiny microscopic organisms that spread through the air from the respiratory tract of an infected person when they talk, sneeze or cough. Viruses are easily spread between people through touch and/or respiratory droplets

No, flu vaccines cannot cause flu illness. Flu vaccines given with a needle (i.e., flu shots) are made with either inactivated (killed) viruses, or with only a single protein from the flu virus. The nasal spray vaccine contains live viruses that are attenuated (weakened) so that they will not cause illness.

Sudden onset of fever, aching muscles, sore throat, and non-productive cough. Additional symptoms could be runny nose, headache, burning sensation in the chest, eye pain and sensitivity to light. Older adults often do not experience fever.

The most frequent complications from influenza are viral and bacterial pneumonia. Other complications include inflammation of the heart, brain or muscles. Influenza can also worsen conditions such as asthma, congestive heart failure and diabetes.

A person may pass the virus from one day before symptoms start through 5 to 7 days after illness onset.

Influenza vaccine is given each year because immunity decreases after a year and because influenza vaccine viruses are updated almost every year. An annual vaccination is recommended even if the strains change little from one year to the next.

No. Neither the injectable or the nasal spray vaccine can cause influenza. Protective immunity develops about 2 weeks after vaccination. It is possible that a recently vaccinated person can be exposed to influenza disease before they develop immunity from the vaccine and consequently develop the disease. Influenza vaccine only protects against certain influenza viruses, not all viruses.