Influenza vaccines may not prevent time off from influenza in healthy adults

Clinical question: 
Do vaccines prevent influenza in healthy adults?
Bottom line: 
There is insufficient evidence to decide whether routine vaccination to prevent influenza in healthy adults is effective. Influenza vaccination did not affect the number of people needing to go to hospital or to take time off work (the follow up period was up to 3 months post vaccine).
Caveat: 
Vaccination against influenza avoided 80% of cases at best (in those confirmed by laboratory tests, and using vaccines directed against circulating strains), but only 50% when the vaccine did not match, and 30% against influenza-like illness. Some vaccines cause pain and redness at the injection site (NNH* 1), muscle ache (NNH 27), and other very rare serious harms such as transient paralysis. *NNH = number needed to treat to cause harm in one individual.
Context: 
Influenza is a common disease which spreads easily and regularly develops new strains. Each year it affects 10–20% of the population. People considered at risk, (health professionals, those aged over 65, those with chronic respiratory disease, coronary artery disease, diabetes, chronic renal disease and cancer) are offered vaccination to prevent complications and as a public health measure in many countries.
Review CD#: 
CD001269
PEARLS No: 
50
Date: 
March, 2008
Authored by: 
Brian R McAvoy