Influenza vaccine.

The influenza vaccine helps to protect against infection with the influenza virus. Influenza is an acute viral respiratory illness with abrupt onset and is spread primarily by respiratory droplets from person to person (mainly through inhalation of virus-containing droplets). Influenza is caused by a group of viruses of the Orthomyxoviridae family, which are separated into three strain types (A, B, and C) according to their nuclear material.