Major outbreaks happen?

Outbreak of influenza will occur when new strains of flu virus has occurred. Since a new virus strain itself. People are no immunity to it. Virus can spread and cause serious diseases to quickly.

New influenza virus strains. Often caused by mutations of viruses that cause disease in animals used in other species such as poultry or pig then. Mutations that. Is that it can contact to humans. If a virus fierce. Such as influenza virus, which can cause death to many birds. When it can mutate and contact from person to person has been. These viruses can cause fierce people dead not differ from all birds.