<p>The WHO warned countries in the Northern Hemisphere to be prepared to fight flu viruses H1N1, H3N2 and the B/Victoria lineage</p>
Influenza viruses are a group of RNA viruses that cause influenza, a contagious respiratory illness. They are classified into different types, including A, B, C, and D, with type A being the most common and responsible for seasonal epidemics and pandemics.
Vaccination strategies are public health approaches aimed at preventing infectious diseases through immunization. They involve the development and distribution of vaccines to protect populations from specific pathogens, such as influenza viruses.