This can lead to an entirely new viral strain, capable of sustained human-to-human transmission.

The symptoms exhibited vary depending on the viral strain, host ecotype, and environmental conditions.

This co-infection provides an opportunity for mixing of the viral genes between existing strains, thereby producing a new viral strain.

Both forms work by exposing the body to the viral strains within the vaccine.

The segmented nature of the genome allows for the exchange of entire genes between different viral strains.