While each serotype can cause the full spectrum of disease, virus strain is a risk factor.

Even if the virus strains are the same specific variety, the antigenicity is very different.

These are very similar, as they are made to match the specific virus strain.

Often, the degree of cross-immunity between virus strains is assumed to be related to their sequence distance.

When the capsid is broken down within a host, virus strains are released and begin reproduction.

Other experts are also concerned that the new virus strain could mutate over the coming months.

But, he added, there is no way to tell, by looking at the virus strain, whether it will be particularly virulent.

The pleconaril group had 21 virus strains, which remained susceptible.

Flu vaccines are prepared annually in anticipation of that year's virus strain.

These virus strains had undergone major genetic changes for which the population did not possess significant immunity.