Why Is Antigenic Shift Dangerous?

As a result, a person becomes susceptible to flu infection again, as antigenic drift has changed the virus' antigenic properties enough that a person's existing antibodies won't recognize and neutralize the newer flu viruses. Antigenic drift is an important reason why people can get flu more than one time.

How does antigenic shift cause pandemics?

Antigenic shift refers to the complete replacement of the HA or NA with a novel HA or NA. These viruses are “new” viruses to which the population has no specific immunity. When such a new virus is introduced into a population, a severe, worldwide epidemic, or pandemic, of influenza can result.

Is antigenic shift or drift more dangerous?

Because the genes in the resulting virus are dramatically different, this is called antigenic shift. Antigenic shift is more concerning than antigenic drift. Antigenic shift can produce a version of influenza virus that no person's immune system has antibodies to protect against.