This article from the FDA compares broad U.S. recommendations on Covid vaccination with those from other countries and announces the adoption of an evidence-based approach to such recommendations.

In 1958, a new strain of influenza A with different HA and NA was identified and antigenic shift was discovered; the need for a trivalent vaccine was recognized.

Every now and then, the virus changes dramatically in a process called antigenic shift. When this occurs, people become even less immune, and the likelihood of disease spread dramatically increases.

Every now and then, the virus changes dramatically in a process called antigenic shift. When this occurs, people become even less immune, and the likelihood of disease spread dramatically increases.

Every now and then, the virus changes dramatically in a process called antigenic shift. When this occurs, people become even less immune, and the likelihood of disease spread dramatically increases.

In 1968, a shift once again caused a pandemic. In 1976 and 2009 , concerns that the virus had shifted led to [fears that a new pandemic loomed]. But Americans were lucky once again.

In 1968, a shift once again caused a pandemic. In 1976 and 2009 , concerns that the virus had shifted led to fears that a new pandemic loomed. But Americans were lucky once again.

Antigenic shift and Antigenic drift in viruses. Antigenic shift is a process where two or more different strains of a virus combine to create a new subtype of virus. Often, this new viral strain will ...

In 1958, a new strain of influenza A with different HA and NA was identified and antigenic shift was discovered; the need for a trivalent vaccine was recognized.

Antigenic shift is a more abrupt, significant genetic change that occurs when two different influenza viruses combine to create a novel strain. This is where COBRA comes in.