Major changes in these proteins are termed "antigenic shifts", and minor changes are termed "antigenic drifts
Serological analyses are, however, essential for epidemiological studies and monitoring antigenic drift
. A titer rise of hemagglutination inhibition (HI) antibodies, and in many cases also virus neutralization (VN) antibodies, are primary end points in clinical trials that assess the efficacy of the yearly updated whole inactivated vaccines (WIV), live attenuated vaccines (LAIV), and novel vaccination strategies.
These viruses are able to mutate and change very rapidly in a host due to their ability to undergo antigenic drift
and/or antigenic shift.
is a slight change in a particular subtype, but does not result in a new subtype.
This shape-shifting, called antigenic drift
, is why influenza vaccines a[euro]" which are designed to elicit antibodies matched to each year's circulating virus strains a[euro]" must be reformulated annually.
Annual human influenza epidemics occur because the influenza viruses change their antigenic structure ('antigenic drift
') to produce new strains that can cause infection in persons who have been previously infected or vaccinated with different strains.
This strategy, known as antigenic drift
, works well as a short-term survival tactic for the virus: the speed with which slight variations develop keeps populations susceptible to infection.
Frequent antigenic change, known as antigenic drift
, is caused by mutations during reproduction of the virus, and results in new variants of influenza.
No significant antigenic drift
of novel H1N1 virus away from what is in the vaccine has been encountered so far in the United States, he said.
* Antigenic drift
and shift as they relate to epidemics, pandemics and vaccine effectiveness.
But, even though we know which strains cause the flu and have a vaccine that prevents it, the vaccine must be reformulated every year because the strains regularly mutate through a gradual process called antigenic drift
. Scientists can usually stay ahead of the mutations and create a new vaccine each year to help prevent a flu caused by the strains that mutated gradually, but in rare cases when one of the type A strains mutates abruptly and unexpectedly in a process called antigenic shift, that year's vaccine can't prevent an outbreak.
First, it is very prone to antigenic drift
. This means that the antigenic markers on the outside of the organism change slightly from year to year, perhaps to help the virus survive.