Question

Periodic revaccinations are necessary for protection against __________________virus because of constant _____________________________ of surface molecules .

Question 69 options:

	Influenza; antigenic drift
	Herpes; Inversion
	Polio; binding
	Papilloma; Loss
	None of the above

Answer 1

Ans.

• Infection caused by influenza virus in human population is often manifested in the form of seasonal epidemics.
• Understanding the short term evolution of influenza is necessary for several reasons in order to form a vaccine policy.
• In the analysis of short term evolution of influenza, observation should be made toward changes in the individual nucleotide in haemagglutinin of the virus and the time scale of the occurance of antigenic drift.
• Strain differences can be observed during a single season of epidemic.
• The reason of such variation in strains is usually unknown.
• A possible explanation of the said phenomenon may be a transient phase of antigenic drift.
• It may be difficult to detect antigenic drift because of the involvement of several other processes such as reassortment, purifying selection, selected mixing of hosts... etc.
• Antigenic drift can be defined as a genetic variation type in viruses which occurs because of the accumulation of mutations in the genes of virus coding for those surface proteins of virus that is recognized by the host antibodies.
• This may give rise to a new virus strain that may not be effectively prevented by the antibodies which inhibited infections of previous strains.
• So, Periodic revaccinations are necessary for protection against influenza virus because of constant antigenic drift of surface molecules.