Random mutations in the genes of a virus drives antigenic drift,^[1][2] a process that changes the antigens of the virus. As these changes accumulate it may help the virus to evade the immune system since antigens are what the immune system recognizes. Antigenic drift can lead to a loss of immunity or vaccine mismatch.

Contents 1 In influenza viruses 2 See also 3 Notes 4 Further reading 5 External links

[edit] In influenza viruses

In the influenza virus, the two relevant antigens are the surface proteins, hemagglutinin and neuraminidase^[3]. The hemagglutinin is responsible for entry into host epithelial cells while the neuraminidase is involved in the process of new virions budding out of host cells. The host immune response to viral infection is largely determined by the immune system's recognition of these influenza antigens. Vaccine mismatch is a potentially serious problem. Antigenic Drift is the continuous process of genetic and antigenic change among flu strains.

To meet the challenge of antigenic drift, vaccines that confer broad protection against heterovariant strains are needed against seasonal, epidemic and pandemic influenza.^[4].

As in all RNA viruses, mutations in influenza occur frequently because the virus' RNA polymerase has no proofreading mechanism, providing a strong source of mutations. Mutations in the surface proteins allow the virus to elude some host immunity, and the numbers and locations of these mutations that confer the greatest amount of immune escape has been an important topic of study for over a decade^[5][6][7].

Antigenic drift has been responsible for heavier-than-normal flu seasons in the past, like the outbreak of influenza H3N2 variant A/Fujian/411/2002 in the 2003 - 2004 flu season. All influenza viruses experience some form of antigenic drift, but it is most pronounced in the influenza A virus.

Antigenic drift should not be confused with antigenic shift, which refers to reassortment of the virus' gene segments. As well, it is different from random genetic drift, which is a important mechanism in population genetics.

[edit] See also

• Antigenic shift

[edit] Notes

[edit] Further reading

Boni MF. Vaccination and antigenic drift in influenza. Vaccine. 2008 Jul 18;26 Suppl 3:C8-14. Review. PMID: 18773534

Gog JR. The impact of evolutionary constraints on influenza dynamics. Vaccine. 2008 Jul 18;26 Suppl 3:C15-24. Review. PMID: 18773528

[edit] External links

• An illustration of antigenic drift
• A technical definition

v • d • e Topics in population genetics Key concepts Hardy-Weinberg law · Genetic linkage · Linkage disequilibrium · Fisher's fundamental theorem · Neutral theory · Price equation Selection Natural · Sexual · Artificial · Ecological Effects of selection on genomic variation Genetic hitchhiking · Background selection Genetic drift Small population size · Population bottleneck · Founder effect · Coalescence · Balding–Nichols model Founders R. A. Fisher · J. B. S. Haldane · Sewall Wright Related topics Evolution · Microevolution · Evolutionary game theory · Fitness landscape · Genetic genealogy List of evolutionary biology topics

v • d • e Microbiology: Virus Components Viral envelope · Capsid · Viral protein Viral life cycle Viral entry · Viral replication · Viral shedding · Virus latency Genetics Reassortment · Antigenic shift · Antigenic drift · Phenotype mixing Other Virus disease · Laboratory diagnosis of viral infections · Antiviral drug · Bacteriophage · Neurotropic virus · Oncovirus