Comparison of influenza viruses (a) Characteristic Influenza A Influenza B Genome Negative-strand RNA, Negative-strand RNA, eight segmented genes eight segmented genes Sequence High Moderate variability in HA and NA Mode of antigen Antigenic drift
and Antigenic drift
only variation antigenic shift Hosts Humans, avian, swine, Humans only equine, marine mammals Epidemiology Epidemic, pandemic Epidemic, nonpandemic (a) RNA, ribonucleic acid; HA, hemagglutinin; NA, neuraminadase.
Vaccines may be ineffective in the field due to the antigenic drift
caused by the observed rapid mutation rate of the influenza virus, according to these physicians.
Gradual changes in the age distribution of excess deaths in the years following the 1918 influenza pandemic in Copenhagen: using epidemiological evidence to detect antigenic drift
These epidemics caused unusually high illness and death in young children (33,34), consistent with the antigenic drift
away from both the 2007 Southern Hemisphere subtype H3N2 and H1N1 vaccine strains (33).
The genetic makeup of influenza viruses allows frequent minor genetic changes, known as antigenic drift
, and these changes require annual reformulation of influenza vaccines.
Mutations S123P and S129A, R to G substitution in the HA cleavage site, and S155N and K189N mutations at antigenic site B (which could explain the antigenic drift
measured) are characteristics that seem to have become established in the latest Cambodian isolates (online Appendix Table, available from www.
Protection Against Antigenic Drift
and Antigenic Shift
The antigenic homogeneity of the canine viruses suggests that measurable antigenic drift
has not yet occurred.
Additionally, major antigenic drift
among influenza viruses (H1N1 to H2N2 to H3N2 from 1918 to 1969) can be temporally mapped to above-ground nuclear testing in the flight paths of migratory birds across Siberia to Eastern China.
Monitoring the genetic structure of this virus is needed for predicting changes that may confer ability to cause pandemics: pathogenicity, host range, and antigenic drift
The difficulty of creating a diagnostic device for influenza is due to the antigenic drift
or mutation of the virus from year to year.
The immune responses elicited by subpotent vaccines may exert selection pressure that favors antigenic drift
and shift (Figure).
of H5N2 viruses belonging to the Mexico lineage, resulting in lower identity (less similarity) to the vaccine strain, has been described (16).
These findings support the notion that cats may be broadly susceptible to circulating H5N1 viruses and thus may play a role in reassortment, antigenic drift
, and transmission.
Every 2 to 5 years, the accumulation of mutations results in a major antigenic drift
away from the previously circulating strains (4).