Temporal and spatial fluctuations in the genotype distribution of human 
rotaviruses are continuously observed in surveillance studies. New genotypes, 
such as G9 and G12, have emerged and spread worldwide in a very short time span. 
In addition, reassortment events have the potential to contribute substantially 
to genetic diversity among human and animal rotaviruses. With the recent 
introduction of the two rotavirus vaccines, RotaTeq and Rotarix, in many 
countries, it appears that the total number of hospitalizations due to rotavirus 
infections is being reduced, at least in developed countries that implemented a 
universal immunization program. However, continued surveillance is warranted, 
especially regarding the long-term effects of the vaccines. No data analyses are 
available to clarify whether rotavirus vaccine introduction would allow other 
rotavirus P and G genotypes, which are not covered by the current vaccines, to 
emerge into the human population and fill the apparent gap. This kind of data 
analysis is essential, but its interpretation is hampered by natural and 
cyclical genotype fluctuations.