During the specified study period, we were able to identify certain newly emerging rotavirus genotypes introduced to Saudi Arabia, such as the uncommon G1P [4] and G12P [6] genotypes. Notably, there are at least 37 P types (P [1]-P [37]) and 27 G types (G1-G27) [
10,
11]. The common human RV-A genotypes that are circulating worldwide include: G1P [8], G2P [4], G3P [8], G4P [8] and G9P [8]. Globally, more than 90% of human RV-A cases have been attributed to G1P [8], G2P [4], G3P [8], and G4P [8] rotavirus genotypes. In Saudi Arabia, overall, rotavirus infection has a high prevalence (average: 33.7%) [
18]. Globally and particularly in the northern hemisphere countries, human RV-A infections occur in clusters in the winter months. In the Middle East and the gulf region several countries reported rotavirus seasonal peak between November and April including Oman, Iran, Tunisia, Morocco and Turkey [
19]. While others, Egypt and United Arab Emirates, recorded seasonal peak during July as well [
20]. In our country, however, the season of human RV-A infections starts with steadily increasing numbers of cases in July and the incidence of the disease spikes up during chilly winter months. Rotavirus infection cases seem to have increased steadily in the region and the highest numbers were observed in 2012 as compared to the previous years (Balkhy et al. Manuscript in preparation). This consistent increase in the numbers of human RV-A infections can possibly be attributed to the absence of national RV vaccination program in this country. Children less than 2 years of age were the most vulnerable to human RV-A infections. Previously, Kheyami et al. showed that 89% of rotavirus strains were of G1P8 genotype [
7,
21-
23]. Here, we found a consistent increase in the incidence of human RV-A infections during 2012 (30.6%) and the most prevalent genotypes were G1P [8] (61.5%) and G9P [8] (16.8%). We speculate that the emergence of the uncommon genotypes (≈5%), such as G1P [4] and G12P [6], could be due to either the expression of the natural variation of distinct human RV-A genotypes over time in rotavirus-infected Saudi children or they were circulating without detection. The phylogenetic analysis showed that G1P [4] and G12P [6], isolates from Riyadh, Saudi Arabia clustered with isolates from other countries such as Bangladesh, China, Japan, Thailand and Philippines. Nevertheless, it is possible that these genotypes were merging with the immigration of the foreign workers coming from Southeast Asia as the phylogenetic analysis has revealed. The divergent incidence of human RV-A infection and the fluctuating seasonal distribution of its genotypes underscore the need for a national RV vaccination program. As though the available vaccines do not cover all uncommon genotypes, however, their efficiency against various circulating human RV-A genotypes has been demonstrated in several studies [
24-
26]. Of note, rotavirus vaccines were recommended worldwide by the WHO in 2008; however, these have not been a part of routine Saudi vaccination program until 2013.