This vaccine was efficacious in preventing rotavirus gastroenteritis, decreasing severe disease and health care contacts. The risk of intussusception was similar in vaccine and placebo recipients. (ClinicalTrials.gov number, NCT00090233.)

In infants, natural rotavirus infection confers protection against subsequent infection. This protection increases with each new infection and reduces the severity of the diarrhea.

The International Committee on Taxonomy of Viruses (ICTV) has recently approved several proposals submitted by the present Caliciviridae Study Group. These proposals include the division of the family into 4 new genera designated Lagovirus, Vesivirus, "Norwalk-like viruses (NLVs), and "Sapporo-like viruses (SLVs); the latter 2 genera were assigned temporary names until acceptable names can be determined by the scientific community. The genera have been further divided into the following species: Feline calicivirus and Vesicular exanthema of swine virus (genus Vesivirus), Rabbit hemorrhagic disease virus and European brown hare syndrome virus (genus Lagovirus), Norwalk virus (genus NLV), and Sapporo virus (genus SLV). In addition, the ICTV approved a proposal to remove the hepatitis E virus from the Caliciviridae into an "unassigned classification status.

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We identified a Norwalk-like calicivirus (CV) whose genome likely was derived from naturally occurring recombination. This strain (Arg320) was detected by the EIA developed against recombinant Mexico virus (rMxV) capsids, but the viral RNA polymerase sequence was closer to Lordsdale virus, in a separate genetic cluster of Norwalk-like viruses. A 3.3 kb cDNA from the RNA polymerase region to the 3' end of the genome of Arg320 was cloned and sequenced. The sequence demonstrated that the capsid region of Arg320 shared 95% amino acid identity with MxV, but 68% identity with Lordsdale virus, while the RNA polymerase region shared 95% identity with Lordsdale virus, but 87% identity with MxV. Pair-wise sequence comparisons identified a potential recombination site at the polymerase/capsid junction. This is the first example of a naturally occurring recombinant in the CV family. Further studies to search for and characterize other strains may be necessary for understanding the genetic diversity of the family.

BackgroundAntigenemia is commonly detected in rotavirus-infected children. Although rotavirus RNA has been detected in serum, definitive proof of rotavirus viremia has not been shown. We aimed to analyze a defined patient population to determine if infectious virus could be detected in sera from children with rotavirus antigenemia.Methods and FindingsSerum samples obtained upon hospitalization from children with gastroenteritis (57 stool rotavirus-positive and 41 rotavirus-negative), children with diagnosed bronchiolitis of known (n = 58) or unknown (n = 17) viral etiology, children with noninfectious, nonchronic conditions (n = 17), and healthy adults (n = 28) were tested for rotavirus antigen by enzyme immunoassay (EIA). Results of serum antigen testing were assessed for association with clinical and immunological attributes of the children. Rotavirus antigenemia was detected in 90% (51/57) of children with rotavirus-positive stools, in 89% (8/9) of children without diarrhea but with rotavirus-positive stools, in 12% (2/17) of children with bronchiolitis of unknown etiology without gastroenteritis, and in 12% (5/41) of children with gastroenteritis but with rotavirus-negative stools. Antigenemia was not detected in sera from children with noninfectious nonchronic conditions, children with bronchiolitis of known etiology and no gastroenteritis, or healthy adults. Neither age nor timing of serum collection within eight days after onset of gastroenteritis significantly affected levels of antigenemia, and there was no correlation between antigenemia and viral genotype. However, there was a negative correlation between serum rotavirus antigen and acute rotavirus-specific serum IgA (r = −0.44, p = 0.025) and IgG (r = −0.40, p = 0.01) titers. We examined 11 antigen-positive and nine antigen-negative sera for infectious virus after three blind serial passages in HT-29 cells using immunofluorescence staining for rotavirus structural and nonstructural proteins. Infectious virus was detected in 11/11 (100%) sera from serum antigen-positive children and in two out of nine (22%) sera samples from antigen-negative children (p = 0.002).ConclusionsMost children infected with rotavirus are viremic. The presence of viremia is directly related to the detection of antigenemia and is independent of the presence of diarrhea. Antigenemia load is inversely related to the titer of antirotavirus antibody in the serum. The finding of infectious rotavirus in the blood suggests extraintestinal involvement in rotavirus pathogenesis; however, the impact of rotavirus viremia on clinical manifestations of infection is unknown.

To determine whether naturally acquired serum IgA and IgG antibodies were associated with protection against rotavirus infection and illness, a cohort of 200 Mexican infants was monitored weekly for rotavirus excretion and diarrhea from birth to age 2 years. Serum samples collected during the first week after birth and every 4 months were tested for anti-rotavirus IgA and IgG. Children with an IgA titer >1:800 had a lower risk of rotavirus infection (adjusted relative risk [aRR], 0.21; P<.001) and diarrhea (aRR, 0. 16; P=.01) and were protected completely against moderate-to-severe diarrhea. However, children with an IgG titer >1:6400 were protected against rotavirus infection (aRR, 0.51; P<.001) but not against rotavirus diarrhea. Protective antibody titers were achieved after 2 consecutive symptomatic or asymptomatic rotavirus infections. These findings indicate that serum anti-rotavirus antibody, especially IgA, was a marker of protection against rotavirus infection and moderate-to-severe diarrhea.