Prevention of rotavirus disease: guidelines for use of rotavirus vaccine. American Academy of Pediatrics

Clinical evaluation of a single oral dose of human-bovine (UK) reassortant rotavirus vaccines Wa x UK (P1A[8],G6) and Wa x (DS-1 x UK) (P1A[8],G2)

The safety, infectivity, and immunogenicity of two human-bovine reassortant rotavirus candidate vaccines were evaluated in adults, children, and infants. One of these, Wa x UK, contained a single human rotavirus gene from the Wa strain that encoded VP4 P1A specificity in a background of 10 bovine genes including the VP7 gene that encodes G6 specificity, whereas the other, Wa x (DS-1 x UK), possessed the human rotavirus VP4 gene from the Wa strain as well as the human VP7 gene from strain DS-1 that encoded G2 specificity. Each of these vaccines appeared to be well-tolerated and immunogenic in infants less than 6 months of age following a single oral dose, and therefore should be evaluated further as vaccine candidates.

Detection of human group C rotaviruses in Nigeria and sequence analysis of their genes encoding VP4, VP6, and VP7 proteins

In a survey on the etiology of acute gastroenteritis in infants and young children in Nigeria, group C human rotaviruses were detected in two of 112 rotavirus positive stool specimens collected between 1999 and 2000. The VP7, VP6, and VP4 genes of the two Nigerian human group C rotavirus strains (Jajeri and Moduganari) were sequenced in this study. Comparative sequence analysis with other published human group C rotaviruses showed that the genes encoding the three structural proteins were remarkably conserved in primary structure with few mutations. The VP4 and VP7 genes from the two Nigerian strains were related more closely to each other than to those of other published strains, and formed a separate cluster on the phylogenetic tree. In contrast, it was of note that VP6 gene of strain Moduganari was related more closely to the Brazilian strain Belem than to the other Nigerian strain Jajeri. This is the first report of identification of human group C rotavirus in Nigeria and constitutes the first sequence data of human group C rotaviruses in the African continent.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

Viral causes of diarrhea

Viruses are important causes of diarrhea. In healthy adults, the main clinical manifestation is acute, self-limited gastroenteritis. Advances in molecular diagnostics have shown that epidemics of acute gastroenteritis most frequently are due to caliciviruses spread through contaminated food or through person-to-person contact. Application of similar technology is needed to make a definitive statement about the role of such candidate viruses as rotavirus, astrovirus, and adenovirus as the cause of nonepidemic acute gastroenteritis in adults. Rarely a previously healthy adult gets acute CMV colitis. CMV and EBV mainly cause diarrhea in immunocompromised patients, however. Advances in prophylaxis and treatment have reduced the frequency and severity of these diseases. Acute infantile gastroenteritis is caused by rotavirus, calcivirus, astrovirus, and adenovirus. These viral diseases of the gut are seen by the physician as routine and rare clinical problems.

Intussusception, rotavirus diarrhea, and rotavirus vaccine use among children in New York state

OBJECTIVE

To describe epidemiologic features of intussusception and rotavirus diarrhea in New York, to examine the baseline incidence and trends over time, and to ascertain whether an excess of cases occurred in the 9 months of vaccination with the newly licensed rotavirus vaccine.

METHODS

Hospital discharge data from 1989 through 1998 were reviewed for children (<1 year old) whose primary or secondary diagnosis was coded as intussusception or rotavirus diarrhea. Characteristics of patients admitted for intussusception and rotavirus diarrhea were compared, and trends over time were examined. For a subset of patients, medical records and vaccine histories for intussusception hospitalizations from October 1998 through June 1999 were analyzed. The number of intussusception cases attributable to rotavirus vaccine was calculated based on the penetration of the vaccine (21%) and a range of excess risks of intussusception among vaccinated children as estimated by the National Immunization Program (NIP).

RESULTS

From 1989 through 1998, 1450 intussusception-associated hospitalizations were reported in children <1 year old (average annual incidence 5.4/10 000). Among these children, 47% were treated medically and 53% had surgery, with 9% needing surgical resection. The incidence of intussusception declined over time from 6.1 per 10 000 in 1989 to 3.9 per 10 000 in 1998. Intussusception hospitalizations occurred throughout the year, whereas rotavirus-associated hospitalizations peaked from February to April. Of 20 patients with intussusception whose hospitalization charts were reviewed, 5 had received rotavirus vaccine. All 5 were hospitalized after their first dose of vaccine, were admitted before 7 months of age, were white, and had private insurance. A total of 81 cases of intussusception occurred during the 9-month period of rotavirus vaccination, compared with 78 during the same period in the prevaccination year. The number of excess intussusception cases observed (n = 3) was lower than expected using the NIP estimate of excess risk (1.8) among rotavirus vaccinated children (n = 12) but not significantly different from the risks identified in the NIP cohort studies (1 in 12 000).

CONCLUSION

Our data suggest that in New York the rate of intussusception has declined, and approximately 1 child in 2600 develops intussusception before 1 year of age. The different seasonality between intussusception and rotavirus-related hospitalizations suggests that if any causal association exists, it must be small. Unlike other studies, analysis of New York hospitalized discharge data failed to show an appreciable increase in the incidence of intussusception after introduction of the rotavirus vaccine.

Intussusception among recipients of rotavirus vaccine: reports to the vaccine adverse event reporting system

BACKGROUND

Rotavirus vaccine was licensed on August 31, 1998, and subsequently recommended for routine use among infants. To assess rare adverse events, postlicensure surveillance was conducted.

OBJECTIVE

To describe the cases of intussusception among rotavirus vaccine recipients reported to the Vaccine Adverse Event Reporting System from October 1998 through December 1999.

SETTING AND PARTICIPANTS

Infants vaccinated with rotavirus vaccine in the United States.

OUTCOME MEASURES

Intussusception confirmed by radiology, surgery, or autopsy report with medical record documentation or confirmed by a primary health care provider.

RESULTS

There were 98 confirmed cases of intussusception after vaccination with rotavirus vaccine reported to the Vaccine Adverse Event Reporting System; 60 of these developed intussusception within 1 week after vaccination. Based on calculations using vaccine distribution data and intussusception incidence rates from 2 separate databases, an estimated 7 to 16 cases would have been expected to occur in the week after vaccination by chance alone.

CONCLUSION

Using a passive surveillance system for vaccine adverse events, we observed at least a fourfold increase over the expected number of intussusception cases occurring within 1 week of receipt of rotavirus vaccine. Other studies were initiated to further define the relationship between rotavirus vaccine and intussusception. In light of these and other data, the rotavirus vaccine manufacturer voluntarily removed its product from the market, and the recommendation for routine use of rotavirus vaccine among US infants has been withdrawn.

Population-based study of rotavirus vaccination and intussusception

BACKGROUND

During the first year that the rhesus rotavirus tetravalent vaccine (RRV-TV) was licensed, the Vaccine Adverse Event Reporting System received several reports of intussusception after vaccination. To evaluate the risk of intussusception, we conducted a retrospective cohort study in ten managed care organizations.

METHODS

Cases of intussusception were identified by searching electronic databases for diagnoses of intussusception (ICD-9 Code 560.0) in infants 1 to 11 months of age and confirmed by medical chart review. Vaccination and enrollment data were obtained from administrative databases. Incidence rate ratios (RR) of intussusception were computed by dividing incidence rates in prespecified risk intervals after vaccination by the background rate of intussusception and adjusted for age by Poisson regression. Cox proportional hazard regression was used to evaluate risk by vaccine dose.

RESULTS

Of 463,277 children 56,253 had been vaccinated with a total of 91 371 doses of RRV-TV. The incidence rate of intussusception was 25/100,000 person years among unexposed infants and 340/100,000 person years 3 to 7 days postvaccination. In the interval 3 to 7 days after vaccination, the age-adjusted RR was 16.0 (95% confidence interval, 5.5 to 46.7) for all doses combined and 30.4 (95% confidence interval, 8.8 to 104.9) after the first dose. RRs for the 8- to 14- and 15- to 21-day risk intervals were >1.0, but the confidence intervals substantially overlapped 1.0. The attributable risk was one case of intussusception per 11 073 children vaccinated.

CONCLUSIONS

RRV-TV is associated with an increased risk of intussusception. The risk is greatest 3 to 7 days after the first vaccination dose.

Adverse events and vaccination-the lack of power and predictability of infrequent events in pre-licensure study

The recent setback in the development of a safe and effective rotavirus vaccine illustrates an important problem regarding prelicensure testing and its ability to identify rare vaccine-related adverse effects. It is our contention that the possibility of a rare but serious vaccine adverse effect is difficult to detect in prelicensure testing. In this paper, we review the history regarding the testing and eventual studies that led to the permanent withdrawal of that vaccine. The post-licensure discovery of a serious adverse event associated with the rotavirus vaccine is not unique among vaccines, but represents a recurrent phenomenon that in fact is mathematically predictable. Prelicensure studies examine thousands of subjects and not hundreds of thousands. A sample size of 10,000 subjects may provide excellent estimates of efficacy, but cannot provide an adequate denominator to rule out rare adverse events. It lacks the power. Just as with the rotavirus vaccine, only after hundreds of thousands of doses of vaccines are distributed, will such rare events appear often enough to permit detection. For that reason, we must depend upon the modern post-licensure surveillance programs that we already have in place.

Rotavirus infection and intussusception: a view from retrospect

A live orally-administrable rhesus rotavirus (RRV) tetravalent (TV) vaccine, licensed in the U.S.A. and the European Union, was recalled from the market because it was suspected to increase the risk of intussusception during the week following immunization. In contrast, natural rotavirus infection is generally believed not to cause intussusception. Because my experience contributed to the first paper that linked intussusception with rotavirus infection, I have re-examined our own data published 22 years ago and other studies on this issue. I also made a case study of adenovirus and intussusception as a paradigm to establish an etiological association of viral infection and intussusception. My hypothesis postulated in this review is that natural infection of susceptible (or predisposed) infants with some rotavirus strains, probably serotype G3 rotaviruses, will result in an appreciable fraction of idiopathic intussusception. Thus, the number of rotavirus-induced intussusception cases may change reflecting the relative frequency of G3 strains, which I believe was much higher in the 70s than during the last two decades. The epidemiological data indicate that the RRV-TV vaccine triggers intussusception at a rate significantly higher than the background incidence rate following the week of vaccination, particularly after the first dose. In contrast, the data do not suggest that the cumulative incidence among the vaccine recipients increases accordingly, implicating that the risk of intussusception attributable to the RRV-TV vaccine may be minimal.

Rotavirus vaccine and intussusception. Where do we go from here?

Since the discovery of rotavirus in 1973, vaccine technology has moved from the use of monovalent attenuated animal rotavirus strains to the development of multivalent human-animal reassortment vaccines. The first licensed vaccine, a rhesus-human tetravalent vaccine, was licensed in 1998. This vaccine was withdrawn from the market a year later when it was noted that administration of vaccine was associated with an increased risk of intussusception. The future of rotavirus vaccine is dependent on the reasons for this association that have yet to be discovered.

Challenges and controversies in immunization safety

No vaccine is perfectly safe or effective. As diseases such as diphtheria and polio fade, vaccine safety concerns, especially alleged links between vaccinations and several chronic illnesses, have become increasingly prominent in the media and to the public. This article reviews the current scientific evidence on several recent vaccine safety controversies. It also provides information on how various safety research is conducted, some of the concurrent challenges, and finally, some guidance on communicating with patients on vaccine risks.

Intussusception among infants given an oral rotavirus vaccine

BACKGROUND

Intussusception is a form of intestinal obstruction in which a segment of the bowel prolapses into a more distal segment. Our investigation began on May 27, 1999, after nine cases of infants who had intussusception after receiving the tetravalent rhesus-human reassortant rotavirus vaccine (RRV-TV) were reported to the Vaccine Adverse Event Reporting System.

METHODS

In 19 states, we assessed the potential association between RRV-TV and intussusception among infants at least 1 but less than 12 months old. Infants hospitalized between November 1, 1998, and June 30, 1999, were identified by systematic reviews of medical and radiologic records. Each infant with intussusception was matched according to age with four healthy control infants who had been born at the same hospital as the infant with intussusception. Information on vaccinations was verified by the provider.

RESULTS

Data were analyzed for 429 infants with intussusception and 1763 matched controls in a case-control analysis as well as for 432 infants with intussusception in a case-series analysis. Seventy-four of the 429 infants with intussusception (17.2 percent) and 226 of the 1763 controls (12.8 percent) had received RRV-TV (P=0.02). An increased risk of intussusception 3 to 14 days after the first dose of RRV-TV was found in the case-control analysis (adjusted odds ratio, 21.7; 95 percent confidence interval, 9.6 to 48.9). In the case-series analysis, the incidence-rate ratio was 29.4 (95 percent confidence interval, 16.1 to 53.6) for days 3 through 14 after a first dose. There was also an increase in the risk of intussusception after the second dose of the vaccine, but it was smaller than the increase in risk after the first dose. Assuming full implementation of a national program of vaccination with RRV-TV, we estimated that 1 case of intussusception attributable to the vaccine would occur for every 4670 to 9474 infants vaccinated.

CONCLUSIONS

The strong association between vaccination with RRV-TV and intussusception among otherwise healthy infants supports the existence of a causal relation. Rotavirus vaccines with an improved safety profile are urgently needed.

Oral versus intravenous: rehydration preferences of pediatric emergency medicine fellowship directors

OBJECTIVE

The American Academy of Pediatrics (AAP) recommends oral rehydration therapy (ORT) for management of uncomplicated childhood gastroenteritis with mild-moderate dehydration. However, ORT is widely underused relative to their recommendations. We compared ORT use by directors of Pediatric Emergency Medicine (PEM) fellowship training programs with AAP recommendations, and sought to identify their barriers to ORT.

METHODS

Mail/fax survey of the directors of U.S. and Canadian PEM fellowship programs. The survey included 10 scenarios of mild or moderately dehydrated children with gastroenteritis, a personal innovativeness scale, self-assessment of ORT experience and knowledge, and open-ended questions regarding perceived barriers to ORT use.

RESULTS

60/67 (89.6%) PEM fellowship program directors responded. All reported experience with and knowledge about ORT. Only 10/58 (17.2%) believe ORT is usually better than intravenous (i.v.) rehydration in all 10 clinical scenarios, and only 4/58 (6.7%) usually use ORT in all 10 scenarios. 18/58 (31%) usually use ORT for all mildly but no moderately dehydrated children. ORT use did not correlate with personal innovativeness scores. Important barriers cited by respondents include additional time requirements for ORT relative to i.v. rehydration (76.7%) and expectation of i.v. rehydration by parents (41.7%) or primary care physicians (10%).

CONCLUSIONS

Relative to AAP recommendations, PEM fellowship directors underuse ORT, especially for moderately dehydrated children. Physician innovativeness does not influence ORT use. Further study of effectiveness, length of stay, staff requirements, and ORT acceptance in the emergency department setting, especially in children with moderate dehydration, may influence ORT use.

Bacterial, viral and parasitic enteric pathogens associated with acute diarrhea in hospitalized children from northern Jordan

To determine the etiology of acute diarrhea in Jordanian children under 5 years of age, we examined stool samples from 265 children admitted to the pediatric ward at Princess Rahma Hospital for Children, Irbid, Jordan, for parasites, rotavirus and enteric bacteria. Using both traditional and molecular diagnostic techniques, we detected enteropathogens in 66.4% of patients with diarrhea. A single enteric pathogen was detected in 50.9% of the children, and multiple pathogens were detected in 15.5%. The prevalence of enteropathogens identified was as follows: rotavirus (32.5%), enteropathogenic Escherichia coli (12.8%), enteroaggregative E. coli (10.2), enterotoxigenic E. coli (5.7%), Shigella spp. (4.9%), Entamoeba histolytica (4.9%), Salmonella spp. (4.5%), Campylobacter jejuni/coli (1.5%), Cryptosporidium spp. (1.5%), enteroinvasive E. coli (1.5%), eae-, Ehly-positive E. coli (0.8%), Giardia lamblia (0. 8%) and Yersinia enterocolitica (0.4%). No Vibrio cholerae, Shiga toxin-producing E. coli, microsporidia, adenovirus or small round virus were detected. Findings from this study demonstrate that rotavirus and several types of diarrheagenic E. coli, which are not screened for during routine examinations of stool samples in public health laboratories, were the most frequently detected enteropathogens in these children. Our findings highlight the value of using a combination of traditional and molecular techniques in the diagnosis of diarrheal disease in this population.

Immunization of pediatric solid organ transplant candidates and recipients

Organ transplantation has evolved from an experimental procedure to an accepted treatment for otherwise irreversible or congenital disorders. The immunosuppression necessary to prevent rejection enhances the severity of many infectious diseases and may potentially attenuate the response to vaccines designed to prevent disease. In spite of the frequency and severity of infectious diseases in organ transplant recipients, many children are not fully vaccinated before transplantation. The safety and efficacy of many of the currently available vaccines for solid organ transplant recipients have not been evaluated. We review the currently available data on immunization safety and efficacy, discuss experimental vaccines, and outline strategies to avoid vaccine-preventable diseases in pediatric organ transplant recipients.

New combination vaccines

Physicians can achieve full vaccination at each of the recommended visits by administering three or four injections, but for infants, four injections seem to be a maximum in light of the size of the infant thigh, which is the preferred injection site. Thus, physicians must make room for all of the new vaccines on the horizon. To accomplish that task, combinations will be necessary. Progress toward that goal is occurring.

Rotavirus disease and its prevention in infants and children

Rotavirus disease causes immense morbidity and mortality in developing countries. In the United States, mortality is very rare, but the health care and societal costs of rotavirus-related morbidity exceed one billion dollars annually A new vaccine that prevents the illness recently was marketed in the United States. Economic issues surround national recommendations for its use. Economic, safety, and effectiveness issues will be resolved only with surveillance systems that document the effectiveness of immunization programs and their cost-effectiveness.

Use of state hospital discharge data to assess the morbidity from rotavirus diarrhea and to monitor the impact of a rotavirus immunization program: A pilot study in Connecticut

OBJECTIVES

Now that rotavirus vaccines have been licensed and recommended for routine immunization of US infants, there is an urgent need for data to assess the morbidity from rotavirus diarrhea and to monitor the impact of a rotavirus immunization program. In a pilot study, we have assessed the usefulness of state hospital discharge data on diarrhea in children to provide this information by examining data from Connecticut.

DESIGN

Retrospective analysis of discharge records from acute care, nongovernmental hospitals in Connecticut. Patients. Children 1 month through 4 years of age with a diarrhea-associated diagnosis listed on the discharge record. Setting. Connecticut, 1987 through 1996.

RESULTS

During the 10-year study period, a total of 11 324 diarrhea-associated hospitalizations (49.4 hospitalizations per 10,000 children) were reported. Diarrhea-associated hospitalizations peaked during February through April, especially among children 4 to 35 months of age. The seasonality and age distribution of diarrhea-associated hospitalizations of presumed noninfectious and viral etiologies resembled those of rotavirus-associated hospitalizations. During 1993 to 1996, rotavirus was coded for 10.4% of diarrhea-associated hospitalizations increasing from 8.6% in 1993 to 14.7% in 1996. The unadjusted median cost of a diarrhea-associated hospitalization during 1987 to 1996 and 1993 to 1996 was $1,941 and $2,428, respectively.

CONCLUSIONS

Diarrhea causes substantial morbidity in children from Connecticut. The winter seasonal peak of diarrhea-associated hospitalizations in children 4 to 35 months of age coinciding with the peak of rotavirus-specific hospitalizations suggests that rotavirus is an important contributor to the overall morbidity. Although our findings suggest incomplete coding of rotavirus cases, state hospital discharge data should provide sensitive and timely information to monitor the impact of a rotavirus immunization program in Connecticut.

Viral infections of the gastrointestinal tract

Acute gastroenteritis is common in adults. It can occur in institutional epidemics or epidemics of food-borne illness; in these cases, caliciviruses are the major cause of the condition. When acute gastroenteritis occurs in nonepidemic form, its causes are less clear. It may be due to caliciviruses or to the less common serotypes of childhood gastroenteritis viruses, such as rotavirus, astrovirus, and adenovirus. The pathogenesis of acute viral gastroenteritis is not completely understood. Old evidence suggests that mild villus damage is responsible, but new evidence indicates that active secretion and motility disturbance may be involved in the production of symptoms. Five common viruses can remain latent in gastrointestinal tissues and produce disease many years after initial infection. Two major herpesviruses, cytomegalovirus and herpes simplex virus, cause ulcerative disease of the gastrointestinal tract. This disease occurs in healthy persons but is more common and more severe in immunocompromised patients. Three other viruses--Epstein-Barr virus, human papilloma virus, and human herpesvirus-8--are implicated in benign and malignant proliferative diseases of the gastrointestinal tract. Epstein-Barr virus has been associated with immunoproliferative disease after transplantation and may also cause small-bowel and colonic lymphoma in healthy adults. It causes most AIDS-related lymphomas. Human papillomaviruses cause anorectal condyloma and anal cancer. Human herpesvirus-8 causes gastrointestinal Kaposi sarcoma.

Immunizations for the immunocompromised child

Although immunocompromised children are unlikely to have optimal immune responses to vaccines, some will benefit from immunization. They should receive inactivated vaccines that are routinely recommended for immunocompetent children plus pneumococcal and influenza immunizations. Live viral and bacterial vaccines are contraindicated with the exception of MMR. It may be given to children infected with HIV who do not have severe immunosuppression. The timing of immunizations is generally the same for immunocompromised and normal children. However, the MMR schedule in children infected with HIV is accelerated, with 2 doses given 1 month apart. Susceptible children whose immunosuppression is related to a temporary condition should be vaccinated after immune dysfunction has resolved. The question of revacination for children infected with HIV who are receiving effective antiretroviral therapy is under investigation, but no specific recommendations are currently available.

Tetravalent rotavirus vaccine

OBJECTIVE

To review the clinical efficacy, safety, and pharmacoeconomic data about the use of rhesus-human reassortant rotavirus tetravalent vaccine (RRV-TV) in infants and children.

DATA SOURCES

A MEDLINE search (January 1990-December 1998) was conducted to identify all publications on the RRV-TV vaccine including pharmacology, clinical trials, adverse effects, and pharmacoeconomics in infants and children. Bibliographies of articles were also used.

STUDY SELECTION

All randomized and placebo-controlled clinical efficacy trials were reviewed. Additionally, pharmacoeconomic studies focusing on the potential impact on healthcare costs were chosen for review.

DATA SYNTHESIS

Rotavirus-induced gastroenteritis is a significant problem in developed and developing countries. Various forms of a rotavirus vaccine have been studied worldwide. The tetravalent vaccine appears to have similar efficacy in developed and developing countries. It seems to be most effective against the most severe forms of gastroenteritis, with an 80% overall efficacy rate. This vaccine is well tolerated; the most common adverse effect is fever after the first dose. Pharmacoeconomic studies indicate that although the vaccine may be only moderately effective against less severe gastroenteritis, over $1 billion annually could potentially be saved in the US with its universal use.

CONCLUSIONS

The new rotavirus vaccine is effective in preventing and reducing the incidence of rotavirus-induced gastroenteritis. The morbidity, mortality, and healthcare costs from this disease may be reduced if this vaccine is provided to children worldwide.

Evidence of high-frequency genomic reassortment of group A rotavirus strains in Bangladesh: emergence of type G9 in 1995

We characterized 1,534 rotavirus (RV) strains collected in Bangladesh from 1992 to 1997 to assess temporal changes in G type and to study the most common G and P types using reverse transcription-PCR, oligonucleotide probe hybridization, and monoclonal antibody-based enzyme immunoassay. Results from this study combined with our previous findings from 1987 to 1991 (F. Bingnan et al., J. Clin. Microbiol. 29:862-868, 1991, and L. E. Unicomb et al., Arch. Virol. 132:201-208, 1993) (n = 2,515 fecal specimens) demonstrated that the distribution of the four major G types varied from year to year, types G1 to G4 constituted 51% of all strains tested (n = 1,364), and type G4 was the most prevalent type (22%), followed by type G2 (17%). Of 351 strains tested for both G and P types, three globally common types, type P[8], G1, type P[4], G2, and type P[8], G4, comprised 45% (n = 159) of the strains, although eight other strains were circulating during the study period. Mixed G and/or P types were found in 23% (n = 79) of the samples tested. Type G9 RVs that were genotype P[6] and P[8] with both long and short electrophoretic patterns emerged in 1995. The finding of five different genotypes among G9 strains, of which three were frequently detected, suggests that they may have an unusual propensity for reassortment that exceeds that found among the common G types. We also detected antigenic changes in serotypes G2 and G4 over time, as indicated by the loss of reactivity with standard typing monoclonal antibodies. Our data suggest that a vaccine must provide protection against type G9 RVs as well as against the four major G types because G9 strains constituted 16% (n = 56) of the typeable RV strains and have predominated since 1996.