Rotavirus infection and intussusception: a view from retrospect

Evaluation of Adverse Reactions to Vaccines

The development and widespread use of vaccination over the past centuries has been the single most impactful intervention in public health, by effectively preventing morbidity and mortality from infectious diseases. Vaccination is generally well tolerated in the vast majority of the population, and the benefits of vaccination largely outweigh the risk of severe adverse events in the majority of patients. Vaccine hesitancy can be a significant concern and lead to infectious disease outbreaks. All health care providers play an important role in maintaining public confidence in vaccines because their attitude and knowledge is often critical in facilitating acceptance of a vaccine. The purpose of this review is to first, provide an understanding of the basic concepts that are relevant to vaccine pharmacovigilance, and secondly, to provide an overview and discuss management of both immune and nonimmune adverse events after vaccination.

Relationship between Pentavalent Rotavirus Vaccine and Intussusception: A Retrospective Study at a Single Center in Korea

PURPOSE

Despite withdrawal of RotaShield® and the development of second generation live attenuated rotavirus vaccines, concerns remain regarding the relationship between rotavirus vaccine and intussusception. Nevertheless, since there is no study in Korea, we reviewed data from cases at Severance Children's Hospital to determine the association between rotavirus vaccine and intussusception.

MATERIALS AND METHODS

Patients coded as intussusception and following a prescription of RotaTeq® from 2007 to 2013 were reviewed. We calculated comparative incidence figures (CIFs) and 95% confidence intervals (CIs) to compare the risk of intussusception in Korea with the risk in the United States. Expected cases within the four-week post-vaccination window were calculated by applying rates of intussusception from data compiled by the Health Insurance Review and Assessment Service (for a five-year period) to numbers of vaccinations.

RESULTS

In total, 10530 doses of pentavalent rotavirus vaccine were administered. A total of 65 intussusception cases were diagnosed, although only two cases occurred within four weeks after vaccination. This was compared to six cases within 999123 doses in United States from April 2008 to March 2013 (CIF, 31.63; CI, 31.33-31.93). When we adjusted incidence rate differences for both countries, the CIF decreased to 7.05 (CI, 6.72-7.40). When we compared our identified cases with the expected cases from our hospital, there was no increased intussusception occurring within four weeks of vaccination.

CONCLUSION

We found no association between pentavalent rotavirus vaccine and intussusception. Therefore, rotavirus vaccination should be considered due to its benefits of preventing rotavirus-associated diseases.

A critical time for rotavirus vaccines: a review

Universal introduction of rotavirus vaccines into childhood immunization programs is expected to substantially reduce the mortality from rotavirus gastroenteritis in developing countries (currently estimated at 702,000 annual deaths among children less than 5 years of age). In addition, it is expected to virtually eliminate hospitalizations due to rotavirus gastroenteritis in developed countries. Two rotavirus vaccines, Rotarix (GlaxoSmithKline Biologicals, Belgium) and RotaTeq (Merck & Co., USA) have recently completed Phase III clinical trials, each involving more than 60,000 children. Both vaccines appear safe with respect to intussusception, and are highly efficacious in preventing severe gastroenteritis due to rotavirus strains carrying predominantly serotype G1. The monovalent human rotavirus vaccine Rotarix, possessing serotype P1A[8],G1, is being first introduced into developing countries, whereas the pentavalent bovine-human reassortant rotavirus vaccine RotaTeq, comprising G-types G1, G2, G3, G4 and P-type P1A[8], will be initially introduced into the USA and Europe. Current disease burden estimates and economic justification will be required wherever the vaccines are introduced. Confirmation of the safety of both vaccines will require extensive postlicensure evaluation in which it will be key to assure adherence to administration of the first dose of either vaccine before 3 months of age. Assessment of the ability of each vaccine to provide protection against an increasingly diverse population of rotavirus strains will crucially depend on continuous global strain surveillance. Finally, efforts to improve existing rotavirus vaccines and to develop alternative vaccines should continue, so as to ensure that the prerotavirus vaccine era is consigned to a historical context.

A multi-country study of intussusception in children under 2 years of age in Latin America: analysis of prospective surveillance data

BACKGROUND

Intussusception (IS) is a form of acute intestinal obstruction that occurs mainly in infants and is usually of unknown cause. An association between IS and the first licensed rotavirus vaccine, a reassortant-tetravalent, rhesus-based rotavirus vaccine (RRV-TV), led to the withdrawal of the vaccine. New rotavirus vaccines have now been developed and extensively studied for their potential association with IS. This study aimed to describe the epidemiology and to estimate the incidence of IS in Latin American infants prior to new vaccine introduction.

METHODS

Children under 2 years of age representing potential IS cases were enrolled in 16 centers in 11 Latin American countries from January 2003 to May 2005. IS cases were classified as definite, probable, possible or suspected as stated on the Brighton Collaboration Working Group guidelines.

RESULTS

From 517 potential cases identified, 476 (92%) cases were classified as definite, 21 probable, 10 possible and 10 suspected for intussusception. Among the 476 definite IS cases, the median age at presentation was 6.4 months with 89% of cases aged <1 year. The male to female ratio was 1.5:1. The incidence of definite IS per 100,000 subject-years ranged from 1.9 in Brazil to 62.4 in Argentina for children <2 years of age, and from 3.8 in Brazil to 105.3 in Argentina for children aged <1 year. Median hospital stay was 4 days with a high prevalence of surgery as the primary treatment (65%). Most cases (88%) made a complete recovery, but 13 (3%) died. No clear seasonal pattern of IS cases emerged.

CONCLUSIONS

This study describes the epidemiology and estimates the incidence of IS in Latin American infants prior to the introduction of new rotavirus vaccines. The incidence of IS was found to vary between different countries, as observed in previous studies.

TRIAL REGISTRATION

Clinical study identifier 999910/204 (SERO-EPI-IS-204).

Rotarix in Japan: Expectations and Concerns

A live-attenuated, orally-administered, monovalent, human rotavirus vaccine, Rotarix® (GlaxoSmithKline Biologicals, Rixensart, Belgium), was licensed and launched in 2011 as the first rotavirus vaccine in Japan. The rotavirus causes a substantial disease burden with an estimated 790,000 outpatient visits, 27,000–78,000 hospitalizations, and approximately 10 deaths each year in Japan. Since a recent clinical trial showed that Rotarix was as efficacious in Japan as in other industrialized countries, it is expected that the annual number of rotavirus hospitalizations will be reduced to between 1000–3000, and that outpatient visits will be reduced to 200,000. The universal rotavirus immunization program with Rotarix was calculated to be at the threshold of being cost-effective, even from the healthcare perspective, and it was highly cost-effective from the societal perspective, assuming that Rotarix is co-administered with other childhood vaccines. While Rotarix contains only a single G1P[8] human rotavirus, the postlicensure studies in Brazil showed that Rotarix provided a 75%–85% protective efficacy against severe dehydrating diarrhea or hospitalizations due to fully-heterotypic G2P[4] strains. While postlicensure studies detected a small and finite risk of intussusception associated with the administration of Rotarix, the authors conclude that Rotarix is safe to administer to infants between 6-12 weeks of age for the first dose and by 24 weeks of age for the second dose. However, the authors strongly discourage the delayed administration of the first dose between 13-20 weeks of age, which is allowed without any warning. Given the high incidence of naturally-occurring intussusception in Japan (185 cases per 100,000 children/year among children less than 1 year of age), this should prevent pediatricians and parents from having ill-perceptions of Rotarix being associated with an increased number of temporally-associated intussusception, and fully appreciate the benefit of the rotavirus vaccine.

[Toward the elimination of rotavirus gastroenteritis by universal vaccination]

Rotavirus is the most important cause of severe gastroenteritis in children worldwide, and is most effectively controlled by vaccines. The Strategic Advisory Group of Experts (SAGE) of the World Health Organization (WHO) recommended, in 2009, the inclusion of rotavirus vaccination of infants into all national immunization programs. Two, live, orally-administrable vaccines are licensed globally. They are Rotarix, a G1P[8] monovalent, human rotavirus-based vaccine (GlaxoSmithKline), and RotaTeq, a pentavalent, bovine-human reassortant vaccine (Merck). Although the two vaccines are very different in antigenic composition and administration schedule, they are almost equally safe with respect to intussusception and 90-100% efficacious against severe rotavirus diarrhea. Countries where either vaccine was introduced into the national childhood immunization program have witnessed not only a drastic decrease in the number of rotavirus hospitalizations but a near 50% reduction in the number of all-cause-diarrhea hospitalizations. Rotavirus diarrhea, an emerging infectious disease because of its discovery in 1973, may now be among vaccine preventable diseases.

A critical review on a globally-licensed, live, orally-administrable, monovalent human rotavirus vaccine: Rotarix

Rotavirus is the major cause of severe gastroenteritis in children worldwide, and two, live, orally-administrable vaccines are licensed globally. They are Rotarix, a monovalent, human rotavirus-based vaccine (GlaxoSmithKline), and RotaTeq, a pentavalent, bovine-human reassortant vaccine (Merck). The RIX4414 strain, a G1P[8] virus, is contained in the Rotarix vaccine. It grows efficiently in the human intestine, as evidenced by vaccine virus shedding into faeces. Efficient multiplication of RIX4414 in the intestines may play a role in stimulating immune effectors other than neutralizing antibodies that may explain the protective immunity against fully heterotypic G2P[4] strains. The protective efficacy against severe rotavirus gastroenteritis afforded by Rotarix is consistently better against strains that share with RIX4414 both G and P serotypes (i.e., G1P[8]), or only P serotype (i.e., G3P[8], G4P[8] and G9P[8]). The Rotarix vaccine is safe regarding intussusception if its first dose is administered between 6 and 12 weeks of age and the last dose by 24 weeks of age with a minimum interval of 4 weeks between the two doses. The expansion by Advisory Committee on Immunization Practices, USA, of the age limit for the first dose to age <15 weeks, and the last dose by 8 months requires close monitoring.

Rotavirus infection and intussusception in Tunisian children: implications for use of attenuated rotavirus vaccines

BACKGROUND

A licensed rotavirus vaccine was withdrawn from use because of an increased risk of intussusception. The association of rotavirus vaccination with intussusception raised concerns about a potential link between natural rotavirus disease and intussusception. The objectives of the present study were to determine whether an epidemiological association with natural rotavirus infection existed.

METHODS

From 1984 to 2003, all children younger than 5 years with intussusception were retrospectively identified by medical charts, and from 1995 to 2003, a prospective surveillance study of rotavirus infection in children younger than 5 years was independently conducted. Epidemiological characteristics of intussusception and rotavirus infection were then compared.

RESULTS

A total of 533 cases of intussusception and 146 cases of rotavirus infection were identified. The incidence of intussusception for infants younger than 1 year was 62/100,000 child-years. The age distributions of intussusception and rotavirus gastroenteritis overlapped, and a masculine predominance was noted in both cases. No significant association was observed between the monthly distribution of intussusception and rotavirus infection.

CONCLUSION

The present study has not convincingly shown that rotavirus diarrhea plays a major role in intussusception. However, data about age and sex distributions supported the biologic plausibility of such an association.

Evaluation of recombinant BCG expressing rotavirus VP6 as an anti-rotavirus vaccine

Recombinant BCG expressing rotavirus VP6 was explored as an anti-rotavirus vaccine in a mouse model. Three promoters and five ribosome-binding sites were used in episomal and integrative E. coli-mycobacterium shuttle vectors to express VP6 in BCG. The VP6 gene was configured for accumulation within the BCG cytoplasm, secretion from the BCG cell or targeting to the BCG cell membrane. Vectors were assessed in terms of stability, levels of antigen production, immunogenicity and protection in mice. Gross instability occurred in episomal vectors utilizing the hsp60 promoter. However, three integrative vectors using the same expression system and two episomal vectors using inducible promoters were successfully recovered from BCG. Growth rates of the former were not detectably reduced. Growth rates of the latter were considerably reduced, implying the existence of a significant metabolic load. In the absence of selection, loss rate of these plasmids was high. VP6 production levels (0.04-1.78% of total cytoplasmic protein) were on the lower end of the range reported for other rBCG. One episomal and one integrated vaccine reduced viral shedding in intraperitoneally vaccinated mice challenged with rotavirus. Compared to controls, infection-associated faecal shedding of virus was reduced by 66% and 62%, respectively. These protective vectors differ in promoter, ribosome-binding site and antigen production level, but both link the VP6 protein to the 19kDa lipoprotein signal sequence, suggesting that transport of VP6 to the BCG membrane is important for induction of a protective immune response. Protection occurred in the absence of detectable anti-rotavirus antibody in serum or faeces, implicating cellular immunity in protection.

Rotavirus infection enhances lipopolysaccharide-induced intussusception in a mouse model

Unexpected reports of intussusception after vaccination with the live tetravalent rotavirus vaccine RotaShield resulted in voluntary withdrawal of the vaccine. Intussusception, a condition in which the intestine acutely invaginates upon itself, is the most common cause of intestinal obstruction in children. We report here the development of a mouse model to study rotavirus-induced intussusception. In this model, both homologous murine and heterologous simian rotavirus strains significantly enhanced the rate of lipopolysaccharide (LPS)-induced intussusception, and this enhancement was replication dependent, requiring rotavirus doses of greater than one 50% infectious dose. Rotavirus-induced intussusceptions did not have observable lymphoid lead points, despite the induction of intestinal lymphoid hyperplasia after rotavirus infection. Intussusceptions are also postulated to result from altered intestinal motility, but rotavirus infection had no effect on gastrointestinal transit. LPS-induced intussusception is associated with the induction of inflammatory mediators, and intussusception rates can be modified by inflammatory antagonists. We show that rotavirus infection significantly enhanced serum tumor necrosis factor alpha and gamma interferon cytokine levels after LPS treatment compared to uninfected mice. Together, these data suggest that rotavirus infection sensitized mice to the inflammatory effects of subsequent LPS treatment to enhance intussusception rates.

A high incidence of intussusception in Japan as studied in a sentinel hospital over a 25-year period (1978-2002)

The development of second-generation rotavirus vaccines requires knowledge of baseline incidence rates for intussusception in infants prior to vaccine introduction. To obtain such estimates we reviewed clinical records in a hospital that served as the major provider of paediatric beds in a local community in the northern part of Japan. During the 25-year period (1978-2002), there were 91 hospitalizations due to radiologically confirmed intussusception in children <5 years of age, of which 45% were <1 year of age. Assuming that all children with intussusception in the area had been admitted to this hospital, there were an average of 185 and 78 hospitalizations per 100000 person-years for children <1 year old and 5 years old respectively. There was period-to-period variability with no long-term secular trend in the incidence of intussusception. The incidence rate in Japan was among the highest thus far reported, providing further evidence of geographic variability.

A Hexavalent Human Rotavirus–Bovine Rotavirus (UK) Reassortant Vaccine Designed for Use in Developing Countries and Delivered in a Schedule with the Potential to Eliminate the Risk of Intussusception

There is an urgent need for a rotavirus vaccine, because up to 592,000 infants and young children <5 years old die each year from rotavirus diarrhea, predominantly in the developing countries. We have developed a tetravalent human-bovine rotavirus (UK) reassortant vaccine with VP7 (G) specificity for serotypes 1, 2, 3, and 4, which has been shown to be safe, immunogenic, and effective in preventing severe rotavirus diarrhea. However, because of the emergence of VP7 (G) serotype 9 as an epidemiologically important serotype and the importance of VP7 (G) serotype 8 in focal areas, we are planning to add human-bovine (UK) reassortants with G8 and G9 specificity to the tetravalent vaccine, thereby formulating a "designed" hexavalent vaccine for universal use. In addition, we propose that the vaccine be administered orally in a 2-dose schedule, with the first dose given at 0-4 weeks of age and the second dose given at 4-8 weeks of age, when infants are relatively refractory to developing intussusception, thereby avoiding the age period when naturally occurring intussusception is most prevalent (i.e., ages 3-4 months through age 9 months). In this way, there may be the potential to eliminate or at least significantly decrease the risk of intussusception associated with rotavirus vaccination.

Natural rotavirus infection is not associated to intussusception in Mexican children

AIMS

To determine whether natural rotavirus infection or infection by another enteropathogen is associated to intussusception (IS); and to describe the seasonality of IS compared with severe diarrhea (SD) and rotavirus SD in Mexican children.

METHODS

A prospective, observational, multicenter and case-control study was conducted in Mexico City from December 1999 to February 2001. Cases were children younger than 1 year old hospitalized for IS; diagnosis was made by clinical features, radiologic and/or surgery findings. Controls were children younger than 1 year old hospitalized for another disease than a gastrointestinal illness (NGI). Cases and controls were paired by age and date of admission (+/-3 months; for both), in a 1:2 ratio. A surveillance of IS cases, SD and rotavirus SD episodes was conducted during the study period. Stool samples collected soon after IS resolution or at admission were tested for rotavirus, adenovirus, astrovirus, bacteria and parasites.

RESULTS

Thirty cases of IS and 60 controls with NGI were studied. Rotavirus was not detected in any case of IS. Adenovirus (17%) was the only enteropathogen detected in IS. Rotavirus (8%), adenovirus (2%), astrovirus (2%) and bacteria (2%) were detected in NGI. Rotavirus infection was not associated with IS (odds ratio, 0; 95% confidence interval, 0-2.9), whereas adenovirus infection was strongly associated as risk factor for IS (odds ratio undefined; P = 0.003), compared with NGI. Seasonal variation in admissions for IS was small, whereas admissions for SD and rotavirus SD showed a marked seasonal increase during fall-winter.

CONCLUSIONS

In Mexican children, rotavirus infection was not associated to IS; whereas a significant association was observed between adenovirus and IS. Also there was no increase in IS cases during the sharply defined fall-winter rotavirus outbreak. Observations from this controlled study suggest that natural rotavirus infection is not a risk factor for IS. This information may have implications for development of a safer and effective rotavirus vaccine.

Safety and immunogenicity of RIX4414 live attenuated human rotavirus vaccine in adults, toddlers and previously uninfected infants

A live attenuated human rotavirus (HRV) vaccine, strain RIX4414, was tested sequentially in adults, previously infected toddlers, and previously uninfected infants. A single dose was given to adults and toddlers and found well tolerated. Next, a dose ranging (three different viral concentrations) safety and immunogenicity study was conducted in rotavirus IgA antibody negative infants (N= 192), who received two doses of RIX4414 vaccine or placebo at 2 and 4 months of age. No side effects were seen after vaccination. Specifically, administration of RIX4414 vaccine was not temporally associated with fever, diarrhea, or increase in liver transaminases. Rotavirus IgA seroconversion ranged from 50 to 88% after one dose and from 73 to 96% after two doses, depending on vaccine titer. After the first dose, on days 7-9 post vaccination, between 38 and 60% of the infants shed the vaccine virus, whereas after the second dose only 0 to 13% of the vaccinees shed the vaccine virus. It is concluded that RIX4414 strain HRV vaccine is virtually non-reactogenic and, at high titer, highly immunogenic in susceptible infants.

Intussusception, rotavirus, and oral vaccines: summary of a workshop

Rotavirus gastroenteritis continues to cause substantial morbidity and mortality worldwide, despite widespread breastfeeding and use of oral rehydration therapy. This burden of disease indicates that an effective, safe rotavirus vaccine is needed, and in 1998 the first rhesus-human reassortant rotavirus tetravalent vaccine, Rotashield, was licensed in the United States. However, the recommendations for its use were withdrawn in 1999 because of the recognition of an uncommon but serious adverse event, intussusception. A workshop in September 2001 was held to review the subsequent developments and research regarding this association, the proceedings of which are summarized here. Although the pathogenesis of this association remains unknown, epidemiologic evidence supports a causal relationship, with a population attributable risk of approximately 1 per 10 000 (range of 1 in 5000 to 1 in 12 000) vaccine recipients. Whether this association will exist with other candidate rotavirus vaccine strains and whether the attributable risk for intussusception would be similar in other populations administered this vaccine are unclear. Because perceptions of vaccine safety derive from the relative disease burdens of the illness prevented and adverse events induced, the acceptance of rare adverse events may vary substantially in different settings. Nevertheless, a continuing consensus on the need for a safe and effective vaccine to prevent rotavirus gastroenteritis, especially for use in developing countries, exists.

Rotavirus vaccines: development, current issues and future prospects

The potential benefit of safe and effective rotavirus vaccination in reducing morbidity and especially mortality from rotavirus gastroenteritis among children in developing countries has long been recognised. More recently, the focus of attention shifted to developed countries, where cost-effectiveness analyses justified the routine introduction of rotavirus vaccines into childhood immunisation schedules. The recent withdrawal in the U.S.A. of the first licensed rotavirus vaccine (the tetravalent rhesus reassortant rotavirus vaccine), following investigation into reports of intussusception among a number of vaccinees, has directed attention once more towards rotavirus vaccine use in developing countries. However, issues relating to vaccine safety, efficacy, and cost, remain to be overcome before widespread introduction of rotavirus vaccines can be anticipated.

Characterization of nontypeable rotavirus strains from the United States: identification of a new rotavirus reassortant (P2A[6],G12) and rare P3[9] strains related to bovine rotaviruses

Among 1316 rotavirus specimens collected during strain surveillance in the United States from 1996 to 1999, most strains (95%) belonged to the common types (G1 to G4 and G9), while 5% were mixed infections of common serotypes, rare strains, or not completely typeable. In this report, 2 rare (P[9],G3) and 2 partially typeable (P[6],G?; P[9],G?) strains from that study were further characterized. The P[6] strain was virtually indistinguishable by hybridization analysis in 10 of its 11 gene segments with recently isolated P2A[6],G9 strains (e.g., U.S.1205) from the United States, but had a distinct VP7 gene homologous (94.7% a.a. and 90.2% nt) to the cognate gene from P1B[4],G12 reference strain L26. Thus, this serotype P2A[6],G12 strain represents a previously unrecognized reassortant. Three P3[9] strains were homologous (97.8-98.2% aa) in the VP8 region of VP4 to the P3[9],G3 feline-like reference strain AU-1, but had a high level of genome homology to Italian bovine-like, P3[9],G3 and P3[9],G6 rotavirus strains. Two of the U.S. P3[9] strains were confirmed to be type G3 (97.2-98.2% VP7 aa homology with reference G3 strain AU-1), while the other was most similar to Italian bovine-like strain PA151 (P3[9],G6), sharing 99.0% a.a. homology in VP7. Cross-neutralization studies confirmed all serotype assignments and represented the first detection of these rotavirus serotypes in the United States. The NSP4 genes of all U.S. P3[9] strains and rotavirus PA151 were most closely related to the bovine and equine branch within the DS-1 lineage, consistent with an animal origin. These results demonstrate that rare strains with P and G serotypes distinct from those of experimental rotavirus vaccines circulate in the United States, making it important to understand whether current vaccine candidates protect against these strains.

Small bowel infections

Infections of the human gastrointestinal tract with enteric pathogens are among the leading causes of disease, suffering, and death worldwide. Enteric pathogens are ingested from contaminated food and water and pass through the entire gastrointestinal tract during establishment in the host and subsequent shedding and spread to new hosts. Nonetheless, each pathogen exploits a unique niche within the intestinal tract and has developed unique strategies to interact with different host cells and functions. The most important and prevalent infections of the small intestine are caused by diarrheagenic Escherichia coli, particularly enterotoxigenic and enteropathogenic E. coli, rotavirus, Giardia lamblia, and Cryptosporidium parvum. This review focuses on recent insights into the pathogenesis of infections with these pathogens and host defenses against them.

Protective efficacy of a sulfated sialyl lipid (NMSO3) against human rotavirus-induced diarrhea in a mouse model

Antiviral activity of sulfated sialyl lipid (NMSO3) against human rotavirus (RV) was examined in vitro and in vivo. NMSO3 inhibited the replication of four major serotypes (G1 to G4) of human rotavirus with a low 50% effective concentration of 1 to 5 microg/ml and 50% cytotoxic concentration of 153 microg/ml when determined by plaque assays with MA104 cells. Exposure of NMSO3 to HCl (pH 2.0) for 30 min exhibited no loss of anti-RV activity. Time-of-addition experiments revealed that NMSO3 inhibited the adsorption of four serotypes of RV to MA104 cells. Furthermore, an assay of virus binding with radiolabeled RVs revealed that NMSO3 inhibited the binding of virus to MA104 cells, suggesting that NMSO3 may bind to VP4 and/or VP7. Prophylactic oral administration of NMSO3 (10 microg three times per day, 4 days) to five suckling mice starting 30 min before inoculation of MO strain (3 x 10(6) PFU/mouse) prevented the development of diarrhea. Four of five mice showed no stool or brown formed stool, and only one mouse showed brown soft stool, while water treatment caused watery diarrhea in all five mice. The mean titer of antibody to RV in mice which received NMSO3 at 10 microg three times per day for 4 days was significantly lower than that of untreated, infected mice. NMSO3 is a promising candidate for the prophylactic treatment of human RVs.

Effect of rotavirus vaccination programme on trends in admission of infants to hospital for intussusception

BACKGROUND

Studies have reported a temporal association between a first dose of rotavirus vaccine (Rotashield) and infant intussusception. We investigated the effect of Rotashield vaccination use on intussusception admissions in ten US states.

METHODS

We analysed electronic databases containing 100% hospital discharge records for 1993-99 from ten US states, where an estimated 28% of the birth cohort had received Rotashield (based on manufacturer's net sales data). We examined records of infants admitted to hospital (<365 days old) with any mention of intussusception (International Classification of Diseases, ninth revision, clinical modification code 560.0). Excess admissions for intussusception during the period of Rotashield availability (October 1998 to June 1999) were estimated by direct comparison with the corresponding period of October 1997 to June 1998 (before Rotashield was available) and with adjustment for secular trends during 1993-98 by Poisson regression.

FINDINGS

Hospital admission for intussusception among infants younger than 365 days of age during the Rotashield period compared with previously was 4% lower (10 cases) by direct comparison and 10% lower (27 cases) by trend comparison, corresponding to a negative population attributable risk. Among infants aged 45-210 days (target age range for a first Rotashield dose), we estimated an increase in intussusception admissions of 1% (one excess admission) by direct comparison and 4% (4.6 excess admissions) by trend comparison, corresponding to a population attributable risk range of one excess admission in 66000-302000.

INTERPRETATION

We found no evidence of increased infant intussusception admissions during the period of Rotashield availability. The total intussusception admission risk attributable to Rotashield was substantially lower than previous estimates based on studies focusing on the immediate postvaccination weeks.