Lack of an apparent association between intussusception and wild or vaccine rotavirus infection

Exploring the Infectious Contribution to Intussusception Causality Using the Effects of COVID-19 Lockdowns in Australia: An Ecological Study

BACKGROUND

Intussusception is the primary cause of acute bowel obstruction in infants. The majority of cases <2 years of age are classed as idiopathic, with viral infection implicated as one of the causes. Coronavirus disease 2019 (COVID-19) public health measures led to significant decreases in communicable disease prevalence. During these times, reductions in intussusception frequency were greater than would be expected with our previous understanding of its infectious etiology.

METHODS

We conducted a retrospective, multistate, ecological study over a 12-year period. Monthly case numbers of "intussusception"-coded admissions (code K56.1; International Classification of Diseases and Related Health Problems, Tenth Revision, Australian Modification) were acquired from state-wide admissions data sets from New South Wales, Victoria, and Queensland, representing 77.62% of the eligible Australian population. These counts within differing jurisdictional lockdowns were compared with non-lockdown periods in order to investigate a correlation between intussusception frequency and lockdown periods.

RESULTS

We found a negative association between intussusception frequency and lockdown periods in both eligible states. The largest reductions were seen in the <2-year age groups, with Victoria experiencing a 62.7% reduction (rate ratio, 0.37; P < .001) and New South Wales a 40.1% reduction (0.599; P = .006) during lockdown times. Controls for variations in lockdown restrictions between both regional and metropolitan areas also showed expected decreases.

CONCLUSIONS

Our ecological study demonstrates significant decreases in the frequency of pediatric intussusception admissions during the COVID-19 lockdown periods. The unexpected magnitude of the reductions suggests that the true proportion of infectious disease-caused idiopathic intussusception is greatly underestimated.

Leveraging Beneficial Off-Target Effects of Live-Attenuated Rotavirus Vaccines

Following the introduction of live-attenuated rotavirus vaccines in many countries, a notable reduction in deaths and hospitalisations associated with diarrhoea in children <5 years of age has been reported. There is growing evidence to suggest that live-attenuated vaccines also provide protection against other infections beyond the vaccine-targeted pathogens. These so called off-target effects of vaccination have been associated with the tuberculosis vaccine Bacille Calmette Guérin (BCG), measles, oral polio and recently salmonella vaccines, and are thought to be mediated by modified innate and possibly adaptive immunity. Indeed, rotavirus vaccines have been reported to provide greater than expected reductions in acute gastroenteritis caused by other enteropathogens, that have mostly been attributed to herd protection and prior underestimation of rotavirus disease. Whether rotavirus vaccines also alter the immune system to reduce non targeted gastrointestinal infections has not been studied directly. Here we review the current understanding of the mechanisms underlying off-target effects of vaccines and propose a mechanism by which the live-attenuated neonatal rotavirus vaccine, RV3-BB, could promote protection beyond the targeted pathogen. Finally, we consider how vaccine developers may leverage these properties to improve health outcomes in children, particularly those in low-income countries where disease burden and mortality is disproportionately high relative to developed countries.

Novel vaccine safety issues and areas that would benefit from further research

Vaccine licensure requires a very high safety standard and vaccines routinely used are very safe. Vaccine safety monitoring prelicensure and postlicensure enables continual assessment to ensure the benefits outweigh the risks and, when safety problems arise, they are quickly identified, characterised and further problems prevented when possible. We review five vaccine safety case studies: (1) dengue vaccine and enhanced dengue disease, (2) pandemic influenza vaccine and narcolepsy, (3) rotavirus vaccine and intussusception, (4) human papillomavirus vaccine and postural orthostatic tachycardia syndrome and complex regional pain syndrome, and (5) RTS,S/adjuvant system 01 malaria vaccine and meningitis, cerebral malaria, female mortality and rebound severe malaria. These case studies were selected because they are recent and varied in the vaccine safety challenges they elucidate. Bringing these case studies together, we develop lessons learned that can be useful for addressing some of the potential safety issues that will inevitably arise with new vaccines.

Incidence of intussusception before and after the introduction of rotavirus vaccine in Korea

Background

Recent studies have reported that after the introduction of rotavirus vaccine the incidence of intussusception did not change among infants, or slightly increased at the age immediately after the first dose. The rotavirus vaccines were introduced in Korea for private market use in 2007–2008. We investigated the incidence of intussusception before (2002–2006) and after (2009–2015) the vaccine introduction in Korea.

Methods

We conducted an interrupted time series study that used data from the Korean National Health Insurance database to identify infants (<12 months of age) who were diagnosed with intussusception and underwent non-invasive or invasive reduction from 2002 to 2015. According to the recommended ages for immunization, the annual intussusception incidence and the incidence rate ratios were calculated among three age groups, 6–14, 15–24, and 25–34 weeks.

Results

The annual incidences in infants have decreased over time from 241.7 per 100,000 infants (pre-vaccine period) to 160.1–205.2 per 100,000 infants (post-vaccine period). The incidence rate ratio during the post-vaccine period ranged from 0.66 to 0.85. The incidences of intussusception in all three infant age groups have decreased in post-vaccine period compared to pre-vaccine period (incidence rate ratio range: 0.31–0.65, 0.47–0.75, and 0.68–0.94 in 6–14, 15–24, and 25–34 weeks, respectively).

Conclusions

The incidence of intussusception in infants did not increase after the rotavirus vaccine introduction in Korea, but rather decreased over the past decades. Since the incidence of intussusception varies according to country or region, continuous monitoring the incidence of intussusception in infants is necessary in each county or region.

Nationwide Population-Based Epidemiologic Study on Childhood Intussusception in South Korea: Emphasis on Treatment and Outcomes

PURPOSE

This was a nationwide population-based study conducted to investigate the epidemiology, treatment, disease outcomes, and associated factors of childhood intussusception in South Korea.

METHODS

Data from the Korean National Health Insurance Service database on all patients <18 years old diagnosed with intussusception from 2007 to 2017 were analyzed.

RESULTS

A total of 34,688 cases were identified among 30,444 patients. The overall incidence was 28.3/100,000 person-years with a male predominance. Most cases (83.1%) occurred in children <3 years old, with an annual incidence of 195.2, 200.1, and 118.6 cases per 100,000 children in their first, second, and third year of life, respectively. The median age at the first occurrence was 18.7 months, and it was higher in boys than in girls. The post-discharge recurrence rate was 10.6% (3,226/30,444) and the in-hospital recurrence rate was 6.1% (1,842/30,444). The total recurrence rate (post-discharge recurrence and/or in-hospital recurrence) was 15.0% (4,580/30,444). Enema reduction was successful in 90.0% of cases. Enema reduction was more successful in girls than in boys. A total of 3,296 (10.8%) patients underwent 3,481 surgeries, including 735 (21.1%) laparoscopic surgeries. Post-discharge recurrence and surgery were significantly affected by age, sex, and hospital type. Mortality was noted in nine cases (0.03%).

CONCLUSION

Our study provides accurate epidemiologic data on the treatment and outcomes of intussusception through complete enumeration during an 11-year-period.

Overview of the Development, Impacts, and Challenges of Live-Attenuated Oral Rotavirus Vaccines

Safety, efficacy, and cost-effectiveness are paramount to vaccine development. Following the isolation of rotavirus particles in 1969 and its evidence as an aetiology of severe dehydrating diarrhoea in infants and young children worldwide, the quest to find not only an acceptable and reliable but cost-effective vaccine has continued until now. Four live-attenuated oral rotavirus vaccines (LAORoVs) (Rotarix^®, RotaTeq^®, Rotavac^®, and RotaSIIL^®) have been developed and licensed to be used against all forms of rotavirus-associated infection. The efficacy of these vaccines is more obvious in the high-income countries (HIC) compared with the low- to middle-income countries (LMICs); however, the impact is far exceeding in the low-income countries (LICs). Despite the rotavirus vaccine efficacy and effectiveness, more than 90 countries (mostly Asia, America, and Europe) are yet to implement any of these vaccines. Implementation of these vaccines has continued to suffer a setback in these countries due to the vaccine cost, policy, discharging of strategic preventive measures, and infrastructures. This review reappraises the impacts and effectiveness of the current live-attenuated oral rotavirus vaccines from many representative countries of the globe. It examines the problems associated with the low efficacy of these vaccines and the way forward. Lastly, forefront efforts put forward to develop initial procedures for oral rotavirus vaccines were examined and re-connected to today vaccines.

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.

Rotavirus vaccination and intussusception - Science, surveillance, and safety: A review of evidence and recommendations for future research priorities in low and middle income countries

As of January 2016, 80 countries have introduced rotavirus vaccines into their national immunization programs. Many have documented significant declines in rotavirus-specific and all-cause diarrheal illnesses following vaccine introduction. Two globally licensed rotavirus vaccines have been associated with a low risk of intussusception in several studies. In July 2014, the Rotavirus Organization of Technical Allies Council convened a meeting of research and advocacy organizations, public health experts, funders, and vaccine manufacturers to discuss post-marketing intussusception surveillance and rotavirus vaccine impact data. Meeting objectives were to evaluate updated data, identify and prioritize research gaps, discuss best practices for intussusception monitoring in lower-income settings and risk communication, and provide insight to country-level stakeholders on best practices for intussusception monitoring and communication. Meeting participants agreed with statements from expert bodies that the benefits of vaccination with currently available rotavirus vaccines outweigh the low risk of vaccination-associated intussusception. However, further research is needed to better understand the relationship of intussusception to wild-type rotavirus and rotavirus vaccines and delineate potential etiologies and mechanisms of intussusception. Additionally, evidence from research and post-licensure evaluations should be presented with evidence of the benefits of vaccination to best inform policymakers deciding on vaccine introduction or vaccination program sustainability.

Intussusception Rates Before and After the Introduction of Rotavirus Vaccine

BACKGROUND

Recent US studies have identified a small increased risk of intussusception after rotavirus vaccination, mainly after the first dose. We examined trends in intussusception hospitalizations before (2000-2005) and after (2007-2013) rotavirus vaccine introduction to assess whether this observed temporal risk translates into more hospitalized cases at the population level.

METHODS

Intussusception hospitalizations in children <12 months of age were abstracted from the State Inpatient Database maintained by the Healthcare Cost and Utilization Project for 26 states that provided data from 2000 to 2013. Rates were calculated using bridged-race postcensal population estimates. Trends were analyzed by age groups (6-14 weeks, 15-24 weeks, and 25-34 weeks) based on the recommended ages for vaccine administration as well as 8-11 weeks when the majority of first doses are given. Rate ratios were calculated by using Poisson regression.

RESULTS

No consistent change in intussusception hospitalization rates was observed among all children <12 months of age and among children 15 to 24 weeks and 25 to 34 weeks of age. The intussusception hospitalization rate for children aged 8 to 11 weeks was significantly elevated by 46% to 101% (range: 16.7-22.9 per 100 000) in all postvaccine years except 2011 and 2013 compared with the prevaccine baseline (11.7 per 100 000).

CONCLUSIONS

The increase in the intussusception hospitalization rate in children 8 to 11 weeks when the majority of first doses of vaccine are given is consistent with recent US postlicensure studies. Given the magnitude of declines in rotavirus disease compared with this small increase in intussusception, the benefits of rotavirus vaccination outweigh the increase risk of intussusception.

Value of Post-Licensure Data on Benefits and Risks of Vaccination to Inform Vaccine Policy: The Example of Rotavirus Vaccines

In 1999, the first rhesus-human reassortant rotavirus vaccine licensed in the U.S. was withdrawn within a year of its introduction after it was linked with intussusception at a rate of ~1 excess case per 10,000 vaccinated infants. While clinical trials of 60,000-70,000 infants of each of the two current live oral rotavirus vaccines, RotaTeq (RV5) and Rotarix (RV1), did not find an association with intussusception, post-licensure studies have documented a risk in several high and middle income countries, at a rate of ~1-6 excess cases per 100,000 vaccinated infants. However, considering this low risk against the large health benefits of vaccination that have been observed in many countries, including in countries with a documented vaccine-associated intussusception risk, policy makers and health organizations around the world continue to support the routine use of RV1 and RV5 in national infant immunization programs. Because the risk and benefit data from affluent settings may not be directly applicable to developing countries, further characterization of any associated intussusception risk following rotavirus vaccination as well as the health benefits of vaccination is desirable for low income settings.

Retrospective surveillance for intussusception in children aged less than five years at two tertiary care centers in India

BACKGROUND

A rotavirus vaccine could soon become part of India's national immunization program. However the occurrence of intussusception due to rotavirus vaccine is a potential safety concern. This surveillance aimed at the collection of baseline data on childhood intussusception which would facilitate the monitoring of intussusception cases after the introduction of rotavirus vaccines.

METHODS

We retrospectively reviewed medical records of confirmed intussusception cases in children under the age of five, treated during 2007-2012 at two tertiary care hospitals attached to medical schools in India. Demographic, clinical, diagnostic and treatment practices data were obtained from hospital records.

RESULTS

Over a five to six year observation period, we identified 187 confirmed cases of intussusception, of which 75% were males. The median age of intussusception was 8 months, and we observed a possible trend in the distribution of cases with the highest number of cases being reported in the month of April and lowest in the month of October. The most common diagnostic methods used were ultrasonography and abdominal radiography with most cases being treated surgically (71%). The median length of hospital stay was 8 days (range 1-40) and mean was 10.2 days. Records of any fatality due to intussusception were not found during the review of the records.

CONCLUSIONS

This analysis provides an estimate of the baseline data of childhood intussusception prior to the introduction of the rotavirus vaccination as a part of routine immunization in India. A prospective surveillance system using a standardized case definition is needed in order to better examine the incidence of intussusception in developing countries.

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.

Intussusception incidence among infants in the UK and Republic of Ireland: a pre-rotavirus vaccine prospective surveillance study

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The pre-rotavirus vaccine incidence of intussusception among UK and Irish infants was 24.8 and 24.2/100,000 live births.

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The highest incidence (50.3/100,000 live births) occurred in the fifth month of life (for England).

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A seasonal trend in intussusception was observed with the incidence significantly increased during winter and spring.

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Baseline rates will inform rotavirus vaccine-safety policy by enabling comparison with post-introduction incidence.

Introduction

Intussusception, an abdominal emergency in young children, has been linked to a previous vaccine used to prevent rotavirus gastroenteritis. Although this vaccine was withdrawn, recent studies have suggested a potential, very small increased risk of intussusception following the administration of newly developed rotavirus vaccines. We aimed to determine the baseline incidence of intussusception among infants in the UK and Republic of Ireland – prior to the imminent introduction of the rotavirus vaccine into the UK schedule this year.

Methods

Prospective, active surveillance via the established British Paediatric Surveillance Unit (BPSU) was carried out from March 2008 to March 2009. Clinicians across 101 National Health Service (and equivalent) hospitals, including 27 paediatric surgical centres, reported cases admitted for intussusception in the UK and Republic of Ireland. The standard Brighton Collaboration case definition was used with only definite cases included for incidence estimation.

Results

The study response rate was 94.5% (379 questionnaires received out of 401 case notifications). A total of 250 definite cases of intussusception were identified. The annual incidence among infants in the UK and Republic of Ireland was 24.8 (95% CI: 21.7–28.2) and 24.2 (95% CI: 15.0–37.0) per 100,000 live births. In the UK, the highest incidence occurred in Northern Ireland (40.6, 95% CI: 21.0–70.8), followed by Scotland (28.7, 95% CI: 17.5–44.3), England (24.2, 95% CI: 20.9–27.9), then Wales (16.9, 95% CI: 6.8–34.8). In England, regional incidence was highest in London and lowest in the West Midlands. By age, the highest incidence (50.3/100,000 live births, 95% CI: 33.4–72.7) occurred in the fifth month of life (for England). A seasonal trend in the presentation of intussusception was observed with the incidence significantly (p = 0.001) increased during winter and spring.

Conclusion

The baseline rates obtained in this study will inform rotavirus vaccine-safety policy by enabling comparison with post-introduction incidence.

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).

The first rotavirus vaccine and the politics of acceptable risk

Context

Vaccination in the United States is a frequent source of controversy, with critics alleging failures by public health officials to adequately identify, monitor, and respond to risks associated with vaccines. In response to these charges, the case of RotaShield, a vaccine withdrawn in 1999 following confirmation of a serious adverse event associated with its use, is regularly invoked as evidence of the effectiveness of current vaccine safety activities.

Methods

This article examines the history of RotaShield, with particular attention paid to decision making regarding its use in the United States and internationally. I reviewed and analyzed federal advisory committee meeting transcripts, international conference reports, government and scientific publications, media coverage, and other primary and secondary source materials. I also conducted six semistructured interviews with former senior officials and advisory committee members at the U.S. Centers for Disease Control and Prevention who participated in decisions regarding the vaccine.

Findings

Decision making regarding RotaShield, including the ultimate withdrawal of its recommendation for use, was shaped significantly by government health officials’ concern for preserving public confidence in overall U.S. vaccination efforts amid several unrelated vaccine risk controversies ongoing at that time. This attention to public perception and external pressures occurred in tandem with the evaluation of the quantitative evidence regarding the magnitude and severity of the risk associated with the vaccine. The decisions made in the United States resulted in foreseen but unintended consequences for international use of the vaccine, including in nations where the profile of risks and potential benefits was dramatically different.

Conclusions

As enthusiasm for evidence-based decision making grows throughout medicine and public health, greater explicit attention should be directed to the processes by which decision makers and their expert advisers evaluate such evidence and translate it into regulation and policy by means of qualitative judgments.

Trends in intussusception hospitalizations among US infants before and after implementation of the rotavirus vaccination program, 2000-2009

BACKGROUND

Although US data have not documented an intussusception risk with current rotavirus vaccines, international data indicate a possible low risk, primarily after the first dose.

METHODS

Among infants in 26 US states comprising 75% of the birth cohort, we examined age-specific trends in population-level intussusception hospitalization rates before (2000-2005) and after (2007-2009) rotavirus vaccine introduction.

RESULTS

Compared with 2000-2005 (35.3 per 100,000), the rate was greater in 2007 (39.0 per 100,000; rate ratio [RR], 1.10; 95% confidence interval [CI], 1.04-1.18), similar in 2008 (33.4 per 100,000; RR, 0.95; 95% CI, .89-1.01), and lower in 2009 (32.9 per 100,000; RR, 0.93; 95% CI, .87-.99). Among infants aged 8-11 weeks, compared with 2000-2005 (6.9 per 100,000), a small, significant increase was observed in each of 2007 (11.4 per 100,000; RR, 1.64; 95% CI, 1.08-2.50), 2008 (12.2 per 100,000; RR, 1.76; 95% CI, 1.17-2.65), and 2009 (11.0 per 100,000; RR, 1.59; 95% CI, 1.04-2.44).

CONCLUSIONS

Following rotavirus vaccine introduction, a small increase in intussusception rates was seen among US infants aged 8-11 weeks, to whom most first doses of vaccine are given; no sustained population-level change in overall rates was observed.

Childhood intussusception in Uzbekistan: analysis of retrospective surveillance data

BACKGROUND

Estimates of baseline incidence of childhood intussusception could help safety monitoring after the introduction of rotavirus vaccines. We studied the incidence of intussusception in Uzbekistan, a GAVI-fund eligible state in Central Asia.

METHODS

We retrospectively reviewed intussusception cases in children <2 years of age treated during 2004-2008 at 15 hospitals in the Bukhara region of Uzbekistan. Demographic and clinical data as well as information on diagnostic and treatment practices were obtained from hospital records. We categorized cases using the Brighton collaboration clinical case definition and calculated the national incidence rate.

RESULTS

Over a 5-year study period, 67 confirmed cases were identified, of which 67% were boys. The median age was 12 months, and no seasonal trend in the distribution of cases was observed. The diagnostic methods used included abdominal radiography (87%) and ultrasonography (57%). Intussusception reduction by air enema was successful in 33 (49%) patients and 34 (50%) cases underwent surgery. A total of 4 deaths occurred, including 3 deaths in infants aged 0-6 months. The median length of hospital stay was 7.3 (range 0-37) days. The incidence of intussusception is estimated at 23 (95% CI 13.6-32.4) cases per 100,000 child-years, corresponding to approximately 237 cases annually.

CONCLUSIONS

This is the first study to estimate the incidence of childhood intussusception prior to the introduction of the rotavirus vaccination in Uzbekistan. A prospective surveillance system using a standardized case definition is needed in order to better examine the occurrence of intussusception in developing countries.

Radiology residents' experience with intussusception reduction

BACKGROUND

Residents should be exposed to adequate procedural volume to act independently upon completion of training. Informal inquiry led us to question whether residents encounter enough intussusception reductions to become comfortable with the procedure.

OBJECTIVE

We sought to determine radiology residents' exposure to intussusception reductions, and whether their experiences vary by region or institution.

MATERIALS AND METHODS

U.S. radiology residency program directors were asked to encourage their residents to complete a 12-question online survey describing characteristics of their pediatric radiology department, experiences with intussusception reduction, and confidence in their own ability to perform the procedure.

RESULTS

Six hundred sixty-four residents responded during the study period. Of those, 308 (46.4%) had not experienced an intussusception reduction, and 228 (34%) had experienced only one or two. Twenty-two percent of fourth-year residents had never experienced an intussusception reduction, and 21% had experienced only one. Among second- through fourth-year residents, only 99 (18.3%) felt confident that they could competently reduce an intussusception (P < 0.0001), and 336 (62.2%) thought they would benefit from a computer-assisted training model simulating intussusception reduction (P < 0.0001).

CONCLUSION

Radiology residents have limited opportunity to learn intussusception reduction and therefore lack confidence. Most think they would benefit from additional training with a computer-simulation model.

An interactive teaching device simulating intussusception reduction

Intussusception is relatively uncommon, occurring in 0.5 to 2.3 cases per 1,000 live births in the USA. Radiology residents, therefore, have few opportunities to participate in intussusception reduction during training, and practicing radiologists encounter it infrequently. Training is essential, as successful reduction avoids surgery. The judgment involved in reducing an intussusception is best gained with experience. We developed a training device that simulates fluoroscopic intussusception reduction with air. The device consists of a doll that contains a cylinder with similar stress and strain characteristics to the human colon. The trainee pumps air into the cylinder through a rectal tube using a standard hand-held air reduction pump. A sensor measures the pressure within the chamber and transmits readings to a computer, which displays images from actual intussusception reductions based on the pressure maintained within the device. A random component in the software gives the user a new experience each time and models uncertainties in the actual reduction process, including perforation. This intussusception reduction simulator can enhance resident education, giving residents the opportunity to practice this technique before employing it on a real patient. The simulator can also help practicing radiologists become more comfortable with intussusception air reduction.

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.

An Update of Paediatric Intussusception Incidence in Singapore: 1997-2007, 11 Years of Intussusception Surveillance

Introduction: Understanding baseline epidemiology of intussusception (IS) in different geographical settings is important for the safety assessment of rotavirus vaccines. This paper presents IS surveillance data from Singapore between 1997 and 2007, including the period between November 2005 and December 2007 when rotavirus vaccines (primarily Rotarix™) were available to newborns in Singapore. Materials and Methods: Case ascertainment, collection, analyses and presentation of IS data was done as per recommendations of the Brighton Collaboration Working Group. For estimating the IS incidence rate in infants, live births for the years of the study were used as denominators, while for incidence in children age <2 years, the expected numbers of infant deaths occurring between 1 and 2 years of age was deducted from the combined live births for the 2 years, to obtain the denominator. Results: The incidence of IS among children aged <1 year throughout this 10-year period was higher than the incidence of IS in children between 1 and 2 years of age. In 2005, 2006 and 2007, the incidence of IS per 100,000 was 39.9, 26.4 and 35.6 in children aged <1 year and 26.2, 23.8 and 28.7 in children <2 years. Conclusion: This IS surveillance study provides reassuring preliminary evidence that there is no increase in the incidence of IS in Singapore after the introduction of rotavirus vaccines (including Rotarix™) in Singapore. Key words: Epidemiology, Incidence, Rotarix, Rotavirus

The human rotavirus vaccine RIX4414 in infants: a review of safety and tolerability

BACKGROUND

An oral, live attenuated human rotavirus vaccine, RIX4414 has been developed to prevent rotavirus gastroenteritis. An integrated safety summary of 8 randomized, placebo-controlled, double-blind phase II and III trials of vaccine at potency licensed for use worldwide was performed.

METHODS

Healthy 1- to 18-week-old infants (N = 71209) were enrolled to receive 2 doses of RIX4414/placebo according to 0, 1 or 0, 2 month schedules. Solicited (fever, fussiness/irritability, loss of appetite, vomiting, diarrhea, cough/rhinorrhea) and unsolicited adverse events (AEs) were recorded for 8 days and 31 days, respectively, after each dose. Serious adverse events (SAEs) including intussusception and death were collected throughout the entire study periods. Potential imbalances were defined as the 95% confidence interval (CI) for the relative risk (RR) stratified by trials excluding "1."

RESULTS

Solicited AEs were evaluated in 3286 RIX4414 vaccinees and 2015 placebo recipients. Among solicited AEs, no imbalance was noted between groups. SAEs, including death and intussusception, were evaluated in 36755 RIX4414 and 34454 placebo recipients. Within 31 days after each dose, no imbalances were noted between the groups for all SAEs (RR = 0.9; 95% CI: 0.81, 1.01), deaths (RR = 1.64; 95% CI: 0.92, 3.02), and intussusception (RR 1.23; 95% CI: 0.41, 3.90). SAEs because of gastrointestinal diseases including diarrhea, gastroenteritis (all cause and due to rotavirus), dehydration, and intestinal ileus occurred significantly less often in RIX4414 than placebo recipients.

CONCLUSIONS

Across the phase II and III clinical trials, the reactogenicity and safety profile between RIX4414 and placebo was similar, in particular with no increased risk of intussusception.

Evaluating the safety of a rotavirus vaccine: the REST of the story

The Rotavirus Efficacy and Safety Trial (REST) was a blinded, placebo-controlled study of the live pentavalent human-bovine vaccine, RotaTeq® (Merck & Co. Inc., West Point, PA). REST was noteworthy because its primary objective was to evaluate the safety of RotaTeq® with regard to intussusception, a rare intestinal illness that occurs with a background incidence of approximately 50 cases per 100 000 infant years. The study involved approximately 70 000 infants at over 500 study sites in 11 countries. The study demonstrated that the risk of intussusception was similar in vaccine and placebo recipients and that the vaccine prevented rotavirus gastroenteritis, ameliorated the severity of disease in those who had any disease, and substantially reduced rotavirus-associated hospitalizations and other health care contacts. This report provides an in-depth review of the background, statistical and regulatory considerations, and execution of REST. We describe the rationale and methods used for sample size, continuous safety monitoring, group sequential design, and detailed study execution. The results of the study have been reported elsewhere. The design and conduct of this study may serve as a useful model for planning other future large-scale clinical trials, especially those evaluating uncommon adverse events.

The Epidemiology of Paediatric Intussusception in Singapore: 1997 to 2004

Introduction: The world’s first rotavirus vaccine, Rotashield® or RRV-TV, was registered in the US in 1998, but withdrawn within a year because of an observed association with intussusception (IS). Surveillance for IS has consequently become important in safety monitoring of new-generation rotavirus vaccines during development. Post-marketing surveillance is also important, and requires the availability of local baseline epidemiology data on IS. Materials and Methods: An eight-year study of IS in children under 2 years of age in Singapore was performed by retrospective review of admissions to KK Women’s and Children’s Hospital, the main paediatric hospital, from 1997 to 2001, followed by prospective surveillance of all hospitals from 2001 to 2004, using the case definition of the Brighton Collaboration Intussusception Working Group. Results: The average IS incidence was 60 per 100,000 in under-ones, and 32 per 100,000 in under-twos, with a downward trend between 1999 and 2004. Ninety-two per cent of subjects were aged below one year, with 51% aged 6 months to 11 months. The mean age at which IS occurred increased from 6.4 months to 12.5 months over the study period. The male-to-female ratio was 1.3:1. No trend in IS numbers was observed over different months of the year. Conclusion: IS in Singapore shows no seasonality, but has demonstrated a trend of decreasing incidence in recent years. While highest in the first year of life, the risk of IS is increasing in the second year of life. Males have a slightly higher risk. Key words: Adverse effects, Rotavirus vaccines

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.

Rotavirus vaccine: early introduction in Latin America-risks and benefits

Rotavirus infection is the cause of severe gastroenteritis of young children worldwide, leading to an estimate of 600,000 deaths a year. Efforts to develop an effective and safe vaccine resulted in licensing in 1998 of a live oral vaccine (RotaShield) that was withdrawn less than 1 year later when reports of cases of intussusception were linked to its application. This led to development of new rotavirus vaccine candidates that are currently in late phase III clinical trials. One of these vaccines, GlaxoSmithKline's Rotarix, was licensed in July 2004 to be used in Mexico. This review describes the general background for rotavirus vaccine development, the different vaccine candidates that have been tested or are currently being evaluated, the association of rotavirus vaccination with the bowel blockage known as intussuception, and discusses the benefits and risks of the fast-track introduction of Rotarix in Latin America, and particularly in Mexico.

The Rotavirus Vaccine Saga

Rotavirus is the single most common cause of acute, dehydrating gastroenteritis worldwide. This is a highly contagious and highly democratic disease. The attack rate in infants and young children is similar regardless of sanitation, socioeconomics or geography. Rotavirus vaccine development began in the early 1980s using a "Jennerian" approach based on rotaviruses that normally infect animals. Although these vaccines were found to be generally safe, protection from disease was inconsistent. The second generation of vaccines was based on the same animal viruses configured to carry the relevant coat proteins of human rotaviruses. An attenuated human rotavirus vaccine has also been developed. After close to 20 years of laboratory and clinical studies, safe and effective rotavirus vaccines are approaching regulatory approval.

Neonatal administration of rhesus rotavirus tetravalent vaccine

BACKGROUND AND AIMS

Administration of the first dose of rhesus rotavirus-based tetravalent (RRV-TV) vaccine is followed by a transient febrile reaction at 3-4 days postvaccination in about one-third of vaccinees. We hypothesized that giving the first dose of RRV-TV vaccine during the neonatal period might reduce the reactogenicity of RRV-TV vaccine without compromising the utilization of the vaccine.

METHODS

A double blind placebo-controlled safety and immunogenicity trial of 90 infants who received RRV-TV vaccine at 0-4-6, 0-2-4 or 2-4-6 months of age was conducted. Reactions were evaluated for 1 week after each vaccination and, in addition, serum specimens were collected before vaccination and at 5 and 7 months of age.

RESULTS

Febrile reactions were not observed in 62 infants receiving the first dose of RRV-TV vaccine during the neonatal period. Five of the 28 (18%) infants receiving the first dose at 2 months were febrile on 1 or more days, whereas none of the 30 infants who had received a neonatal dose developed a fever when vaccinated again at 2 months of age. An enzyme-linked immunosorbent assay IgA antibody response after 3 doses was observed significantly less frequently (77%) in infants who had received a neonatal dose, a second dose at 2 months of age, and a third dose at 4 months of age compared with those who received their first dose at 2 months and a second dose at 4 months (100%, P < 0.02). Also, the frequency of a neutralizing antibody response to RRV and human rotavirus serotypes G1-4 tended to be lower in the group that had received the vaccine at 0-2-4 months compared with those who received it at 2-4-6 months. When the 2 tests were combined, the frequency of a seroresponse following the 0-2-4 month schedule (94%) was comparable with that following the 2-4-6 month schedule (100%).

CONCLUSION

Infants who received the first dose of RRV-TV vaccine during the neonatal period did not develop a febrile reaction. The immune response in a 3-dose schedule initiated in the neonatal period is somewhat dampened but still acceptable. Neonatal immunization might also reduce the very small risk of intussusception, which has been associated with administration of RRV-TV vaccine to older infants.

A Rotavirus Vaccine for Infants: The Asian Experience

Introduction: Severe rotavirus gastroenteritis in children causes significant morbidity world- wide and substantial deaths in developing countries. Hence, a live attenuated vaccine Rotarix™ was developed with human strain RIX4414 of G1P1A P[8] specificity. RIX4414 trials in infants have begun in developed and developing countries worldwide. An overview of RIX4414 in developed and developing countries and prospects with this vaccine in Asia are presented. Methods: Completed RIX4414 trials have been reviewed. Results: Two oral doses of RIX4414 were well tolerated with a reactogenicity profile similar to placebo. RIX4414 was also highly immunogenic, e.g., in a dose-ranging study conducted in Singapore, 98.8% to100% of infants had a vaccine take after 2 doses. RIX4414 did not affect the immune response of simultaneously administered routine infant vaccines. RIX4414 significantly reduced severe rotavirus gastroen- teritis in settings where multiple serotypes including the emerging G9 type co-circulated. Conclusion: These encouraging results warrant further evaluation of the vaccine worldwide and especially in developing countries with the highest need. Therefore, evaluation of the Rotarix™ vaccine is continuing in large phase III trials in Asia and worldwide. Key words: Asia, Attenuated, Developing countries, Gastroenteritis, RIX4414

Safety and efficacy of a pentavalent human-bovine (WC3) reassortant rotavirus vaccine

BACKGROUND

Rotavirus is a leading cause of childhood gastroenteritis and death worldwide.

METHODS

We studied healthy infants approximately 6 to 12 weeks old who were randomly assigned to receive three oral doses of live pentavalent human-bovine (WC3 strain) reassortant rotavirus vaccine containing human serotypes G1, G2, G3, G4, and P[8] or placebo at 4-to-10-week intervals in a blinded fashion. Active surveillance was used to identify subjects with serious adverse and other events.

RESULTS

The 34,035 infants in the vaccine group and 34,003 in the placebo group were monitored for serious adverse events. Intussusception occurred in 12 vaccine recipients and 15 placebo recipients within one year after the first dose including six vaccine recipients and five placebo recipients within 42 days after any dose (relative risk, 1.6; 95 percent confidence interval, 0.4 to 6.4). The vaccine reduced hospitalizations and emergency department visits related to G1-G4 rotavirus gastroenteritis occurring 14 or more days after the third dose by 94.5 percent (95 percent confidence interval, 91.2 to 96.6 percent). In a nested substudy, efficacy against any G1-G4 rotavirus gastroenteritis through the first full rotavirus season after vaccination was 74.0 percent (95 percent confidence interval, 66.8 to 79.9 percent); efficacy against severe gastroenteritis was 98.0 percent (95 percent confidence interval, 88.3 to 100 percent). The vaccine reduced clinic visits for G1-G4 rotavirus gastroenteritis by 86.0 percent (95 percent confidence interval, 73.9 to 92.5 percent).

CONCLUSIONS

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.)

Intussusception among young children in Europe

Intussusception, a potentially lethal condition with poorly understood etiology, is the most common cause of acute intestinal obstruction in children younger than 5 years old. In some cases, the condition has been associated with administration of the first licensed rotavirus vaccine, the reassortant rhesus-human tetravalent rotavirus vaccine (RRV-TV; RotaShield). No such association has to date been reported from large phase III safety trials with new rotavirus vaccines. As 2 new, live-attenuated oral rotavirus vaccines are currently under review for approval by the European Union regulatory authorities, a review of the clinical, etiologic and epidemiologic aspects of intussusception in Europe is urgently needed. We conducted a review of Medline literature, published from 1995 onwards on intussusception in the World Health Organization's European Region. The results are compared with data from previous reviews and other regions. The classic triad of intussusception symptoms (abdominal pain, abdominal mass, bloody stools) was present in 29-33% of patients according to the medical literature reviewed. Conservative treatment (barium, air or saline enema) was the rule (81% of cases), and few complications were observed during treatment. Treatment outcome was generally favorable, with recurrence occurring in approximately 1 in 10 patients, and only 1 death reported. Structural lead points were seen in 3% of patients; no other reliable data on the etiology of intussusception were found. The incidence of acute intussusception in young children in Europe, according to 6 heterogeneous hospital-based studies, ranged from 0.66 to 2.24 per 1000 children in inpatient departments and from 0.75 to 1.00 per 1000 children in emergency departments. Peak incidences were found in children 3-9 months of age. There are still gaps in our knowledge of intussusception with respect to its etiology and especially by which mechanisms RRV-TV might have caused it to occur. Data from regions outside Europe showed that rotavirus infection and disease are not associated with intussusception. As new rotavirus vaccines become available for use in Europe, postlicensure surveillance for intussusception is indicated and may be instrumental in further understanding the epidemiology of this condition and in further assessing the safety of future vaccines.

More on RotaShield and intussusception: the role of age at the time of vaccination

BACKGROUND

RotaShield, a vaccine intended to prevent severe rotavirus diarrhea, was withdrawn in July 1999, 9 months after it became available in the United States, because of a temporal association with intussusception events that occurred in vaccinated infants. We explore here the effect of age on the risk of intussusception.

METHODS

We reanalyzed a case-control database of the Centers for Disease Control and Prevention by use of a 21-day window, to define vaccine-associated events. We obtained data on vaccine use from the National Immunization Survey and estimated the age-stratified background incidence of intussusception by use of Healthcare Cost and Utilization Project data. We combined these data to estimate how absolute risk varies with age and to model the projected population-attributable risk associated with 3 different vaccination schedules.

RESULTS

We found that the incidence of intussusception associated with the first dose of vaccine increased with age. Infants > or = 90 days old accounted for 80% of cases of intussusception associated with a first dose but had received only 38% of first doses. Modeling of the recommended schedule of vaccination at ages 2, 4, and 6 months projected 1 intussusception event/11,000-16,000 vaccine recipients; modeling of a 2-dose schedule beginning in the neonatal period projected 1 intussusception event/38,000-59,000 vaccine recipients.

CONCLUSIONS

The practice of initiating immunization after age 90 days, which we call "catch-up" vaccination, contributed disproportionately to the occurrence of intussusception associated with the use of RotaShield. A fully implemented 2-dose vaccination schedule begun during the neonatal period would lead to, at most, a 7% increase in the incidence of intussusception above the annual background incidence.

Intussusception and rotavirus associated hospitalisation in New Zealand

AIMS

To describe the epidemiology of intussusception and its relation to rotavirus associated hospitalisation in New Zealand.

METHODS

National hospital discharge data between January 1998 and June 2003 for all children younger than 3 years of age with intussusception were reviewed. Independently, children from the same age group, admitted to eight paediatric units with rotavirus gastroenteritis between May 1998 and May 2000, were identified prospectively. Epidemiological characteristics of cases with intussusception were compared with those of hospitalised rotavirus disease.

RESULTS

During the 5.5 year study period, there were 277 cases of intussusception and no deaths. Most (72%) occurred in the first year of life (age adjusted incident rate 65 per 100,000 child-years, 95% CI 56 to 74). Risk of intussusception was less in females (risk ratio 0.58; 95% CI 0.43 to 0.78) and for Maori (risk ratio 0.52; 95% CI 0.35 to 0.77) when compared with European infants. In contrast to hospitalised rotavirus cases, intussusception peaked at a younger age and lacked seasonality.

CONCLUSIONS

This study provides national baseline data on intussusception for future rotavirus vaccine programmes in New Zealand. Wild-type rotaviruses do not appear to have a major role in triggering intussusception. Prospective surveillance systems, using standardised case definitions and nested case-control methodology, are needed to further our understanding of the aetiology and epidemiology of intussusception.

Development of a Pentavalent Rotavirus Vaccine against Prevalent Serotypes of Rotavirus Gastroenteritis

The strategy of decreasing the morbidity and mortality associated with rotavirus gastroenteritis through vaccination is supported by studies demonstrating that wild-type rotavirus infection protects against subsequent rotavirus disease. Primary infection with wild-type rotavirus typically induces homotypic immunity. Vaccination of infants with a multivalent vaccine directed against prevalent rotavirus serotypes is the strategy most likely to provide the broadest degree of protection against rotavirus gastroenteritis. The pentavalent human-bovine reassortant rotavirus vaccine (HBRV) is directed against each of the most prevalent rotavirus serotypes, including G1, G2, G3, G4, and P1. The safety, immunogenicity, and efficacy of different reassortant compositions and formulations of the HBRV have been evaluated in clinical trials. An HBRV dose of > or =8 x 10(6) plaque-forming units has demonstrated 68.8%-76.6% efficacy against any rotavirus gastroenteritis, regardless of severity, and approximatel 100% efficacy against severe rotavirus gastroenteritis for the first rotavirus infection season after vaccination. The HBRV has been generally well tolerated, with no increase in the incidence of fever, vomiting, diarrhea, or behavioral changes among vaccine recipients, compared with placebo recipients, during the 14- and 42-day periods after administration of any dose. Shedding of vaccine strains in feces is uncommon. A large-scale trial is under way to evaluate the efficacy and safety of the manufacturing-scale formulation of pentavalent HBRV.

Evaluation of RIX4414, A Live, Attenuated Rotavirus Vaccine, in a Randomized, Double‐Blind, Placebo‐Controlled Phase 2 Trial Involving 2464 Singaporean Infants

BACKGROUND

At present, no rotavirus vaccine is commercially available for use worldwide. Hence, a live, attenuated monovalent vaccine was developed with human strain RIX4414 (G1P1A P[8] specificity). Vaccination trials involving infants are ongoing in developed and developing countries.

METHODS

This study was a randomized, double-blind, placebo-controlled trial conducted at pediatric hospitals and polyclinics in Singapore for the evaluation of the immunogenicity, reactogenicity, and efficacy of 2 oral doses of RIX4414. In total, 2464 healthy infants (who were 11-17 weeks old when the first dose was administered, which is in accordance with the local immunization schedule) were enrolled to receive RIX4414 at 3 concentrations of virus (10(4.7), 10(5.2), or 10(6.1) focus-forming units) or placebo at 1-month intervals, concomitantly with routinely administered infant vaccines.

RESULTS

The RIX4414 vaccine was highly immunogenic, and virtually all vaccine recipients (98%-100%) experienced "vaccine take" (i.e., a combined immunogenicity end point based on seroconversion and/or shedding of RIX4414 in postvaccination stool samples) after receipt of 2 doses at all 3 dosage levels. Depending on the virus concentration, the anti-rotavirus IgA seroconversion rate varied from 76% (95% confidence interval [CI], 68%-83%) to 91% (95% CI, 85%-95%). Two doses of RIX4414 were well tolerated, with no increase in high fever, severe diarrhea, or vomiting after either dose or with increased viral concentration, compared with placebo. There was no observed interference with routine vaccinations of infants when RIX4414 was coadministered. The calculated efficacy of RIX4414 against rotavirus gastroenteritis was 82% (P = .046); however, this result was considered to be of limited conclusive value because of the low number of rotavirus gastroenteritis episodes identified during the follow-up period.

CONCLUSIONS

The live, attenuated rotavirus vaccine (RIX4414) was well tolerated and highly immunogenic in Singaporean infants. The immunogenicity of routinely administered infant vaccines was not impaired by concomitant administration of RIX4414 vaccine.