ESPID Reports and Reviews

Intussusception and Rotavirus Vaccines Consensus on Benefits Outweighing Recognized Risk Jim P. Buttery, MB BS, MD, MSc,*†‡ Jane Standish, MB BS, FRACP,*†‡§ and Julie E. Bines, MB BS, MD, FRACP‡§

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ince licensure in 2006, the rotavirus vaccines, RV5 (pentavalent bovine-human reassortant vaccine, Rotateq, Merck) and RV1 (attenuated monovalent human rotavirus vaccine, Rotarix, GSK Biologicals), have reduced morbidity and mortality from acute gastroenteritis in young children. Consensus on these vaccines having a small increased risk of intussusception after the first 1 or 2 doses has slowly emerged, with the risk benefit equation strongly favoring benefit in both developed and developing settings.

Idiopathic intussusception is an uncommon condition, with marked international and ethnic variation in rates, as well as changing incidence over time in many countries. Rates in the first year of life vary from 9 per 100,000 in Bangladesh, up to 328 per 100,000 in South Korea.1 Recent US incidence estimates appear stable around 35 per 100,000 since 2000, with rates before this period 25% higher.2 Intussusception presentations are relatively constant throughout the year, with minimal seasonality demonstrated.1

INTUSSUSCEPTION: ETIOLOGY AND EPIDEMIOLOGY

INTUSSUSCEPTION AND WILD TYPE ROTAVIRUS

Intussusception is an acute bowel obstruction because of the telescoping of 1 part of the bowel into an adjacent section, resulting in obstruction and reduced blood flow. Typically presenting in infants aged 4–9 months, intussusception can occur at any age. Most cases can be diagnosed by ultrasonography, contrast enemas and reduced using air enemas. Later presentations may require surgery for intussusception reduction or resection. Untreated, it can result in bowel necrosis, perforation and may be fatal. Outside the peak age, anatomic lead points such as polyps can be identified as the cause of intussusception. However, in infancy, idiopathic intussusception is most common. Multiple investigations have explored the etiology of idiopathic intussusception, with adenoviruses implicated in up to 40% of cases.1 From the *Department of Infectious Diseases, Monash Children’s Hospital, Monash Health; †Department of Paediatrics, Monash University; ‡Murdoch Childrens Research Institute; and §Department of Paediatrics, University of Melbourne, Royal Children’s Hospital, Victoria, Australia. J.P.B. and J.E.B. have acted as chief investigators for epidemiologic studies sponsored by vaccine manufacturers (CSL, Merck) or serologic testing provided (J.P.B.: Merck). They have served on data safety monitoring boards for CSL (J.P.B.) and Merck (J.E.B.). All payments are to administrative funds held by Murdoch Childrens Research Institute. The author have no other funding or conflicts of interest to disclose. Address for correspondence: Jim Buttery, MB BS, MD, MSc, Department of Infectious Diseases, Monash Children’s Hospital, 246 Clayton Rd, Clayton, Victoria, 3168 Australia. E-mail: [email protected]. Copyright © 2014 by Lippincott Williams & Wilkins ISSN: 0891-3668/14/3307-0772 DOI: 10.1097/INF.0000000000000359

The role of natural rotavirus infection in intussusception was first proposed in the 1978 by Japanese investigators using electron microscopic examination of feces. These findings were not able to be replicated across a variety of case-series and case-control studies as well as epidemiologic studies in temperate settings, where the marked seasonal rotavirus gastroenteritis peak was not accompanied by similar rises in intussusception cases.1

RRV-TV AND INTUSSUSCEPTION The first licensed rotavirus vaccine, rhesus rotavirus reassortant tetravalent vaccine (RRV-TV, Rotashield, Wyeth Vaccines) was introduced into the US infant immunization schedule in October 1998. Reassortant vaccines use the segmented rotavirus genome to incorporate human rotavirus genes coding for surface proteins into the genome of animal rotavirus strains, which are rarely pathogenic to humans, creating an animal-human reassortant strain. RRV-TV was a mix of four rhesus-human reassortant strains, expressing human rotavirus G1-4 surface proteins. Prelicensure trials identified more intussusception cases in the RRV-TV arm compared with placebo, which was not statistically significant. However, intussusception was included as a potential adverse event after immunization in the product information. By March 1999, the US Vaccine Adverse Event Reporting Scheme (VAERS) had received 15 reports of intussusception. After initial examination, the Centre for Disease Control recommended suspending further vaccinations in July 1999 pending further investigations, with the manufacturer

voluntarily ceasing distribution. After review of several investigations, the US Advisory Committee on Immunization Practices withdrew its recommendation that RRV-TV be administered at 2,4 and 6 months, because of a significantly raised association with intussusception, especially after the first dose. Casecontrol and case-series studies indicated the odds of intussusception cases having received a first dose of RRV-TV 3–7 days prior were as high as 37.2, with the risk period extending from 3 to 14 days postvaccination. (Table 1) This corresponded to an estimated excess of 1 additional case per 4670–9474 infants vaccinated, and risk appeared increased with administration of first dose after 3 months of age.3 However, ecologic studies suggested a much lower population attributable risk.

SECOND-GENERATION VACCINES: RV5 AND RV1 The RRV-TV experience informed the clinical development programs of RV5 and RV1. Both underwent massive phase III safety trials, with sample sizes to detect an association with intussusception similar to that observed with RRV-TV. Trials of over 60,000 infants each demonstrated no association with intussusception, with both vaccines licensed in 2006. Over the next 2 years, rotavirus vaccination was implemented in many countries including the United States, Mexico, Brazil, Australia and some European nations, with strict guidelines around age at dosing. However, given the limitation of these studies to detect an association at a lower level than RRV-TV, post-licensure studies were conducted in multiple settings to ensure early detection of any association, across nations with varying background rates of intussusception. These included enhanced passive surveillance to regulatory and clinical reporting systems, usage of large population administrative datasets and active case-finding programs in pediatric hospitals. The first suggestion of an association was reported in Australia, with both RV5 and RV1 showing an excess of observed intussusception cases after dose 1 compared with expected number of cases based on historical rates. The small numbers and potential bias in the study relating to use of historical rates necessitated further confirmation. Subsequently, case-control studies from Mexico

The ESPID Reports and Reviews of Pediatric Infectious Diseases series topics, authors and contents are chosen and approved independently by the Editorial Board of ESPID.

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The Pediatric Infectious Disease Journal  •  Volume 33, Number 7, July 2014

The Pediatric Infectious Disease Journal  •  Volume 33, Number 7, July 2014

ESPID Reports and Reviews

TABLE 1.  Post-licensure Analyses of Intussusception After Rotavirus Vaccination Setting United States

Mexico

Data Source

Study Design

Vaccine Dose

VAERS Mini-sentinel: administrative datasets

Case-control SCRI Cohort Cohort SCRI SCRI

RRV-TV RV5 RV5 RV1 RV5 RV1

VAERS Active surveillance

Brazil Active surveillance Australia Active surveillance Active surveillance/ administrative datasets

SCRI Observed versus expected SCRI

RV1 RV5 RV1 RV5 RV5 RV5 RV1 RV1 RV1

1 1 1 2 1 1 2 2 2 1 1 1 1 2 1 1 2

Risk period- Day post dose

Ratio

3–14 1–7 1–7 1–21 3–6 1–7 8–14 15–21 1–7 1–7 1–7 1–7 8–21 1–7 1–7 8–21 1–7

OR 37.2 RR 7.0 RR 2.9 RR 4.6 DRR 3.8 IR 5.3 IR 2.2 IR 2.2 IR 2.6 RR 5.3 RR 3.5 RR 9.9 6.3 2.8 6.8 3.5 2.8

95% Confidence Estimated excess IS Interval cases per 105* 12.6–110.1 1.7–29 1.4–6.0 1.5–15 1.9–7.4 3.0–9.3 1.1–4.2 1.2–4.0 1.3–5.2 1.1–15.4 0.7–10.1 3.7–26.4 2.8–14.4 1.2–6.8 2.4–19.0 1.3–8.9 1.1–7.3

10–20

0.79 1.9 1.8 7.0

Reference Murphy et al3 Yih et al10 Haber et al 4 Patel et al 11

Buttery et al12 Carlin et al5

4.3

OR, odds ratio; RR, risk ratio; DRR, daily reporting ratio; IR, incidence ratio. *Estimated excess per 100,000 children after full course of vaccination (3 doses of RV5 or 2 doses of RV1). Mexico and Brazil rates calculated using national birth statistics for 2011.11

and Brazil confirmed an association with RV1 dose 1 and dose 2. However, despite using multiple data sources and methodologies, an association in the United States with RV5 was not able to be confirmed until 2013, when VAERS reports were examined using the selfcontrolled risk interval (SCRI) methodology where the patient is used as their own control, comparing the risk of intussusception in the postvaccine period with other periods.4 SCRI and case-control methodologies from a larger dataset have since confirmed the original Australian findings (Table 1).5

BENEFIT VERSUS RISK Although the evidence for the risk of intussusception has evolved, the benefits of rotavirus immunization have been rapidly and consistently demonstrated in developed and developing settings. Despite reduced vaccine efficacy in developing setting trials, reductions in mortality in children

Intussusception and rotavirus vaccines: consensus on benefits outweighing recognized risk.

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