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

Human and bovine rotavirus strain antigens for evaluation of immunogenicity in a randomized, double-blind, placebo-controlled trial of a single dose live attenuated tetravalent, bovine-human-reassortant, oral rotavirus vaccine in Indian adults

A single dose of live attenuated tetravalent (G1-G4) bovine human reassortant rotavirus vaccine (BRV-TV) was administered to healthy Indian adult volunteers, who were assessed for safety and immunogenicity of the vaccine with 3:1 randomization to vaccine or placebo. All 20 adult male volunteers in the study had rotavirus specific serum IgA at baseline. There were no side effects or adverse events reported. Administration of BRV-TV was not associated with fever, diarrhea, or altered liver transaminases. Rotavirus IgA seroconversion post single dose administration was 27%. This study shows that BRV-TV is non-reactogenic, safe and immunogenic in adults. The IgA units estimated for the same sample using human G1P[8] rotavirus strain as the antigen were consistently higher than with the bovine G6P[5] WC3 strain and the human G2P[4] DS-1 strain antigen. The use of different human and bovine rotavirus strains as antigens in a quantitative rotavirus specific serum IgA assay resulted in different estimations of IgA antibody in the same sample.

A phase I clinical trial of a new 5-valent rotavirus vaccine

We conducted a phase I, double-blind, placebo-controlled trial to evaluate a new 5-valent oral rotavirus vaccine's safety and immunogenicity profiles. Subjects were randomly assigned to receive 3 orally administered doses of a live-attenuated human-bovine (UK) reassortant rotavirus vaccine, containing five viral antigens (G1, G2, G3, G4 and G9), or a placebo. The frequency and severity of adverse events were assessed. Immunogenicity was evaluated by the titers of anti-rotavirus IgA and the presence of neutralizing antibodies anti-rotavirus. No severe adverse events were observed. There was no difference in the frequency of mild adverse events between experimental and control groups. The proportion of seroconversion was consistently higher in the vaccine group, for all serotypes, after each one of the doses. The 5-valent vaccine has shown a good profile of safety and immunogenicity in this small sample of adult volunteers.

Resistance to rotavirus infection in adult volunteers challenged with a virulent G1P1A[8] virus correlated with serum immunoglobulin G antibodies to homotypic viral proteins 7 and 4

BACKGROUND

In a study performed in 1983, 18 adult volunteers received oral challenge with the virulent human rotavirus strain D (G1P1A[8],NSP4[B]). To identify correlates of resistance to rotavirus infection, we analyzed levels of serum immunoglobulin (Ig) A and IgG antibodies to various rotaviral antigens in 16 of the 18 volunteers.

METHODS

We used immunocytochemical assays that involved a total of 16 different recombinant baculoviruses, with each baculovirus expressing one of the following major serotype/genotype rotavirus proteins for the serologic assays: (1) viral protein (VP) 4 with P1A[8], P1B[4], P2A[6], P3[9], or P4[10] specificity; (2) VP7 with G1-G4 or G9 specificity; and (3) nonstructural viral protein (NSP) 4 with genotype A, B, C, or D specificity.

RESULTS

The prechallenge titers of IgG antibody to VP7 types G1, G3, G4, and G9; VP4 types P1A[8], P1B[4], P2A[6], and P4[10]; and NSP4 type [A] in the group of noninfected volunteers (n = 11) were significantly higher than those in the group of infected volunteers (n = 5; of these 5 volunteers, 4 were symptomatically infected). Moreover, logistic regression analysis showed that resistance to rotavirus infection most closely correlated with higher prechallenge titers of IgG antibody to homotypic VP7 (G1) and VP4 (P1A[8]).

CONCLUSIONS

These results suggest that protection against rotavirus infection and disease is primarily VP7/VP4 homotypic and, to a lesser degree, heterotypic.

Diversity of human rotaviruses detected in Sicily, Italy, over a 5-year period (2001-2005)

Rotavirus infection was detected in 39.9% of 1030 children hospitalized with gastroenteritis in Palermo, Italy, in the period 2001-2005. Rotavirus strains belonging to G1, G4 and G9 types were continually detected, with G1 being the most common type in 2001, 2002 and 2004. A G4 epidemic occurred in 2003, while G9 was predominant in 2005. G2 strains displayed a low prevalence, except in 2003. G3 rotaviruses accounted for 2.7-17% of the gastroenteritis episodes in 2002-2005. The P-type of a subset of 166 strains confirmed the circulation of the usual G/P combinations, but single G1P[6], G9P[9] and G6P[9] strains were also found.

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.

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.

Rotavirus Vaccines: Targeting the Developing World

For the past 2 decades, rotavirus infection, the most common cause of severe diarrhea in children, has been a priority target for vaccine development. This decision to develop rotavirus vaccines is predicated on the great burden associated with fatal rotavirus disease (i.e., 440,000 deaths/year), the firm scientific basis for developing live oral vaccines, the belief that increased investment in development at this time could speed the introduction of vaccines in developing countries, and the appreciation that implementation of a vaccine program should result in a measurable decrease in the number of hospitalizations and deaths associated with rotavirus disease within 2-3 years. RotaShield (Wyeth-Ayerst), the first rotavirus vaccine licensed in the United States, was withdrawn after 9 months because of a rare association of the vaccine with the development of intussusception. In the developing world, this vaccine could still have had a measurable effect, because the benefits of preventing deaths due to rotavirus disease would have been substantially greater than the rare risk of intussusception. Two live oral vaccines being prepared by GlaxoSmithKline and Merck have completed large-scale clinical trials. The GlaxoSmithKline vaccine has been licensed in Mexico and the Dominican Republic, and the Merck vaccine could be licensed in the United States within 1 year; several other candidate vaccines are in earlier stages of testing. However, many challenges remain before any of these vaccines can be incorporated into childhood immunization programs in the developing world. First, vaccine efficacy, which has already been demonstrated in children in industrialized and middle-income countries, needs to be proven in poor developing countries in Africa and Asia. The safety of vaccines with regard to the associated risk of intussusception must be demonstrated as well. Novel financing strategies will be needed to ensure that new vaccines are affordable and available in the developing world. Decision makers and parents in developing countries need to know about this disease that has little name recognition and is rarely diagnosed. Finally, for the global effort toward the prevention of rotavirus disease to be successful, special efforts will be required in India, China, and Indonesia, because one-third of all deaths due to rotavirus disease occur in these countries, and because these countries depend almost entirely on vaccines manufactured domestically.

Rotavirus vaccines: an update

PURPOSE OF REVIEW

Rotavirus infection is the most common cause of severe diarrhea disease in infants and young children worldwide and has a major global impact on childhood morbidity and mortality. Vaccination is the only control measure likely to have a significant impact on the incidence of severe dehydrating rotavirus disease.

RECENT FINDINGS

Rotavirus disease prevention efforts suffered a great setback in 1999 with the withdrawal of the RRV-TV vaccine less than a year after its introduction. Several new rotavirus vaccine candidates have now been developed and are undergoing clinical trials.

SUMMARY

New safe and effective rotavirus vaccines offer the best hope of reducing the toll of acute rotavirus gastroenteritis in both developed and developing countries.

Rotavirus vaccine for preventing diarrhoea

BACKGROUND

Rotaviruses cause viral gastroenteritis and result in more deaths from diarrhoea in children under 5 years of age than any other single agent, particularly in low- and middle-income countries.

OBJECTIVES

To assess rotavirus vaccines in relation to preventing rotavirus diarrhoea, death, and adverse events.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group's trial register (October 2003), the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2003), MEDLINE (1966 to October 2003), EMBASE (January 1980 to October 2003), LILACS (1982 to October 2003), Biological Abstracts (January 1982 to October 2003), reference lists of articles, and contacted researchers and rotavirus vaccine manufacturers.

SELECTION CRITERIA

Randomized controlled trials comparing rotavirus vaccines to placebo, no intervention, or other rotavirus vaccines in children and adults.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed trial methodological quality, and contacted trial authors for additional information.

MAIN RESULTS

Sixty-four trials provided information on efficacy and safety of three main types of rotavirus vaccine (bovine, human, and rhesus) for 21,070 children. Different levels of efficacy were demonstrated with different vaccines varying from 22 to 89% to prevent one episode of rotavirus diarrhoea, 11 to 44% to prevent one episode of all-cause diarrhoea, and 43 to 90% to prevent one episode of severe rotavirus diarrhoea. Rhesus vaccine demonstrated a similar efficacy against one episode of rotavirus diarrhoea (37 and 44% respectively), and one episode of all-cause diarrhoea (around 15%) for trials performed in high and middle-income countries. Results on mortality and safety of the vaccines were scarce and incomplete. We noticed important heterogeneity among the pooled studies and were unable to discard a biased estimation of effect.

REVIEWER'S CONCLUSIONS

Current evidence shows that rhesus rotavirus vaccines (particularly RRV-TV) and the human rotavirus vaccine 89-12 are efficacious in preventing diarrhoea caused by rotavirus and all-cause diarrhoea. Evidence about safety, and about mortality or prevention of severe outcomes, is scarce and inconclusive. Bovine rotavirus vaccines were also efficacious, but safety data are not available. Trials of new rotavirus vaccines will hopefully improve the evidence base. Randomized controlled trials should be performed simultaneously in high-, middle-, and low-income countries.

Expanding distribution of human serotype G6 rotaviruses in Australia

Serotype G6 rotaviruses are common pathogens of cattle but are rarely found in humans. In Australia, human G6 isolates have previously been detected in two major southern population centres. A new isolate, ASG6.02, was detected in central Australia (Alice Springs) in 1997. Comparison of the deduced amino acid sequence of the major neutralizing antigen, VP7, indicated that ASG6.02 was related to human G6 viruses isolated from children in Italy and Australia. Phylogenetic analysis supported the close relationship between ASG6.02 and other Australian isolates and indicated that G6 VP7 sequences generally clustered according to the species of origin (human, bovine or porcine). The VP4 type of ASG6.02 was determined as P-type [14], in common with other isolates from Australia and Italy. The detection of ASG6.02 indicates that the distribution of this serotype is increasing in this country and may have implications for successful vaccine development.

Rotavirus vaccines--an update

Rotavirus vaccines offer the best hope to reduce the toll of acute rotaviral gastroenteritis in both developed and developing countries. An association with intussusception (IS) led to the withdrawal of the first licensed rotavirus vaccine in the USA in 1999, forcing a re-evaluation of the safety profile of potentially lifesaving vaccines. Development of new rotavirus vaccine candidates has continued, with a bovine-human reassortant vaccine and an attenuated human monovalent vaccine commencing Phase III trials. Several other candidates are in early Phase I and II clinical trials. The creation of innovative funding strategies to support vaccine development and production, specifically in developing countries, aim to make vaccines available where rotavirus causes the greatest impact.

Generation and characterization of six single VP4 gene substitution reassortant rotavirus vaccine candidates: each bears a single human rotavirus VP4 gene encoding P serotype 1A[8] or 1B[4] and the remaining 10 genes of rhesus monkey rotavirus MMU18006 or bovine rotavirus UK

The global disease burden of rotavirus diarrhea in infants and young children has stimulated interest in the biological and clinical characteristics of these agents, leading to intensive efforts to develop a vaccine. A rhesus rotavirus (RRV)-based quadrivalent vaccine ("RotaShield") was licensed and administered to about 1 million infants and found to be highly effective. However, it was withdrawn because of a link with intussusception. This vaccine was developed according to a modified "Jennerian" approach in which one of the two major outer capsid proteins (VP7) shares neutralization specificity with one of the four epidemiologically important human rotavirus serotypes. The other outer capsid protein (VP4) is derived solely from RRV and is distinct from the VP4 of the four human rotavirus serotypes of epidemiologic importance. In an effort to further increase the immunogenicity of the existing VP7-based RRV quadrivalent vaccine, we generated three single VP4 gene substitution reassortant rotavirus candidate vaccines, each of which bears a single human rotavirus VP4 gene encoding P serotype 1A[8] or 1B[4] specificity while the remaining 10 genes are derived from the rhesus rotavirus. By incorporating one or two of these strains into the quadrivalent vaccine, a pentavalent or hexavalent RRV-based vaccine could be formulated thus providing antigenic coverage not only for VP7 serotype 1, 2, 3 and 4 but also for VP4 serotype 1A[8] or 1B[4], thus possibly augmenting its immunogenicity. Similarly, three single VP4 gene (P1A[8] or P1B[4]) substitution reassortants have also been generated in a background of 10 bovine (UK) rotavirus genes for addition to a second generation UK-based quadrivalent vaccine.