Rotavirus vaccine studies in Europe

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.

Impact and effectiveness of RotaTeq® vaccine based on 3 years of surveillance following introduction of a rotavirus immunization program in Finland

BACKGROUND

Finland introduced universal rotavirus (RV) vaccination in September 2009, with exclusive use of the pentavalent human-bovine reassortant RV vaccine RotaTeq® and following a vaccination schedule at 2, 3 and 5 months of age. This study monitored the impact of RV vaccination on hospitalizations due to RV acute gastroenteritis (RVGE). The results following the first 3 RV seasons after implementation of universal RV vaccination are presented.

METHODS

Prospective hospital-based surveillance identified children with acute gastroenteritis admitted to 2 University Hospitals (Tampere and Oulu, Finland), from December 2009 to August 2012. The surveillance covered a population of approximately 173,000 children from the 2 hospitals' catchment areas. Stool samples were taken and analyzed centrally for RV by enzyme-linked immunosorbent assay, with genotyping by reverse transcription polymerase chain reaction. International Classification of Diseases discharge codes were collected retrospectively pre- and postvaccination.

RESULTS

During the 3-year prospective surveillance, 127 RVGE episodes were identified. Of these, 117 were in unvaccinated children and 6 were in fully vaccinated children (RotaTeq, n = 3; Rotarix, n = 3). The vaccine effectiveness against hospitalized RVGE for fully vaccinated children was 92.1% [95% confidence interval (CI): 50.0-98.7] among children eligible for the National Immunization Program. When analyzing retrospectively the Tampere and Oulu hospital databases for all children aged <16 years, hospitalizations for RVGE had decreased by 78% in the postvaccination period (2009-2012) compared with the prevaccination data (2001-2006).

CONCLUSIONS

Severe RVGE requiring hospitalization was virtually eliminated in vaccine-eligible children in the 3 years following implementation of universal RotaTeq vaccination in Finland.

Rotavirus vaccination: a concise review

Live attenuated oral rotavirus vaccines were tested for proof-of-concept in the early 1980s, the first vaccine (RotaShield, Wyeth) was introduced in 1998 but was subsequently withdrawn because of association with intussusception, and the two currently licensed vaccine (Rotarix, GlaxoSmithKline, and RotaTeq, Merck) were introduced in 2006. Before licensure both vaccines were extensively tested for safety (for intussusception) and efficacy in trials comprising in over 60,000 infants each. Rotarix is a single-strain human rotavirus vaccine (RV1) and RotaTeq is a combination of five bovine-human reassortant rotaviruses (RV5). Although the composition of the two vaccines is different, their field effectiveness and, largely, mechanism of action are similar. Both prevent effectively severe rotavirus gastroenteritis (RVGE) but are less efficacious against mild RVGE or rotavirus infection. Field effectiveness of these vaccines in Europe and the USA against severe RVGE has been above 90% and in Latin America around 80%. Trials in Africa have yielded efficacy rates between 50 and 80%. Rotavirus vaccination has been introduced into the national immunization programmes of about 20 countries in Latin America, with Brazil and Mexico as leading countries, as well as in the USA, Australia and South Africa. Introduction into other African countries will start in 2012. In Europe, Belgium, Luxembourg, Austria and Finland and five federal states of Germany have introduced universal rotavirus vaccination. The reasons for the slow progress in Europe include low mortality from RVGE, unfavourable cost-benefit calculations in some countries, and concerns that still exist over intussusception.

Clinical trials of rotavirus vaccines in Europe

Clinical trials of a live oral candidate rotavirus vaccine were started in 1982 and soon demonstrated that severe rotavirus disease can be prevented by vaccination. The first bovine candidate vaccine was withdrawn because of inconsistent efficacy, and studies of a rhesus rotavirus vaccine were initiated. A field trial of rhesus-human reassortant tetravalent rotavirus vaccine in Finland was pivotal for the licensure of this vaccine (RotaShield) in the United States in 1998. However, this vaccine was withdrawn in 1999 because of association with intussusception. Safety therefore became a major issue in the development of new candidate rotavirus vaccines. A pentavalent bovine-human reassortant rotavirus vaccine (RotaTeq) showed about 70% efficacy against any rotavirus disease and 100% efficacy against severe disease in Finland, according to the Clark scale. A large, multinational safety trial indicated no association of this vaccine with intussusception, and its licensure is under review in the EU. An attenuated human rotavirus vaccine (RIX4414; Rotarix) was developed from G1 rotavirus strain 89-12. A trial in Finland showed efficacy comparable with that of RotaShield, and a larger trial is under way in several European countries. In the first epidemic season, vaccine efficacy was 73% against any and 90% against severe rotavirus (mostly G1) gastroenteritis, according to the Vesikari scale. A large scale safety trial, conducted in Latin America plus Finland, indicated no increased risk of intussusception among recipients of Rotarix compared with placebo. The licensure of Rotarix is in process in the European Union.