Predominance of Rotavirus P[4]G2 in a Vaccinated Population, Brazil

We identified 21 rotaviruses in 129 patients with diarrhea in a Brazilian city with high rotavirus vaccine coverage. All rotaviruses were genotype P[4]G2 with 1 mixed infection with P[NT]G9. Although virus predominance could have occurred randomly, the vaccine may be less protective against P[4]G2. Prospective surveillance is urgently needed.

R otavirus causes severe diarrhea, illness, and death worldwide (1). Infection rates with rotavirus remain high despite improved sanitation, and vaccination is likely to be the best control strategy (2,3). Several candidate vaccines are being developed, 2 are already licensed (4,5) and at least 5 are being evaluated (2,6). The 2 licensed rotavirus vaccines are designed to provide protection against rotavirus gastroenteritis caused by the most common worldwide circulating rotavirus serotypes (2). These include G types G1, G2, G3, and G4 and P types P [4] and P [8] (on the basis of variability in the outer capsid proteins VP7 and VP4, respectively).
One of the currently licensed vaccines (Rotarix; Glax-oSmithKline, Rixensart, Belgium), a live, attenuated, human monovalent rotavirus P [8] (5), and immunologic pressure exerted by the vaccine may cause emergence of rotavirus genotypes that are not controlled by the vaccine. This possibility could change the pattern and distribution of the most prevalent rotavirus strains in the vaccinated population.
Because this is an unprecedented epidemiologic situation, we monitored the effect the vaccine might have on predominant genotypes. We describe rotavirus genotypes recovered from children with acute diarrhea in Aracaju, Sergipe, Brazil, after the widespread introduction of the vaccine.

The Study
Children with acute diarrhea who came to 2 public hospitals (Joao Alves Filho and Municipal da Zona Norte) and 3 health centers that provided health services to a population (Santa Maria) in Aracaju, Brazil, were enrolled from November 2006 to February 2007. Children who came to the hospitals were enrolled consecutively on specifi c days of the week by study health workers, and children who came to the health centers were visited at home after we checked the daily attendance lists of the centers. Acute diarrhea was defi ned as any episode <14 days duration with >3 watery stools per day. Background and clinical information were collected after obtaining parental consent, and stool samples were stored frozen in duplicate at -80°C until analyzed in Liverpool, UK. Information on rotavirus vaccination was obtained from parents and cross-checked against vaccination record cards. A child was considered vaccinated if 2 doses of the vaccine had been recorded on the vaccination card. Rotavirus detection, genotyping, electropherotyping, isolation of strains in cell culture, and sequencing were performed as described (7). Severity of diarrhea episodes was classifi ed according to a modifi ed Vesikari score (8). Data were analyzed by using descriptive statistics in Epi-Info 2002 (Centers for Disease Control and Prevention, Atlanta, GA, USA). The study protocol was reviewed and approved by the Ethics Committees of the Liverpool School of Tropical Medicine and the Federal University of Sergipe.

One child had a mixed infection with P[4]G2 and P[NT]G9.
Nineteen specimens had short electropherotype strains, 1 was positive but with an undefi ned pattern, and 1 had insuffi cient RNA to produce a pattern.

Conclusions
Sergipe has achieved relatively high rotavirus vaccine coverage (54%) since introduction of the vaccine in 2006, with 48,165 doses provided in Aracaju. The vaccine was well received by the local population, and as new eligible children continue to be vaccinated, it is likely that vaccination levels will reach the high coverage currently attained for oral polio vaccine (100%) (http://tabnet.datasus.gov. br/cgi/tabcgi.exe?idb2005/f13.def).
To our knowledge, this is the fi rst report from Brazil of 1 rotavirus genotype predominating in a population after introduction of a vaccine. The P[4]G2 strain is a genotype for which effectiveness of the vaccine appears to be lower. This genotype has been previously reported in Brazil but represents only 6.1% of all the genotypes published since 2000. The proportions of strains with P[4]G2 has ranged from 0% to 27% in various studies, and no study reported that this was the predominant strain. Our fi nding of 100% prevalence of this genotype is unusual. Limited evidence of the effectiveness of Rotarix vaccine against the P[4]G2 strain has been reported (9,10) because the VP4 and VP7 proteins are not found in the P [8]G1 strain that is included in this vaccine.
Although our numbers are small, a lower proportion of vaccinated children had rotavirus-associated diarrhea, which likely refl ects the protective effect of the vaccine. Four children were infected despite having been vaccinated and their infections were as severe as those in children who had not received the vaccine. This fi nding confi rms that the vaccine does not afford complete protection against infection. Although predominance of the P [4]G2 strain in this population could be due to random preponderance of this genotype and is unrelated to vaccine use, this epidemiologic fi nding highlights the need for postlicensure surveillance of the vaccinated population.