Wild poliovirus circulation among healthy children immunized with oral polio vaccine in Antananarivo, Madagascar

Interrupting wild poliovirus transmission using oral poliovirus vaccine: environmental surveillance in high-risks area of India

Global eradication of poliomyelitis has reached critical stage. Sabin Oral Poliovirus Vaccine (OPV) has been successful in three major regions of the world. In India eradication of poliomyelitis from states of Uttar Pradesh (UP) and Bihar has been difficult due to high population and low-socioeconomic standards of living. Acute flaccid paralysis (AFP) surveillance and intensive OPV rounds continues with the World Health Organization (WHO) operational strategies. Yet apparent lack of progress in reducing the number of wild cases has resulted in occasional impatience and frustration, even leading to questions about ultimate feasibility of global eradication using OPV. Lucknow in UP is in geographical area endemic for poliomyelitis and is surrounded by high-risk areas yet maintains a polio-free status since 2002. Environmental surveillance study was conducted (2004-2006) to authenticate the decline in the wild poliovirus (PV) cases in Lucknow. Sewage sample analyses were compared with stools of AFP patients and healthy children from same geographical area. Study reveals useful information on OPV circulation and proves important epidemiological tool to trust WHO's OPV immunization program. Genetic sequencing had detected silent wild PV-1 circulation of RCP1PGI (EU049849), RCP2PGI (EU049850), RCP3PGI (EU049851), and RCP4PGI (EU049852) in sewage waters. Properties of isolates from sewage reflected those of viruses excreted from human. This study provides valuable information and encouragement to AFP surveillance to maintain high levels of OPV immunization campaigns in the most difficult endemic region of India to interrupt the wild PV transmission.

Mass vaccination campaigns to eradicate poliomyelitis in Madagascar: oral poliovirus vaccine increased immunity of children who missed routine programme

To assess the impact of mass vaccination campaigns using oral poliovirus vaccine (OPV) in Madagascar, serum neutralizing antibodies and geometrical mean titres (GMTs) to poliovirus were measured among 472 children aged up to 59 months, before and after the mass campaign, regardless of their previous history of routine vaccination. In this study, overall coverage with three routine and two mass campaign OPV doses was 69.9 and 93.4%, respectively. Seroprevalences to all poliovirus types were significantly higher after the mass campaign among the children who were not vaccinated through routine programme: 67.5% vs. 90.2% (P < 0.001) for type 1; 66.7% vs. 95.1% (P < 0.001) for type 2; and 55.3% vs. 82.9% (P < 0.001) for type 3. Geometrical mean titres to all poliovirus types also significantly increased after the mass campaign among the same study group: 34.5 vs. 238.9 (P < 0.001) for type 1; 35.1 vs. 402.6 (P < 0.001) for type 2; and 13.3 vs. 92.6 (P < 0.001) for type 3. Post-mass campaign seroprevalences and GMTs for poliovirus, especially types 1 and 3, among children who received up to two routine and two mass campaign OPV doses were significantly higher than pre-mass campaign seroprevalences among children who received three routine OPV doses. Reasons for lack of adherence to the vaccination programme and the mass campaign are discussed. The findings strongly support the WHO strategy of conducting mass campaign in all endemic countries. However, as the mass campaign strategy now has been discontinued, it is crucial to increase the routine coverage and to improve acute flaccid paralysis surveillance in order to fulfil the goal of poliomyelitis eradication.

Poliomyelitis in Oman. I. The last outbreak?

Since 1988, the Sultanate of Oman has experienced three outbreaks of paralytic poliomyelitis. The last outbreak occurred in December 1993 and involved two children aged 10 months and 4 1/2 years. The children had received five and four doses, respectively, of trivalent oral polio vaccine (OPV) and lived in the same village. Serum neutralizing antibody tests suggested that paralytic polio in these children was due to poor antibody response to OPV. Wild poliovirus type 1 was isolated from both patients, as well as from seven of ten close contacts of the older child, and one of eight contacts of the younger child. All contacts had received three to six doses of OPV. Genomic sequence studies indicated that the virus isolates belonged to a genotypic group prevalent in southern and western Asia, but differed markedly from virus isolated during the 1988/89 outbreak, suggesting another importation of poliovirus. In response to the outbreak, supplementary immunization with OPV was given to children <6 years of age, initially in the affected district, and subsequently to children in the whole country. This study demonstrates that immunization with three to six doses of OPV did not prevent infection with wild poliovirus. In those children with sub-optimal response to OPV, infection resulted in paralytic poliomyelitis. The outbreak remained localized in one village, indicating that the outbreak control measures were effective.

Enterovirus surveillance of Italian healthy children

Surveillance of acute flaccid paralysis (AFP) is the golden strategy recommended by the WHO to verify the condition of polio eradication in a country. Because of the difficulty to detect all of the expected AFP cases and to reach the target incidence of 1/100,000 requested by WHO, the surveillance of enteroviruses in the population has been adopted by several countries as an important additional method to verify the absence of wild-poliovirus circulation. To complete the results of AFP surveillance set up in Italy in 1996, we have conducted a wild poliovirus surveillance by examining stool samples from 1551 healthy children aged less than 5 years, collected during the period January 1997 to January 1998. The children were from three cities (Parma, Rome and Bari) located in northern, central and southern Italy. Thirty-nine polioviruses, 72 non-polio enteroviruses and 50 enteric, nonentero (NE), viruses were isolated from stool specimens. Polioviruses identified were nine type 1, seven type 2 and twenty-three type 3. Characterization of isolates by both antigenic and molecular methods showed that all polioviruses were of vaccine origin. As expected, most polioviruses, especially types 2 and 3, presented retromutations known to be associated with loss of the Sabin attenuated phenotype. The results of this study support the data obtained from the active AFP surveillance conducted in Italy in the same period--on the absence of paralytic disease due to wild poliovirus--and altogether demonstrate the effectiveness of the vaccination program.