The 2010 outbreak of poliomyelitis in Tajikistan: epidemiology and lessons learnt

Abstract

A large outbreak of poliomyelitis, with 463 laboratoryconfirmed and 47 polio-compatible cases, took place in 2010 in Tajikistan. Phylogenetic analysis of the viral VP1 gene suggested a single importation of wild poliovirus type 1 from India in late 2009, its further circulation in Tajikistan and expansion into neighbouring countries, namely Kazakhstan, Russia, Turkmenistan and Uzbekistan. Whole-genome sequencing of 14 isolates revealed recombination events with enterovirus C with cross-overs within the P2 region. Viruses with one class of recombinant genomes co-circulated with the parental virus, and representatives of both caused paralytic poliomyelitis. Serological analysis of 327 sera from acute flaccid paralysis cases as well as from patients with other diagnoses and from healthy people demonstrated inadequate immunity against polio in the years preceding the outbreak. Evidence was obtained suggesting that vaccination against poliomyelitis, in rare cases, may not prevent the disease. Factors contributing to the peculiarities of this outbreak are discussed. The outbreak emphasises the necessity of continued vaccination against polio and the need, at least in risk areas, of quality control of this vaccination through well planned serological surveillance.

Robustness against serum neutralization of a poliovirus type 1 from a lethal epidemic of poliomyelitis in the Republic of Congo in 2010

“…Another example includes the reemergence of type 2 VDPVs as a cause of AFP in countries with suboptimal vaccination coverage such as in Nigeria (26). Finally, 13 of 463 laboratory-confirmed polio cases (2.8%) from the 2010 Tajikistan WPV1 outbreak occurred in apparently preimmunized individuals, confirming our observations (6). The more pronounced differences in the AgS2a of PV1-RC2010 compared with the WPV1s from the Tajikistan outbreak may have facilitated a higher fraction of poliomyelitis in preimmunized individuals in the ROC outbreak.…”

“…A strain isolated in 1965 (19), termed Bar65, was used because it was genetically as distinct from the vaccine strains Sabin-1 and Mahoney, as PV1-RC2010 (17.8/17.7% versus 18.0/17.8% genomic nucleotide sequence distance, respectively) and equally distinct from PV1-RC2010 (17.7%). The second WPV1 was isolated from the 2010 Tajikistan outbreak (6). This strain, termed Tajik, was selected because it was genetically more closely related to PV1-RC2010 with 11.7% genomic sequence distance than to Sabin-1 and Bar65 (18.6% and 18.4%, respectively).…”

“…This does not exclude inefficient immune protection as the necessary and most likely cause of the outbreak (5,9,28). However, it is intriguing that the ROC outbreak was associated with a much higher CFR than similar outbreaks in regions where WPV circulation had been interrupted and a pronounced incidence in adult patients occurred due to vaccination gaps, such as in Albania in 1996 (29), Namibia in 2000 (5) or Tajikistan in 2010 (6).…”

“…Of the 445 confirmed cases, 390 occurred in the city of Pointe Noire (5,8,9), with a CFR of 47% and a median age of 20 y for patients with paralytic disease (5,8,10,11). For comparison, the CFR in the 2010 Tajikistan outbreak was only about 6% and 44% of cases of acute flaccid paralysis (AFP) were observed in children below 5 y of age (6). It has been proposed that the severity of the ROC outbreak resulted from breaches in vaccination coverage in adults, combined with the underreporting of mild cases (11,12).…”

83 Seroprevalence of poliovirus antibodies among 7-month-old infants after 4 doses of oral polio vaccine in Sistan-va-Baluchestan, Islamic Republic of Iran

“…In addition, a reduced immunogenicity of PV3 when compared to PV1 and PV2 has been shown for inactivated poliovirus vaccine (20) and, based on the above-mentioned evidence, presumably the same might be true for live attenuated OPV3. The threat of infiltration of wild poliovirus into these areas and occurrence of outbreaks such the 2011 outbreak in China (2) or the 2008 outbreak in Tajikistan (21), is real and there should be measures to tackle this problem. Use of bivalent (containing serotypes 1 and 3 vaccine) and monovalent (containing only serotype 1 or 3) formulations might be the best solution for this.…”