Polio case clarified by Sechenov scientists
The outbreak in a Russian orphanage makes the researchers think about the efficacy of the polio vaccine.
Poliomyelitis does not seem to pose a threat to public health today — but it is a very wrong, deadly idea. The disease is with us, and any outbreak can lead to terrible consequences. Scientists from Sechenov University and several other research organisations have investigated a case of confirmed polio in an orphanage in Russia, analysed the risks, and suggested improvements in the strategy of vaccination and health surveillance. The study has been published in the journal Viruses.
The poliovirus has been alongside humanity for thousands of years and has taken its toll, claiming numerous lives and making the survivors suffer from the complications. These include muscle weakness that sometimes results in movement disability, and problems with breathing because of the paralysed diaphragm. In the 1940s and 1950s, during the polio epidemic, many patients required respiration assistance — and this was achieved by iron lungs. Although most patients could recover, some continued living with iron lung support for decades, even to the present day. The era of polio almost ended with the adoption of a worldwide vaccination programme, the Global Polio Eradication Initiative of the WHO. The programme was launched in 1988, becoming the largest international public health initiative in history, and practically eliminated the disease, with only 33 wild polio cases in 2018 compared to 350,000 wild polio cases in 1988. However, there is a growing concern over the spread of the wild type virus in countries and regions where people are increasingly against vaccination.
Today, most problems arise due to vaccines based on the live attenuated virus, such as the trivalent oral poliovirus vaccine (tOPV) derived from Sabin strains. It was the golden standard of the Global Polio Eradication Initiative, but later it turned out that tOPV could be dangerous: in extremely rare cases, tOPV can cause the formation of vaccine-derived polioviruses (VDPV) and vaccine-associated paralytic poliomyelitis (VAPP). Also, persons with primary immunodeficiency disorders can produce VDPV (iVDPV) because Sabin strains can multiply in their organisms for a long time. A poorly vaccinated population facilitates the formation of circulating VDPV (cVDPV).
The case of acute flaccid paralysis, a common manifestation of polio, was registered in July 2014 in a hospital in Syzran (Samara Oblast, Russia). The patient was a 13-month-old boy living in a specialised local orphanage. He had been admitted to the institution in May 2014 and never received a polio vaccine. Also, 26 children in this orphanage — of the total 54 — were not vaccinated at that time.
The patient had VDPV type 3, confirmed by the analysis of faecal samples. The case was classified as contact VAPP. VDPV type 3 was also detected in three out of seven investigated healthy contacts, and two of these three babies had previously received an inactivated polio vaccine (IPV). Serology studies showed that one child had antibodies only against serotype 3, and another was positive for all three polio serotypes. Genetic analysis demonstrated that the polioviruses in the patient and three healthy contacts contained numerous mutations distinguishing them from the Sabin 3 strain.
To prevent the spread of the disease, the researchers identified healthy contacts (52 children) and monitored their health using serum and faecal samples for routine tests. The babies received IPV, some of them — several doses. In October and November 2014, several months after the hospital case, all the children tested negative for the poliovirus, based on the faecal samples. However, serum analysis revealed four children with relatively high titres against poliovirus serotype 3.
The scientists who worked on this case suggest that Sabin 3 was the cause of this outbreak, and the weakened virus most likely evolved in one host over a long period. The genetic analysis showed that the viruses in four children were related but significantly different, supporting the theory of active circulation in the orphanage. It was not possible to identify the infection source, since the childcare institution used only IPV — not OPV with the live virus. Most likely, one of the children had contracted the virus in a previous home or medical facility.
The most challenging aspect of this outbreak is that some babies — who were not immunodeficient and received IPV at least twice — did not have immunity to two poliovirus serotypes. As the world is ceasing to use OPV, according to the WHO, immunisation against polio will only be carried out with at least two doses of trivalent IPV. However, the reported outbreak case shows that two IPV doses may not be enough.
This research was conducted by scientists from the Institute for Bionic Technologies and Engineering (Sechenov University), Belozersky Institute of Physico-Chemical Biology (Lomonosov Moscow State University), Chumakov Federal Scientific Centre for Research and Development of Immune and Biological Products (Moscow), and Federal Centre of Hygiene and Epidemiology at the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing (Rospotrebnadzor).
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