cVDPV remains a menace to the end game of polio eradication as it is one of the main causes of re-emerging polio apart from vaccination refusal. cVDPV originates from the oral polio vaccine. This weakened virus is excreted by the body through feces which could spread easily in a non-sanitary environment. In the early 2000s, in order to avoid the risk of cVDPV posed by the weakened poliovirus transmitted through oral polio vaccine (OPV), inactivated polio vaccine (IPV) was strongly advocated. By June 2018, 39 of 47 African countries had changed from OPV to IPV. In spite of that, sporadic cases of cVDPVs were spotted in countries using OPV with low population immunity [5]. For example, in 2018, cVDPV outbreaks were reported in Nigeria, Kenya and the Democratic Republic of the Congo,
Another approach to totally eliminate the risk of reemergence of wild poliovirus type-2, is to utilize bivalent OPV that contains Sabin serotypes 1 and 3 strains, instead of trivalent OPV that contains Sabin strains of all three poliovirus serotypes [6].{Regional Committee for Africa (68), 2018 #6} Drastic measures were taken when all member states in the WHO African Region withdrew trivalent OPV in May 2016 [5]. In Southeast Asia, Brunei and Malaysia has fully utilized the IPV but the trivalent OPV is still used in the Philippines and Indonesia with the latter introducing IPV in the national immunization program from July 2016 [7]. Furthermore, the use of monovalent type-2 polio vaccine in response to cVDPV Type-2 outbreaks poses the risk of the emergence of “de-novo” cVDPV Type-2 [8].
Besides the use of IPV or bivalent OPV, a comprehensive vaccine coverage is essential. Even though in general Brunei and Malaysia had achieved more than 95% immunization rates, approximately 12% of the children living in the affected sites on the coastal region of Sabah were not vaccinated, putting the whole community at risk of losing the vital herd immunity. The situation is heterogenous as across the South China Sea, the immunization rate among 105 million residents in the Philippines stood at 66 and 41% for OPV and IPV, respectively [9]. In the remote Papua province of Indonesia, polio vaccination coverage was 68.2% in 2017 and 40.8% in 2018 [10].
Cross-border polio vaccinations: the urgent need in southeast Asian countries
Cross border cooperation and efforts are needed. The mapping of less accessible border areas e.g. in Papua New Guinea and Timor Leste as well as migrant routes is important. The vaccination should be given by humanitarian groups to stateless children or non-citizens. It is especially important to maintain coverage of polio immunization at over 95% in high-risk areas with seasonal migrant populations. Surveillance of vaccination patterns based on data mining and geo-mapping of migrant and cross-border vaccinations that has proven successful in containing polio in Nigeria could be adopted to optimize the limited vaccine stocks and healthcare resources.