A Summary by Savannah Sanders
Image By The CDC and Authors: Mbaeyi C, Alleman MM, Ehrhardt D, et al.
Update on Vaccines-Derived Poliovirus Outbreaks- Democratic Republic of the Congo and the Horn of Africa, 2017-2018
In the Democratic Republic of the Congo and Horn of Africa, a great number of the citizens do not have access to the use of the live attenuated Sabin oral poliovirus vaccine (OPV). Transmission of Sabin poliovirus can go from person to person, which can cause genetic reversion, neurovirulence, and paralytic vaccine deprived poliovirus disease (VDPV). In the Democratic Republic of Congo outbreaks of VDPV type two (cVDPV2) have been reported, and Somalia has reports of VDPV type 3 (cVDPV3) in 2017-2018. 42 total cases of cVDPV2 in the DRC with the most recent reported case on October 7, 2018. In Somalia, samples of sewage detected cVDPV3 before any reports of the disease in humans. A total of 12 type 2 and type 3 cases of cVDPV have been found in humans in Somalia, with the most recent case on September 7, 2018. It will be a challenge of interrupting the spread of this disease because of the population of children alone, which is over 300,000. More time for surveillance is needed before anyone tries to stop the cVDPV virus.
When polioviruses replicate during transmission nucleotides substitute at 1.1% and accumulate in the genome. This can determine how long that particle strain has been circulating. VDPV are considered circulating when transmissions of the disease are genetically linked and is isolated from paralytic cases, community contact, and environmental sample, such as sewage.
The trivalent OPV (tOPV) vaccine contained the vaccine for type 1, 2 and 3 immunization. The portion the vaccine that prevented type 2 VDPV was responsible for 90% of the cases of VDPV in 2006-2015. After the declaration of eradication of wild poliovirus type 2 in 2015, the vaccine was globally changed to just type 1 and 3 Bivalent OPV (bOPV). The bOPV vaccine has inactivated poliovirus vaccine (IPV) and includes a single dose of all three poliovirus stereotypes instead of live sample of the poliovirus. This has been used for routine immunization and is used to lower the risk of people contracting type 2. However, a vaccine monovalent type 2 OPV is held in stock for a backup in case of a outbreak of type 2 since the switch occurred.
cVDPV2 outbreaks have been seen recently in the DRC. Two cases have been recorded in Maniema province, four cases in Haut Lomami, 11 cases in Mongala province, and two cases in Katanga province. When investigating each one of these cases, they found that there was a difference in nucleotides compared to the Sabin 2. Remember, this indicates the length of time the virus has been circulating. In Haut Lomami, the nucleotides has a difference of 15 different nucleotides, indicating that the virus as been circulating for over a year. An additional 26 cases where genetically associated with these outbreaks.
The Horn of Africa has outbreaks of cVDPV2 and cVDPV3. Samples of those virus was found in sewage collected from Banadir province and Somalia in October of 2017 and January 2018. The two samples where genetically linked together and again linked with another sample taken in two different sites in April 2018. This indicated that this particular strain of the VDPV has been circulating for over 3 years, with a difference of 36-44 nucleotides for cVDPV2 and over 1 year with 15-16 different nucleotides for cVDPV3.
Because of very low immunizations for children in both countries, during 2005-2013, multiple outbreaks of cVDPV2 occurred. Since then, tOPV where annually given. Then the switch to bOPV happened. The continue of outbreaks in 2017-2018 shows that children where not effectively prevented from the strains of cVDPV2 with the use of tOPV vaccine and cVDPV3 after the switch to bOPV. In places such as Mozambique, Niger, Nigeria and Syria, recent outbreaks have occurred in 2017-2018. This indicated that still a population of people are not getting vaccinated. It will take some time before all areas of this county receive the VDPV preventing vaccines.
Image By The CDC and Authors: Mbaeyi C, Alleman MM, Ehrhardt D, et al.
Mbaeyi C, Alleman MM, Ehrhardt D, et al. Update on Vaccine-Derived Poliovirus Outbreaks — Democratic Republic of the Congo and Horn of Africa, 2017–2018. MMWR Morb Mortal Wkly Rep 2019;68:225–230. DOI: http://dx.doi.org/10.15585/mmwr.mm6809a2.
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