Health ministry confirms 19 vaccine-derived polio cases in Sudan
The Federal Ministry of Health (FMoH) on 7 September 2020, reported 19 confirmed cases of vaccine-derived poliovirus (cVDPV2) in 10 states (Blue Nile, East Darfur, Gedaref, Gezira, Kassala, Red Sea, River Nile, South Darfur, West Darfur, White Nile). The first case was reported in South Darfur on 7 March and notified on 12 March 2020. A total of 320 cases of Acute Flaccid Paralysis (AFP) have been reported, of which 247 cases (77 per cent) were discarded as non-polio AFP cases, 54 cases (17 per cent) are pending classification and 19 cases (7 per cent) were cVDPV2 positive.
On 9 August 2020, FMoH notified the World Health Organisation (WHO) of the detection of a vaccine-derived polio (cVDPV2) in the country and announced an outbreak. According to the notification, the virus is genetically linked with Chad. The initial investigation of the two first cases indicated these cases were linked to cVDPV2s from the CHA-NDJ-1 emergence group, which was first detected in October 2019 and is currently circulating in Chad and Cameroon, WHO said last week.
As the poliovirus types detected in Sudan and Chad are genetically linked indicating cross-border spread, Sudan and Chad are working together to synchronize activities to contain the outbreaks, the UN Children’s Agency (UNICEF) and WHO said.
AFP is a neurological condition characterized by weakness or paralysis and reduced muscle tone. The term acute flaccid paralysis (AFP) is often used to describe an instance with a sudden onset, as might be found with polio. AFP is the most common sign of acute polio and used for surveillance during polio outbreaks.
Routine vaccination coverage during 2020 has declined compared with 2019 because of programmatic issues and the impact of COVID-19 containment measures, according to FMoH. The immunization trend started to improve in June 2020 and accelerated routine vaccination started on 26 August 2020. The government is planning two rounds of national vaccination campaigns targeting 8.6 million children under five years of age to ensure they are protected against polio. The first round will start on 4 October and the second round will take place during the first week of November.
UNICEF and WHO will support the government’s response to the polio outbreak.
Sudan’s last reported wild poliovirus case was in March 2009 and the country was announced polio-free in 2015 by WHO. However, the country has been considered at high risk for importation of polioviruses for several years due to a decline in population immunity resulting from insecurity and conflict in certain areas.
According to WHO, polio is a highly infectious viral disease that largely affects children under 5 years of age. The virus is transmitted person-to-person mainly through the faecal-oral route or, less frequently, by a common vehicle (e.g. contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and cause paralysis.
As for the vaccine-derived poliovirus, it can occur in the following situations, WHO explains. Oral polio vaccine (OPV) contains an attenuated (weakened) vaccine-virus, activating an immune response in the body. When a child is immunized with OPV, the weakened vaccine-virus replicates in the intestine for a limited period, with the body developing immunity by building up antibodies. During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community (and this can offer protection to other children through ‘passive’ immunization), before eventually dying out.
On rare occasions, if a population is seriously under-immunised, an excreted vaccine-virus can continue to circulate for an extended period. The longer it is allowed to survive, the more genetic changes it undergoes. In very rare instances, the vaccine-virus can genetically change into a form that can paralyse – this is what is known as a circulating vaccine-derived poliovirus (cVDPV), according to WHO.