WHO aims to reduce cases of vaccine-derived polioviruses through the replacement of trivalent oral poliovirus vaccine with bivalent vaccine and the implementation of inactivated poliovirus vaccine, according to a recent report in MMWR.
“The global withdrawal of trivalent oral poliovirus vaccine, specifically its type 2 component, will represent a substantial milestone in the effort to eradicate polio, because it will mark the eradication of wild poliovirus type 2 and, in the long term, should lead to the elimination of type 2 vaccine-derived polioviruses,” Lee M. Hampton, MD, MSc, medical officer at the CDC, and colleagues wrote.
The researchers also wrote that the introduction of inactivated poliovirus vaccine should result in widespread prevention of paralytic polio caused by wild or vaccine-derived type 2 polioviruses.
The use of oral poliovirus vaccines (OPV) that contain live poliovirus unintentionally can cause vaccine-derived polio, Hampton and colleagues wrote. This happens when the viruses used in the vaccine undergo genetic changes during intestinal replication. Although this occurrence is rare and happens in communities with low vaccination coverage, the researchers said it can possibly be prevented through vaccine-replacement strategies.
WHO’s strategy to reduce all cases of circulating type 2 vaccine-derived poliovirus will commence with a synchronized global switch in April 2016. It will involve swapping out trivalent vaccine — which contains live poliovirus types 1, 2 and 3 — for a new bivalent vaccine that contains only live poliovirus types 1 and 3. Type 2 was selected for removal because it was present in more than 97% of cases of circulating vaccine-derived poliovirus reported since 2006.
To reduce the risk for outbreaks, which could be caused by desynchronized implementation schedules in individual regions, WHO plans to introduce an injectable vaccine containing inactivated poliovirus. The investigators said this will help to alleviate cases of circulating type 2 vaccine-derived poliovirus due to lapsed coverage. WHO initiated this strategy in June, with 46% of WHO member states (n = 194) already using inactivated poliovirus vaccine.
“The global withdrawal of the type 2 component of OPV offers a valuable opportunity to develop and test measures for conducting such a withdrawal efficiently and safely, including measures related to vaccine procurement and stock management, which also will be needed during the eventual global withdrawal of all OPV after eradication of all wild polioviruses,” Hampton and colleagues wrote. – by David Costill
Disclosure: The researchers report no relevant financial disclosures.