Global prevalence of poliovirus type 2 declines after switch to bivalent vaccine

Since the global switch from the trivalent oral polio vaccine to the bivalent oral polio vaccine, fewer countries detected poliovirus type 2 in patient and environmental samples, according to a recent MMWR. Ousmane M. Diop, PhD, of WHO’s polio eradication department, and colleagues reported that there has been substantial progress against polio since the launch of the Global Polio Eradication Initiative (GPEI) in 1988. Only 37 cases of wild poliovirus type 1 were reported in 2016, which is the lowest annual count to date. Moreover, cases of wild poliovirus type 3 have not been reported since November 2012, and wild poliovirus type 2 (PV2) was declared eradicated in September 2015. Although this progress has been attributed to the wide use of live oral poliovirus vaccines (OPVs), there have been numerous outbreaks caused by vaccine-derived polioviruses (VDPVs), according to the researchers. In 2015, VDPV type 2 (VDPV2) outbreaks occurred in Nigeria, Pakistan, Guinea,...