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Polio's Catch-22: The Vaccine That Saves Also Risks
28 Jan
Summary
- Oral polio vaccine has nearly eradicated wild polio, but a rare mutation poses a risk.
- Vaccine-derived polio cases now outnumber wild polio cases globally.
- A new, more stable oral vaccine shows promise but still carries some risk.
Decades of global efforts have brought polio to the brink of eradication, with wild poliovirus now confined to Afghanistan and Pakistan. This success is largely attributed to the oral polio vaccine (OPV), a cheap and easily administered liquid containing a weakened live virus. OPV not only protects individuals but also limits transmission in environments with poor sanitation. However, the live virus in OPV can, in rare instances, mutate and regain its virulence, leading to vaccine-derived poliovirus (cVDPV) outbreaks. Since 2016, over 4,000 cVDPV cases have been recorded, surpassing wild polio cases and posing a significant challenge to complete eradication. These outbreaks are particularly prevalent in areas with low vaccination coverage.
Developed nations have largely transitioned to an inactivated polio vaccine (IPV) injection, which is safe but does not prevent transmission. The transition away from OPV, however, has proven complex. A 2016 decision to remove the type 2 strain from OPV backfired, leading to significant outbreaks attributed to the continued circulation of the type 2 vaccine-derived strain. Scientists are now developing and testing a new, more stable OPV. Early results from trials, including those in Uganda, show it significantly reduces the emergence of new vaccine-derived strains while still providing protection. Despite this progress, a rare instance of a recombinant strain was detected, indicating that the 'catch-22' of polio eradication persists, highlighting the need for continued vigilance and high vaccination rates globally.
