What are the features of OPV and IPV?
Oral polio vaccine (OPV):
- A cheap, easy-to-administer vaccine taken orally, widely used in India to prevent the spread of polio.
- Stops the virus in the gut, preventing outbreaks in areas with poor sanitation.
- Very rarely, it can cause paralysis or mutate, but newer versions (like bivalent OPV) are safer.
Inactivated polio vaccine (IPV):
- A shot with a killed virus, used in countries like the U.S. and Europe.
- Safer, with no risk of causing polio, but more expensive and less effective at stopping the virus from spreading in high-risk areas.
- India switched to IPV in 2016 to align with global plans for a polio-free world.
Why does OPV carry a higher risk of mutation/reversion compared to IPV?
- OPV: Contains live-attenuated poliovirus. It replicates in the gut, inducing immunity but may rarely shed weakened virus into the environment. Mutations during replication can restore neurovirulence, causing VAPP or cVDPV in low-coverage settings.
- IPV: Uses inactivated (killed) poliovirus, incapable of replication or mutation. Administered intramuscularly, it triggers systemic immunity without gut replication, eliminating VAPP/VDPV risks.
Why use OPV initially?
OPV was chosen for its low cost ($0.10–$0.20 per dose) and ability to stop polio in crowded, unsanitary conditions with oral delivery and minimal need for trained staff and cold chain. It provides mucosal immunity and herd effect, which is effective in reducing wild polio cases.
IPV ($1–$3 per dose) was less practical for mass campaigns in developing nations, especially before 2016, when the supply of IPV was limited and logistics costs were high.
What is today´s use?
Most countries now use IPV, but OPV is still used in polio-hotspot areas like Afghanistan and Pakistan.
In India, safety reasons, which include concerns about VDPV, VAPP and NPAFP, drove the switch from OPV to IPV in 2016, and it was enabled by scientific progress.
Why does this matter?
The OPV campaign, supported by the Gates Foundation, helped India defeat polio, a disease that once paralyzed thousands of children yearly. While OPV has rare risks, its benefits have saved countless lives. Misleading claims can create fear and harm vaccination efforts. Understanding the science and context behind vaccine use is key. Always trust information from credible sources like the WHO or major medical journals.
