The article explains the concept of vaccine-derived poliovirus (VDPV), a rare but significant issue arising from the use of oral polio vaccines (OPV). The OPV contains weakened strains of poliovirus that, in very rare cases, can mutate and revert to a form capable of causing paralysis. This reversion usually occurs in areas with low immunization coverage, poor sanitation, or where immunity levels are low.

The article highlights a case from Meghalaya, India, where a two-year-old child was diagnosed with vaccine-derived polio. The child exhibited symptoms of paralysis, which were later confirmed to be due to the vaccine-derived virus. This incident has raised concerns, especially in regions where immunization is not widespread or sanitation is inadequate.

Key points:

1.     Types of Polioviruses: There are three types of polioviruses—wild poliovirus types 1, 2, and 3. Type 2 and type 3 have been eradicated globally, but type 1 still exists.

2.     VDPV and Immunization: The World Health Organization (WHO) classifies VDPV based on its detection in at least two different sources within two months, showing genetic links and evidence of transmission.

3.     Oral Polio Vaccine (OPV) vs. Inactivated Polio Vaccine (IPV): OPV is commonly used due to its ease of administration and low cost. However, it carries a small risk of reverting to a form that can cause polio. IPV, which uses inactivated virus, is safer but more expensive and harder to administer.

4.     Recent Developments: India has shifted from the trivalent OPV to a bivalent version to reduce the risk of vaccine-derived poliovirus. However, outbreaks of type 2 VDPV have continued, leading to increased vigilance.

The case in Meghalaya underscores the importance of maintaining high vaccination coverage and improving sanitation to prevent the re-emergence of polio, even in its vaccine-derived form.