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What is a vaccine-derived poliovirus?

Topics Covered:  Issues related to Health.

What is a vaccine-derived poliovirus?

What to study?

For Prelims: Polio- symptoms, spread and prevention, vaccine- derived poliovirus?

For Mains: Recurrence- concerns and challenges, ways to address them.

Context: In the last one year or so, polio has made a comeback in countries such as the Philippines, Malaysia, Ghana, Myanmar, China, Cameroon, Indonesia and Iran, mostly as vaccine-derived polio infection. All these countries had wiped the virus out at various times during the last couple of decades.

What is a vaccine-derived poliovirus?

It is a strain of the weakened poliovirus that was initially included in oral polio vaccine (OPV) and that has changed over time and behaves more like the wild or naturally occurring virus.

This means it can be spread more easily to people who are unvaccinated against polio and who come in contact with the stool or respiratory secretions, such as from a sneeze, of an infected person. These viruses may cause illness, including paralysis.

How is it spread?

  1. Oral polio vaccine (OPV) contains an attenuated (weakened) vaccine-virus, activating an immune response in the body. When a child is immunized with OPV, the weakened vaccine-virus replicates in the intestine for a limited period, thereby developing immunity by building up antibodies.
  2. During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community (and this can offer protection to other children through ‘passive’ immunization), before eventually dying out.

What’s the issue here?

A circulating vaccine-derived poliovirus (cVDPV) occur when routine or supplementary immunization activities (SIAs) are poorly conducted and a population is left susceptible to poliovirus, whether from vaccine-derived or wild poliovirus. Hence, the problem is not with the vaccine itself, but low vaccination coverage. If a population is fully immunized, they will be protected against both vaccine-derived and wild polioviruses.

Where does India stand?

In January 2014, India was declared polio-free after three years on zero cases.

In 2018, there was a brief scare when some vials of the polio vaccine were found contaminated with the polio 2 virus that had been eradicated from the country in 1999. However, WHO quickly issued a statement saying that all vaccines used in the government programme in India were safe.

The last case due to wild poliovirus in the country was detected on January 13, 2011.

How should India be prepared?

It calls for heightened vigilance, in short. Some years ago, India introduced the injectable polio vaccine in the Universal Immunisation Programme. This was to reduce chances of vaccine-derived polio infection, which continues to happen in the country. If both wild and vaccine-derived polio infection are reduced to zero, it would mean there is no trace left of the virus anywhere in the world, except in controlled situations in laboratories for future contingencies.

What is Polio?

It is a highly infectious viral disease, which mainly affects young children. The virus is transmitted by person-to-person spread mainly through the faecal-oral route or, less frequently, by a common vehicle (e.g. contaminated water or food) and multiplies in the intestine, from where it can invade the nervous system and can cause paralysis.

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Sources: Indian Express.