What is vaccine-derived polio and what are the available vaccines against poliovirus?
- August 23, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
No Comments
What is vaccine-derived polio and what are the available vaccines against poliovirus?
Sub: Sci
Sec: Health
Context:
- A two-year-old child in Tikrikilla, Meghalaya has been infected with vaccine-derived polio.
- This is not a case of wild poliovirus, but an infection that presents in some people with low immunity, the Union Health Ministry said.
About Polio/Poliomyelitis:
- Polio is a viral infectious disease that affects the nervous system, potentially causing irreversible paralysis and even death.
- It mostly affects children under 5 years of age.
- Poliovirus is an RNA virus belonging to the Picornaviridae
- India received polio-free certification by the WHO in 2014, after three years of zero cases.
Types of polio virus:
- There are three variations of polio virus: Wild poliovirus type 1 (WPV1), Wild poliovirus type 2 (WPV2) and Wild poliovirus type 3 (WPV3)
- In 2019, WHO declared that WPV3 has been eradicated worldwide.
- However, more than 90% of vaccine-derived poliovirus outbreaks are due to the type 2 virus present in oral polio vaccines.
Transmission:
- Polio is transmitted from person to person through oral-faecal route or through contaminated food or water.
Vaccines for Polio:
- The first successful polio vaccine for poliovirus was made by Jonas Salk in 1950s.
- Salk inactivated the virus using formaldehyde and injected it into the muscles of test subjects. This inactivated polio vaccine (IPV) induced systemic immunity in the subjects.
- After Salk, Albert Sabin developed another vaccine that contained live polio strains, weakened by growing them serially in macaque cells, making them unfit for human infection.
- Since this vaccine contained the live virus, it had to be administered through its natural mode of infection – in this case, oral. This is what we today know as the OPV.
OPV vs IPV:
- OPV is usually preferred over IPV because of its ease of administration.
- The weakened virus in OPV can occasionally revert, causing the disease it is meant to prevent.
- IPV, on the other hand, is a less potent vaccine, but contains inactivated virus particles and hence no risk of causing vaccine-associated paralytic poliomyelitis (VAPP) – a rare, adverse reaction to OPV.
About Vaccine-derived polio:
- Vaccine-derived polio is a rare condition that occurs when the weakened (also called attenuated) strain of poliovirus used in the oral polio vaccine (OPV) mutates and regains the ability to cause paralysis.
How Vaccine-derived polio spreads:
- OPV contains a live, attenuated virus, which triggers an immune response when administered, thus protecting people from the disease.
- The attenuated virus replicates in the intestines for a limited period and is excreted in the stool.
- In rare cases, the virus can mutate enough to cause the disease again, and circulate in areas where either immunisation is low, or where immunocompromised persons reside, or regions with poor sanitation and hygiene.
Circulating Vaccine-derived polio virus:
- According to WHO, the virus is classified as “circulating” (cVDPV2) if it is detected in at least two different sources and at least two months apart, that are genetically linked, showing evidence of transmission in the community.