What is vaccine-derived polio?

Key
points

·      
Overview: The child
was diagnosed with acute flaccid paralysis at a hospital in Assam’s Goalpara.
Officials in the State’s West Garo Hills district are on high alert following
the confirmation of the case.

·      
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. OPV contains a live, attenuated virus that is used for
immunisation against the disease. This weakened virus triggers an immune
response when administered, thus protecting people from the disease.

·      
Types of
poliovirus: Polioviruses are enteroviruses that are transmitted
primarily by the faecal-oral route. Three types — wild poliovirus type 1
(WPV1), wild poliovirus type 2 (WPV2), and wild poliovirus type 3 (WPV3) — have
been known to exist. Symptomatically, all these strains are identical.

·      
Polio
vaccines: The first successful polio vaccine for poliovirus was made
by Jonas Salk in the early 1950s. Salk inactivated the virus using formaldehyde
and injected it into the muscles of test subjects. This inactivated polio
vaccine (IPV) induced systemic immunity (relating to the blood, brain, and all
other organ systems) in the subjects. Albert Sabin developed another vaccine
that contained live polio strains weakened by growing them serially in macaque
cells, making them unfit for human infection.

·      
OPV vs.
IPV: OPV is usually preferred over IPV because of its ease of
administration — it does not require syringes or medical training and is
inexpensive. However, 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 has no risk
of causing vaccine-associated paralytic poliomyelitis (VAPP) — a rare, adverse
reaction to OPV. IPV is comparatively tougher to manufacture, too, as it
contains a chemically inactivated virus.