A two-year-old child from Meghalaya has tested positive for polio, a viral disease that can lead to severe paralysis and even be fatal. The Health Ministry has clarified that this case is due to a vaccine-derived poliovirus and has assured that there is no need for undue alarm.
Vaccine-Derived Poliovirus
- Nature of the Virus: The virus involved is a vaccine-derived strain, which originates from the weakened form of the poliovirus used in oral polio drops.
- Vaccine Safety: The oral polio vaccine is generally safe and has been effective in eradicating polio in most countries. However, in rare instances, it can cause polio in children with weakened immune systems.
Mechanism of Vaccine-Derived Polio
- Virus Circulation: The weakened virus used in the vaccine can sometimes continue to circulate and mutate. It can regain its ability to cause severe infections if it is transmitted from child to child or if it causes chronic infections in children with weakened immune systems.
- Control Measures: In the recent Meghalaya case, the virus seems to have replicated in a single child. Efforts are being made to control the spread, particularly since most other children in the area are fully immunized.
Historical Context
- Past Cases: India’s last case of wild poliovirus was detected in Howrah, West Bengal in 2011. The country was declared polio-free in 2014. However, vaccine-derived polio cases have occurred since then.
- Notable Incidents: Examples include an 11-month-old child in Beed, Maharashtra in 2013 and a 2.5-year-old in Delhi. Vaccine-derived poliovirus was also detected in sewage samples in Kolkata in 2022.
Vaccine Types and Strategies
- Types of Polio Virus: There are three types of poliovirus, and weakened forms of these viruses are used in the oral polio vaccine.
- Vaccine Transition: In 2016, the vaccine was switched from trivalent (covering all three types) to bivalent (covering only types 1 and 3) due to the global eradication of type 2 wild poliovirus.
IPV vs. OPV
- Inactivated Polio Vaccine (IPV): IPV does not cause polio and protects against infection but does not prevent transmission. It is used in countries like Canada and the US.
- Oral Polio Vaccine (OPV): OPV is still used in India up to the age of five years, alongside IPV in routine immunization.
Multiple-Choice Questions (MCQs):
- What type of polio virus was detected in the Meghalaya child?
- A) Wild poliovirus
- B) Vaccine-derived poliovirus
- C) Type 1 poliovirus
- D) Type 3 poliovirus
- When was India declared polio-free?
- A) 2011
- B) 2013
- C) 2014
- D) 2016
- What is a major characteristic of IPV?
- A) It prevents both infection and transmission
- B) It causes polio in rare cases
- C) It protects against infection but not transmission
- D) It is used only in emergency situations
- Which type of poliovirus was eradicated globally by 1999?
- A) Type 1
- B) Type 2
- C) Type 3
- D) All three types
- What are the current polio vaccination practices in India?
- A) Only IPV is used
- B) Only OPV is used
- C) Both IPV and OPV are used
- D) No vaccination is used