Novel Oral Polio Virus Type 2 (nOPV2) Vaccine: The Global Eradication Initiative

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Highlights:

• During the year 2020-2022, circulating vaccine-derived polio virus (cVDPV2) was responsible for 97-99% of poliomyelitis cases, mainly in Africa
• Poliomyelitis continues to be a global threat due to reintroduction of poliovirus following dropping vaccination rates
• nOPV2 offers a novel solution to control and eradicate poliomyelitis from its grassroots level

Polio or poliomyelitis, is a life-threatening disease caused by the poliovirus. Infections caused by polio viruses result in acute flaccid paralysis in up to 1 in 200 infected individuals and death in 10 to 20 people per 200 cases (1^✔).

Northern India witnessed its last wild polio-virus type 2 case in the year 1999 and achieved the global certification of wild polio-virus (WPV) type 2 eradication in 2015. April 2016 witnessed the withdrawal of Type 2 containing oral polio vaccines from the routine immunization programme worldwide (tOPV-bOPV switch). This was done to prevent the rising incidence of circulating vaccine-derived polio-viruses (cVDPVs) caused by type 2 polio-virus. cVDP can occur when the weak strain of polio-virus contained in oral polio vaccine (OPV) circulates in communities for a long period of time and genetically reverts to a form that can cause paralysis.

‘As a part of the Polio eradication and endgame strategy, a more genetically stable novel OPV2 was developed against circulating vaccine derived polio virus (VDPV2) and granted World Health Organization Emergency Use Listing. #polioeradication#poliovaccine’

To maintain immunity levels to Wild Polio Virus 2, high-risk countries were encouraged to introduce Injectable Polio vaccine (IPV) into their routine immunization programs prior to making the switch. Today, four years after the global switch, there have been reports of increasing circulating vaccine-derived polio-virus type 2 (cVDPV2) outbreaks in parts of Africa, Southeast Asia, and the Middle East (2^✔).

Causes for cVDPV2 Outbreaks And Solutions Offered

The cVDPV 2 outbreaks are driven by several factors like:

• Declining immunity levels to the type 2 virus among children born after the vaccine switch
• Insufficient routine immunization coverage with type 2 containing Inactivated Polio Vaccine (IPV)
• Low-quality outbreak response campaigns with monovalent Sabin OPV2 (mOPV2), which was selected for responding to cVDPV2 outbreaks

In 2020, the Global Polio Eradication Initiative (GPEI) launched a new strategy for cVDPV2 outbreak response as part of the Polio Eradication and Endgame Strategy: The novel oral polio vaccine (nOPV2).

nOPV2: It's Role in The Battle Against Polio

• nOPV2 is the genetically modified version of OPV2
• It has been granted use under the Who Emergency Use Listing (EUL)
• In clinical trials, it has been seen to provide comparable protection against polio-virus
• It is genetically more stable, safer and less likely to be associated with the emergence of cVDPV2
• It has the potential to be a significant tool to help stop outbreaks more sustainably (3^✔)
• WHO's Strategic Advisory Group of Experts on immunization (SAGE) has recommended that countries with outbreaks of cVDPV2 urgently respond by prioritizing use of nOPV2 where possible
• As of May 2023, 43 countries have been verified to use nOPV2 in the event of a cVDPV2 outbreak (4^✔)
• nOPV2 is an oral vaccine and administered via two drops given into the mouth of the child, as with other oral polio vaccines
• nOPV2 is only recommended for outbreak response under EUL and can only be used as part of an outbreak response strategy
• nOPV for types 1 and 3 polio-virus, called nOPV1 and nOPV3, are in development and the first in-human trials were conducted in 2021.Currently there is no plan to replace bOPV in routine immunization programme with nOPV (5^✔)

nOPV2 is proving to be a critical tool for more sustainably stopping cVDPV2.

Along with nOPV2 however, the best way to stop these outbreaks remains ensuring rapid, high-quality outbreak response and maintaining strong disease surveillance.

References:

1. What is Polio? - (https:www.cdc.gov/polio/what-is-polio/index.htm)
2. Novel OPV2 (nOPV2) Management, Monitoring, Removal and Disposal (in 50 dose vials with VVM type 2) - (https:polioeradication.org/wp-content/uploads/2021/02/nOPV2-Vaccine-Handling-Technical-Guidance-20201103-ENG.pdf)
3. nOPV2 - (https:polioeradication.org/nopv2/)
4. cVDPV2 Outbreaks and the Type 2 Novel Oral Polio Vaccine (nOPV2) - (https:polioeradication.org/wp-content/uploads/2023/06/GPEI_nOPV2_Factsheet_31-May-2023.pdf)
5. nOPV2 Frequently Asked Questions (FAQ) - (https:polioeradication.org/wp-content/uploads/2022/10/nOPV2-FAQ-August-2022-EN.pdf)

Source: Medindia

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