Vaccine-Derived Poliovirus (VDPV) has emerged as an unexpected but significant challenge in the journey to eradicate polio worldwide. Unlike the wild poliovirus, VDPV originates from the oral polio vaccine (OPV) and has the potential to spread in communities, especially where immunization coverage is low. This feature explores what VDPV is, how it differs from wild poliovirus, and why addressing it is critical in the final push toward a polio-free world.

What Is Vaccine-Derived Poliovirus?

Vaccine-Derived Poliovirus is a mutated strain of the weakened virus contained in the oral polio vaccine (OPV). The OPV, an oral vaccine containing a live attenuated (weakened) virus, is effective in creating immunity against polio and is widely used in many countries because it’s cost-effective and easy to administer. In most cases, OPV stops circulating without causing any harm, immunizing those who take it and helping to protect those around them. However, in rare cases, the attenuated virus can mutate and regain strength, eventually behaving like the wild poliovirus and leading to outbreaks of poliomyelitis in under-immunized communities.

How VDPV Arises?

The mutation process typically occurs when the weakened virus from the OPV multiplies in a child’s gut and is excreted. In communities with high vaccination coverage, the virus typically cannot circulate further, making mutation unlikely. However, in areas with low vaccination rates, the virus can pass from person to person and eventually mutate. After many transmissions, it can revert to a form that causes paralysis, known as circulating vaccine-derived poliovirus (cVDPV).

There are three types of VDPV based on how they circulate and spread:
Circulating VDPV (cVDPV): The most concerning type, cVDPV occurs when VDPV spreads through a community. Outbreaks of cVDPV can happen if enough people are susceptible.

Immunodeficiency-Related VDPV (iVDPV): In people with immune deficiencies, the weakened virus may continue replicating in the gut, potentially evolving into a dangerous form.

Ambiguous VDPV (aVDPV): Cases of VDPV that do not fit into the other two categories.

How Serious Is the Threat of VDPV?

In recent years, cVDPV cases have increased, particularly in regions where polio eradication efforts have been challenged by conflict, displacement, or low health infrastructure. Sub-Saharan Africa, parts of the Middle East, and Southeast Asia have seen rising cases due to both low OPV coverage and disruptions in immunization efforts.

For example, countries like Afghanistan and Pakistan, where political instability hampers routine immunizations, have experienced both wild poliovirus and cVDPV outbreaks. Even in places like Syria and Yemen, cVDPV has caused significant outbreaks due to disruptions in vaccination during ongoing conflicts.

Steps Taken to Address VDPV Outbreaks

To combat cVDPV, the Global Polio Eradication Initiative (GPEI) has adopted several measures, including the following:

Switching to Inactivated Polio Vaccine (IPV): IPV contains killed virus particles and does not pose any risk of VDPV. However, IPV does not provide the same level of community immunity as OPV, so it is often used in combination with targeted OPV campaigns.

Development of New OPV (nOPV2): Scientists have developed a new version of the oral polio vaccine, nOPV2, designed to be less likely to mutate into a virulent form. The vaccine is now being rolled out in certain high-risk areas as part of a broader effort to control cVDPV.

Improving Routine Immunization Coverage: Increasing vaccination coverage remains the cornerstone of eliminating VDPV. Public health organizations and governments are working to strengthen immunization programs to prevent both wild poliovirus and cVDPV.

Rapid Response to Outbreaks: When cases of cVDPV are detected, rapid immunization campaigns are conducted to stop the spread. These campaigns target all children in the area, regardless of prior immunization status, to quickly establish immunity across the population.

The Role of Public Awareness and Community Involvement

The success of polio eradication, especially in combatting cVDPV, relies heavily on community trust and awareness. In regions where misinformation about vaccines is common, health agencies are working to provide clear information about the safety and necessity of polio vaccines. Community leaders, healthcare workers, and local organizations play a critical role in dispelling myths, addressing hesitancy, and encouraging vaccination.

Moving Forward: The Path to Global Polio Eradication

The rise of vaccine-derived cases has posed a challenge, but the global fight against polio remains strong. Efforts to transition to IPV, the development of nOPV, and rapid outbreak response measures are positive steps in controlling cVDPV outbreaks. However, until all regions reach and maintain high immunization coverage, the risk of VDPV will persist.

Polio eradication is within reach, but it requires ongoing global collaboration, innovation, and community involvement to address challenges like vaccine-derived poliovirus. By investing in robust immunization infrastructure, supporting outbreak response, and continuing community engagement, the world can move closer to achieving a polio-free future.