cVDPV

Circulating vaccine-derived polio virus or cVDPV are outbreaks of polio that are actually caused by the polio vaccine.

Very rarely, the attenuated (weakened) virus in the oral polio vaccine can revert to a form that can cause the person who was vaccinated or their close contact to actually develop polio.

It should not be confused with VAPP or vaccine-associated paralytic polio. With VAPP, the original strain of attenuated vaccine virus reverts to a form that can cause polio, but it does spread from one person to another, so does not lead to outbreaks.

cVDPV Outbreaks

Fortunately, both VAPP and cVDPV are rare.

How rare? VAPP only occurs in about 1 in every 1.27 million children receiving their first dose of OPV.

“Episodes of circulating vaccine-derived poliovirus are rare. Over the past ten years – a period during which more than 10 billion doses of oral polio vaccine were given worldwide – cVDPV outbreaks resulted in fewer than 800 cases cases (data updated weekly). In the same period, in the absence of vaccination with OPV, more than 6.5 million children would have been paralysed by wild poliovirus.”

Vaccine-Derived Polioviruses

And according to the WHO, there had only been a few dozen outbreaks of cVDPV over the past 10 years. Tragically, this has resulted in about 800 cases of paralytic polio in just over 30 countries.

A mass polio vaccination campaign will help combat an outbreak of vaccine-derived polio in Sudan - their first in 10 years.
A mass polio vaccination campaign will help combat an outbreak of vaccine-derived polio in Sudan – their first in 10 years.

A new outbreak of cVDPV in Sudan adds to those numbers though.

“On 9 August 2020, the Federal Ministry of Health, Sudan notified WHO of the detection of a circulating vaccine-derived poliovirus type 2 (cVDPV2) in the country. According to the notification, the virus is genetically-linked with Chad (sequencing results showed 12 to 19 nucleotide changes). Two Acute Flaccid Paralysis (AFP) cases were notified. The first case, a child of 48 months, had onset of paralysis on 7 March 2020 and was from Sulbi city of Kas locality in South Darfur state.”

Circulating vaccine-derived poliovirus type 2 – Sudan

This adds to the 172 cVDPV cases in 14 countries across the African continent have been reported in 2020.

Circulating Vaccine-Derived Polio Virus

Fortunately, just like wild type polio, we can stop cVDPV by increasing vaccination rates and increasing access to improved sanitation facilities.

Why?

Although anti-vaccine folks routinely cry wolf about shedding, the oral polio vaccine really does shed – in the stool of people who have been recently vaccinated. You can then be exposed to the attenuated polio vaccine virus (which can help give immunity to others in the community by passive immunization) or a strain of cVDPV (which can, unfortunately, help give others, especially if they are not vaccinated, paralytic polio) if they are exposed to open sewage or can not practice proper hygiene, etc.

Can’t we just stop using the live, oral polio vaccine?

Although a serious side effect of the vaccine, the vaccine’s benefits clearly outweigh the risk of both VAPP and cVDPV while polio is endemic (lots of cases) in a region, after all, without the vaccine, hundreds of thousands of children would get polio and would be paralyzed.

In polio-free countries, the risks of VAPP and cVDPV becomes greater than the risk of polio though, and they move to the inactivated polio vaccine. That helps prevent a situation in which the polio vaccines actually causes more cases of polio than wild type polio viruses.

Eventually, all countries will move to the IPV vaccine as we move closer to polio eradication. We came one step closer to that point in April 2016 when all countries that were still using the oral polio vaccine switched from trivalent OPV (three strains) to bivalent OPV (two strains) for their routine immunization programs. This could eliminate up to 90% of cases of cVDPV (most are caused by the type-2 strain which is not in bOPV)!

What To Know About cVDPV

Circulating vaccine-derived polio virus outbreaks are a rare side effect of the oral polio vaccine.

More Information About cVDPV

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