New studies assess vaccine wastage, polio resurgence risk in Bangladesh

Muhammad Nabil

Wastage of inactivated polio vaccines (IPV) in small outreach immunisation sessions remains a challenge to effective vaccine delivery in Bangladesh, indicates a new study with icddr,b.

Polio vaccines. Photo: JC McIlwaine / UN. CC BY-NC-ND 2.0

The newly introduced IPVs in routine immunisation schedules may be wasted due to packaging issues, as they come in 5-dose vials. If they are opened to deliver fewer than 5 doses, the left-over vaccine in the opened vial cannot be re-used and is wasted.

“The findings indicate that using a 2-dose fractional IPV (one-fifth of full IPV dose) can minimise the wastage and extend IPV immunisation to more children globally,” says Dr K Zaman, senior author of the study published in The Journal of Infectious Diseases, alongside collaborators from the Centres for Disease Control and Prevention (CDC), USA and the Ministry of Health and Family Welfare, Bangladesh.

The study authors have also published a second paper in The Journal of Infectious Diseases, examining cold-chain adaptability for IPV transport in Bangladesh. Their findings caution that IPVs might lose potency due to temperature fluctuations during transport.

“This can be a problem despite the fact that Bangladesh has substantial cold-chain storage and transportation capacity,” says Dr Zaman.

The study recommends close monitoring of cold chains during vaccine transportation to minimise waste.

Both studies were part of a supplemental issue on polio eradication in The Journal of Infectious Diseases, coordinated by the Task Force for Global Health, with support from the Bill and Melinda Gates Foundation and the CDC.

On this World Polio Day, Bangladesh celebrates three years of polio-free status as endorsed by the World Health Organization (WHO). icddr,b researchers had played a key role and continue to support research and drives for eradication of this infectious disease by conducting studies on polio vaccines in the country.

icddr,b senior scientist Dr K Zaman

 

Can polio come back? 

There are three types of naturally occurring poliovirus - type 1, 2 and 3. Trivalent oral polio vaccines (tOPV) target all three types, while bivalent oral polio vaccines (bOPV) target two types (type 1 & 3) and monovalent vaccines (mOPV) target only a single strain.

Following WHO recommendation as part of polio endgame strategy, the previously-used tOPV for mass immunisation was withdrawn because type 2 cases have not been reported since 1999 and because tOPV interferes with the immune response prompted against poliovirus type 1 and 3.

A child is being fed oral polio vaccine. Photo: GMB Akash / icddr,b

In April 2016 the tOPV was replaced with bOPV, combined with at least one dose of inactivated polio vaccines (IPVs). IPVs contain a ‘killed’ virus that is unable to revert to a harmful form. These were introduced worldwide to eliminate the risk of vaccine-derived poliovirus circulation, which in very rare cases can occur from oral polio vaccines (OPVs).

Resurgence of type 2 poliovirus could only occur from either wild type 2 poliovirus, which has been already eradicated, or from the Sabin 2 vaccine strain in the existing tOPVs – the phenomenon known as vaccine-derived poliovirus (VDPV). Withdrawal of tOPV was meant to stop any potential VDPV circulation from the type 2 strain.

WHO declared Bangladesh polio-free in 2014. Photo: icddr,b

OPVs are based on weakened versions of live poliovirus and are excreted by immunised children and passed on to others but do not cause disease.

“However, on very rare occasions, these might mutate genetically if left to circulate in areas with low vaccine coverage for a longer period of time,” says Dr K Zaman, one of the co-authors of a new study with icddr,b published in the Lancet Infectious Diseases, which aimed to assess whether the risk of community transmission of type 2 would be higher after withdrawing the tOPV.

The risks of community transmission of type 2 poliovirus may increase with time following tOPV withdrawal, suggests this new study with collaborators from the Institute for Disease Modelling, the University of Virginia, the University of California-Los Angeles and Gates Foundation.

However, transmission was not shown to increase in the community as a whole. “The findings provide useful insights for global interventions to eradicating polio,” adds Dr Zaman.

Poliovirus responsible for poliomyelitus. Photo: Alain Grillet / Sanofi Pasteur. CC BY-NC-ND 2.0

Disease caused by VDPV is rare, with only a few hundred cases reported worldwide. Nevertheless, it is a challenge to eradicating polio globally.

In case of any unexpected event, stockpiles of monovalent oral polio vaccine targeting type 2 poliovirus (mOPV2) are being maintained by UN agencies to respond to type 2 outbreaks resulting from tOPV withdrawal.

The authors conclude by saying that continued research into alternative polio vaccines that confer robust immunity to type 2 poliovirus without the risk of VDPV emergence will be vital to global polio eradication efforts, which aim for a polio-free world by 2018 as envisaged by the Global Polio Eradication Initiative

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