Injectable vaccine may hold the key

It was in May 1988 that the World Health Assembly, the governing body of the World Health Organisation (WHO), adopted a resolution setting out the goal of global polio eradication. The vision then was that such eradication would build on the achievements of the Expanded Programme of Immunisation, which the world health body had launched nearly a decade and half earlier to protect children with vaccines against diphtheria, whooping cough, tetanus, tuberculosis, polio and measles.

“In theory, global polio eradication was to be the crowning glory of EPI [Expanded Programme of Immunisation] but, in practice, it was distanced from it,” observed T. Jacob John, a virologist known for his work on polio immunisation, in an editorial in the journal Expert Reviews Vaccines in 2009.

In developing countries, the oral polio vaccine (OPV) became the weapon of choice that was deployed. OPV has obvious advantages, including being cheap and easily administered. It allowed mass campaigns to be held. Such campaigns were instrumental in ending polio transmission in India.

However, the oral vaccine, which is based on live but weakened strains of the poliovirus, suffers from a major drawback. The vaccine strains of the virus can revert to virulence as they replicate in the gut of a child. In very rare cases, the vaccine-derived polioviruses (VDPV) that result can cause polio. Some of those revertant viruses also gain the ability to spread to other children, becoming just as dangerous as naturally-occurring wild viruses.

The choice

The inactivated polio vaccine (IPV), which uses killed strains of the virus, does not have this problem. But it has hitherto been more expensive and must be given as an injection. Over the last two decades, more than 35 of the wealthier nations have switched to IPV.

In a policy article published in the journal Science in 1997, Vincent Racaniello, a professor of virology at Columbia University in the U.S., and his graduate student, Alan Dove, pointed out that elimination of both vaccine and wild strains of the virus “cannot occur if only OPV is used.” They suggested making a transition to IPV. In a response published in the same issue of the journal, WHO officials said such a switch was unnecessary.

But the WHO has been forced to rethink its position. VDPVs have been circulating in Africa for several years now. Last year, a VDPV strain that arose in Pakistan not only crippled children there but also affected children in neighbouring Afghanistan.

Last year, the World Health Assembly asked the WHO to take steps that would make the injectable vaccine more accessible and affordable. Subsequently, in November 2012, the WHO’s Strategic Advisory Group of Experts on Immunisation (SAGE), recommended that all countries introduce at least one dose of IPV in their routine immunisation programme.

If IPV has to reach every vulnerable child, then routine immunisation will have to be strengthened in India. Infant immunisation levels vary considerably across states. In Tamil Nadu, over 80 per cent of infants have received all basic childhood vaccines. Only 33 per cent of infants in Bihar and 23 per cent in Uttar Pradesh have been similarly immunised.

The Global Polio Eradication Initiative's draft strategic plan for 2013-2018 indicates that efforts to identify and remedy weaknesses in India’s routine immunisation programme have already started.

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Printable version | Jan 25, 2022 2:36:44 AM |

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