Oxford Martin School

On Thursday 26 November Dr Jodie McVernon, Deputy Head of the Vaccine and Immunisation Research Group at the Melbourne School of Population Health, Australia, gave the penultimate lecture in our seminar series on 'Getting to Zero'. She spoke on the subject of "Global Eradication of Infectious Diseases: can 'Not Very Much' undermine the goal of 'None at All'?" A podcast of this lecture is available here.

Dr McVernon began by highlighting the 'global burden' of disease. Between 14 and 17 million people die each year due to infectious diseases, accounting for about 25% of all deaths, and children are particularly vulnerable. Yet, despite the well-publicised success of global smallpox eradication, 'zero' remains an elusive goal for the majority of vaccine-preventable diseases.

So, why did vaccination work so well in the case of smallpox? Dr Mc Vernon argued that smallpox was a 'golden ticket', an unusually simple case which is unlikely to be repeated. In the case of smallpox, the disease was easily and quickly identifiable, the vaccination developed was able to bypass the infection stage - reducing the pool of susceptible individuals and, crucially, once people were vaccinated they retained immunity for life. This made it very hard for the virus to re-establish itself in an area where smallpox had previously been eradicated.

However, other diseases have proved to be more challenging. Polio, whooping cough and influenza (as well as their associated vaccinations) have very different characteristics to small pox, and eradication may not be realistic in these cases. Dr McVernon laid out some of the most problematic characteristics, arguing that these make 'getting to zero' difficult, if not impossible, for most infectious diseases:

• Many polio cases are asymptomatic, making it impossible to isolate infectious individuals; and similarly, whooping cough can be infectious for three weeks with patients not showing any symptoms at first.
• The whooping cough vaccine appears to be better at preventing disease than infection - simply preventing the transition from the asymptomatic to the symptomatic phase of the diseases. So, while fewer people are falling ill, the disease continues to circulate at the same rate.
• The polio vaccine continues to be shed for some time after vaccination and there have been reported cases of vaccine-derived polio cases where large amounts of the vaccine have infiltrated water supplies.
• In some cases, the immunity conferred by a vaccine does not last for life. For whooping cough, it lasts for just six years; with influenza, the pace of mutation necessitates a new round of seasonal vaccinations every year.
• There is some (disputed) evidence that those who receive seasonal flu vaccines are more vulnerable to outbreaks of pandemic flu.

Dr McVernon concluded that success in the case of smallpox may have raised unrealistic hopes about our ability to eradicate disease. However, while a global zero may not be a realistic target, there are other strategies which may help to reduce the 'global burden of disease' (the resultant number of deaths, and disabilities). Dr McVernon argued that, in most cases, efforts to reduce the circulation of disease or to protect of highly vulnerable populations, such as children and the elderly, could offer more achievable strategies than a global eradication campaign.

The discussion following the presentation touched on a wide range of issues. Questions included:

• What are the implications of a failed 'global zero' campaign in the context of disease control?
• Why was the SARS epidemic controlled, where swine flu was not?
• Given the huge cost of vaccination programmes, how much of a financial incentive is there to eradicate individual diseases?
• How much of a barrier do local superstitions pose to the eradication of polio?

We invite continued discussion and comments below.