Research helps optimise outbreak response

In 2010, high-profile and devastating outbreaks occurred in a number of previously polio-free countries, including new outbreaks in the Republic of Congo and Tajikistan. These outbreaks resulted in significant tragic humanitarian consequences, and have been associated with a high level of disease burden and - in particular in the case of the Republic of Congo - with an apparent unusually high case fatality rate (upwards of 40%). These two outbreaks are a real reminder of how dangerous this disease is, and underscores the urgent need to rapidly interrupt wild poliovirus transmission everywhere. With most of the world polio-free, there is a very real danger of new groups of susceptible population cohorts emerging, and should they be exposed to re-infection, would result in a higher likelihood of devastating consequences. To minimise the risk of outbreaks from importations, countries should maintain high population immunity levels, however the only way to truly address this is by removing the risk of importations from occurring by successfully interrupting the remaining chains of transmission.

These outbreaks also provide critical new insight into the importance of ensuring appropriate strategies are in place for the post-eradication era, and of the need to further optimise outbreak response activities. International outbreak response standards endorsed by the World Health Assembly (WHA) in 2006 (Resolution WHA59.1) significantly reduced the consequences (duration, geographic extent and associated cases) of new outbreaks since then, but focus must be on optimising outbreak response, be it associated with wild polioviruses or circulating vaccine-derived polioviruses (cVDPVs). Research is playing a critical role in this.

To help predict high-risk areas for outbreaks, mathematical modelling is aiding to classify areas at risk of both an importation and subsequent outbreaks, to help prioritise resources to highest-risk countries. New outbreak response tactics that have already shown promising field results will be clinically evaluated. A planned clinical trial will help determine the degree to which population immunity in outbreak settings may be more rapidly enhanced through application of the Short Interval Additional Dose (SIAD) strategy. This strategy exploits the availability of monovalent OPVs to shorten the interval between large-scale supplementary immunization activities (SIAs) in selected high-risk or infected areas, more rapidly building immunity. Serologic surveys can help determine impact of outbreak response and validate programme performance indicators. This tactic is providing crucial evidence on population immunity achieved as a result of outbreak response activities in Tajikistan last year. Further monitoring of outbreak response activities include the newly-evaluated Lot Quality Assurance Sampling (LQAS), to more definitively ascertain the level of vaccination coverage that is being achieved.

At the same time, ongoing transmission of the 2009 outbreak in Kenya detected in 2010 in Uganda underscores the urgent need to fill sub-national surveillance gaps for acute flaccid paralysis (AFP). Targeted surveillance reviews will now more readily identify any sub-national gaps, to enable operational teams to fill any identified gaps.

These activities will provide invaluable insight into optimizing outbreak response, and may potentially lead to a revision of internationally-agreed outbreak response guidelines. The newly-formed Independent Monitoring Board (IMB - see page 1) will monitor whether ongoing and any eventual new outbreaks are on track to being stopped in an epidemiologically-appropriate timeframe.