Surveillance is key to eliminating and preventing infectious diseases. Early detection offers the chance of rapid response, which can stop a handful of cases or a few clusters of illness from becoming something far worse.
Take polio. Surveillance underpins the current global eradication effort: without it, we wouldn't know where or how the virus circulates, as 90 per cent of cases have no symptoms, which makes it difficult to identify them. As a result of early detection, however, 99 per cent of cases have been eliminated, and the disease is cornered in only three endemic countries — down from at least 125 in 1988.
The 'Polio Eradication and Endgame Strategic Plan', a comprehensive road map launched by the Global Polio Eradication Initiative in May to end polio by 2018, sees surveillance as key to guide eradication activities, and sets out steps to scale it up globally.  Recent advances in surveillance technologies, together with new tools such as mobile phone self-reporting and improved genetic sequencing of viruses, mean that diseases can now be tracked better and faster than ever before.
A global surveillance system
The polio programme has continuously incorporated new innovations and their impact is tangible. The widespread introduction of the systematic testing of sewage over the last five years has allowed the WHO and national governments to identify poliovirus in the faeces of infected individuals who do not present any symptoms.
This has enabled pre-emptive mass vaccinations to be launched — as happened this year in Egypt and Israel — even without the onset of any paralytic cases.
More recent innovations are also being used. In Uganda, the government deployed mTrac, a text message-based platform that allows local health workers to report potential cases of polio and other diseases in real time using their mobile phones.
Then, the origin of any virus can be detected through genetic sequencing, enabling scientists to track transmission and improving the focus of emergency vaccination campaigns.
The analysis is sometimes carried out in US Centers for Disease Control and Prevention labs, but more and more often it is done in regional or local labs where, for instance, a Pakistani stool sample will be sent to a Pakistani lab and tested by a Pakistani scientist.
The value of these tools extends beyond polio. Increasingly, the polio surveillance system incorporates the tracking of other diseases, such as influenza and measles. The strategic plan aims to ensure that resources built for polio, including surveillance infrastructure, also have the greatest possible impact on other public health priorities.
Protecting against pandemics
Today's technology is just the beginning. The latest ideas in digital disease detection — or 'clues from the cloud' — are opening doors to detect and combat viruses even more effectively. For example, in October 2011, the American Public Health Association, HealthMap and the Skoll Global Threats Fund launched Flu Near You, a crowdsourced initiative to track flu activity in the United States that's now entering its third season and is open to all.
We caught a glimpse of what the future holds last month, when hundreds of innovators, epidemiologists and engineers convened at the 2nd International Conference on Digital Disease Detection to explore how technology is changing the game for epidemic intelligence gathering.
Crowdsourcing is emerging as a trend. For instance, the Ministry of Health in Singapore and the Aggeu Magalhães Research Centre of the Oswaldo Cruz Foundation in Brazil are aggregating social media posts to look for emerging outbreaks or new symptoms of diseases such as dengue fever and influenza.
One group at the Boston Children's Hospital in the United States helped to create MedWatcher, an online tool to monitor attitudes and complaints about medicines, vaccines and medical devices. And another group, InSTEDD (Innovative Support to Emergencies, Diseases and Disasters), is encouraging citizens in places such as Cambodia to use Verboice, an interactive voice response tool, to help report on a range of health conditions even faster.
The potential of these innovations seems endless. The opportunity to get local people to directly report on health conditions in their communities provides economies of scale not possible with the traditional 'feet-on-the-street' approach.
The final inch
Advances in surveillance equip us better than ever before to take on diseases, but they are not enough. They must be grounded in the political will to use them effectively.
In tackling polio’s final inch, we need the commitment and ability to act on the data that surveillance provides. Finishing the job requires a tremendous level of national and global coordination. We had many of the tools to eradicate smallpox for years, but it wasn't until the world committed to a unified global programme to detect the last case and vaccinate each child that we wiped out the disease in 1980.
We have an opportunity and the tools to do this again now with polio. The strategic plan is a detailed blueprint of activities required to eradicate the disease. With global commitment to implement it, we can finish the job by 2018.
The world must step up to the plate and demonstrate what's possible when scientists, engineers, governments, campaigners and innovators push boundaries and work together. If political commitment and funding keep pace with continued innovation, no disease is too great to tackle.
Larry Brilliant is president and CEO of the Skoll Global Threats Fund. He was previously vice-president of Google and executive director of Google.org and played a key role in the successful WHO smallpox eradication programme in India. You can follow him on Twitter @larrybrilliant.
Mark Smolinski is the director of Global Health Threats at the Skoll Global Threats Fund. He was previously the director of the Predict and Prevent Initiative at Google.org and led the development of a regional surveillance system linking Israel, Jordan and the Palestinian Authority while at the Nuclear Threat Initiative.