EU Science Hub

Prevention is better than cure: targeted vaccination to halt epidemics

Mar 09 2018

Amidst growing concerns over the low uptake of flu shots in Europe, scientists from the Italian National Research Council and the JRC confirm that vaccinations remain the best way forward when it comes to stopping the spread of infectious diseases.

It's an option that is nearly always more effective than either doing nothing or attempting to contain an outbreak through quarantine.

Under normal circumstances, the most effective way to prevent illness is to vaccinate according to national immunisation schedules.

Widespread immunisation programmes in Europe have made previously deadly diseases such as smallpox and polio a thing of the past.

This study looked specifically at epidemic outbreaks.

The scientists ran physics-based simulations on networks which sought to replicate the way individuals interact with one another in the real world, such as through the global air transportation network.

The simulations are simplified versions of computational frameworks commonly used to investigate the global spread of real-world epidemics, such as Severe Acute Respiratory Syndrome (SARS).

Nevertheless, they help understand basic features of more complicated and realistic models.

In the simulations, individuals correspond to 'nodes' that can transmit an infection through the links between them.

The scientists found that quarantining nodes after the outbreak of an epidemic very quickly becomes ineffective.

Under the assumption that the ‘cost’ of quarantining a node is comparable to that of losing the node to infection (as in the case of, for example, plant outbreaks where quarantine involves the physical removal of the infected individuals), even the 'do nothing' (non-intervention) strategy becomes preferable to quarantine quite early on in a simulated outbreak.

Of course, these results do not apply to situations where the ‘cost’ of quarantine is much lower than that of losing nodes to infection as, for example, in the case of a deadly human pathogen.

Targeted vaccination was found to be the best option in nearly all epidemic cases. The scientists used a vaccination strategy based on 'optimal percolation', which consists of finding the least set of nodes that, when removed from a network, can fragment it into small clusters.

The idea behind this approach is that fragmenting the network ensures infections are contained within small groups, hence preventing the occurrence of large outbreaks.

This might all seem like common sense, but preventive vaccination is not common practice for all illnesses and for some, vaccines do not yet exist.

The norovirus outbreak at this year's Winter Olympic Games is an example of where quarantine has been used as the only option available to health officials.

Medical professionals attempted to contain the outbreak by imposing quarantine on the hundreds of staff who were unlucky enough to catch the virus. Despite these measures, the illness continued to spread and even started to affect some of the athletes.

In recent years, physicists have made significant advances in the field of network immunisation, developing increasingly efficient techniques to immunise a network by the 'removal' (vaccination) of a few nodes. This knowledge can help to support health policy as policymakers look to ensure increased global security against epidemics.