Underlying principles of influenza surveillance

Underlying principles of influenza surveillance for pandemic preparedness

The PPHSN Influenza Specialist Group was established at the EpiNet regional workshop in September 2003. SPC’s PHS&CDC Section has been actively involved in the group, with an ADB consultant working on influenza preparedness.

With the epidemic of avian flu in birds in Asia, and the growing evidence of an increasing number of people becoming infected by the virus, the probability of a new influenza pandemic is increasing too. Therefore, as a timely and logical move, WHO organised a Consultation on Priority Public Health Interventions before and during influenza pandemic, in Geneva 16–18 March 2004.

In this consultation on priority public health interventions before and during an influenza pandemic, four working groups were organised:

  1. Surveillance for pandemic preparedness
  2. Public health interventions
  3. Antivirals – Their use and availability
  4. Better vaccines – Better access

SPC’s Epidemiologist was invited by WHO to take part in discussions related to influenza surveillance. The group on surveillance for pandemic preparedness highlighted in a series of important principles.

  • In many tropical and/or developing countries, more information is needed on the real burden of influenza during both the pandemic and inter-pandemic phases before allocating meagre existing resources to the control of this disease.
  • It was recognised that trying to detect the early emergence of a new influenza virus with pandemic potential during the inter-pandemic phase, is equivalent to “looking for a needle in a haystack”.
  • Influenza surveillance must be integrated into existing CD surveillance systems (e.g. SARS or outbreak surveillance). It is important to avoid unnecessary duplication, and reinforce these systems. As always, surveillance must be action-oriented, and the use of existing resources strategically balanced between surveillance (especially its sensitivity) and response.
  • Emphasis must be given to inter (or pre)-pandemic surveillance: inter-pandemic influenza surveillance is far more important than surveillance during the pandemic phase, as this is the period when early detection of the new strain could lead to public health measures delaying or maybe even preventing the spread of the pandemic. Inter-pandemic surveillance of influenza will also help with monitoring during the pandemic.
  • Because clusters of unusual cases can reveal the circulation of a new virus, and as early detection of inter-human transmission is critical (especially when it becomes sustained), the aim of this inter-pandemic influenza surveillance is the early detection and investigation of clusters of cases due to a new or unusual influenza virus with potential inter-human transmission. International transparency in reporting investigation results is crucial, as is international collaboration.
  • In the case of influenza, animal health impacts human health and a pandemic may arise from mixing and a reassortment of human and animal influenza viruses. Surveillance efforts must therefore integrate animal and human health information. Information sharing between animal and human health surveillance systems is important.
  • The planning of surveillance and response activities must include a risk assessment of the local or regional emergence of a pandemic virus, and the activities should be organised in a stratified way.
  • The disruption of essential services (including health) must be avoided as much as possible, until such disruption is unavoidable to properly face the pandemic.

Surveillance would also be supported by reliable and affordable rapid diagnostic tests that can detect influenza virus subtypes.

The surveillance group worked on surveillance objectives, indicators and methods by (inter-pandemic phase). This work was continued after the meeting, and the outputs will be available once finalised.

The outputs from the other groups will also be communicated with the report of the consultation. Vaccines may clearly take time to develop and will very likely be first available in those countries that can afford them. Similarly, antivirals are expensive and of limited availability as well as efficacy. Public health measures in general should realistically aim at slowing down the epidemic spread so that public services are not too disrupted, and healthcare systems can focus on complicated cases and avoid unnecessary fatalities.

Compiled by Dr Tom Kiedrzynski