Influenza or ‘flu’ is an infectious illness caused by the influenza virus. In most cases influenza is a benign illness but for elderly people, pregnant women and people with chronic diseases, the complications of flu can be dangerous. Vaccination remains the best way of preventing the complications of flu and hospitalisation.
Surveillance of influenza, a public health issue
The intensity and severity of influenza varies year on year and depends on:
- the viral strains in circulation
- the vulnerability and sensitivity of the population to these viruses.
As it is very contagious, influenza must be closely watched to assess whether it poses a danger for public health.
What does Sciensano do?
In 2006, the Interdepartmental Influenza Committee appointed Sciensano as the institution responsible for influenza surveillance activities in Belgium.
The influenza surveillance accommodates 3 services:
- the service Viral diseases of Sciensano, which is formally recognized as the National Reference Centre (NRC) for influenza virus and is part of the Global Influenza Surveillance and Response System of the WHO
- the Epidemiology of infectious diseases describes the development of influenza
- and the service Health services research.
These teams work together and manage a sentinel network of general practitioners, laboratories and hospitals.
The surveillance provides information on:
- the duration and intensity of the annual seasonal flu epidemic
- the circulating viruses
- the impact and severity of the annual seasonal flu epidemic
- the antiviral resistance
- the vaccine effectiveness.
Finally, the Vaccine and Blood Product Quality Department is the Belgian Official Medicines Control Laboratory (OMCL), which is responsible for the quality control of the influenza vaccines before they can be placed on the European market.
Describe the development of influenza
Every week a network of 150 general practitioners report to Sciensano the number of consultations for the influenza syndrome and for acute respiratory infections.
These clinical data are collected throughout the year.
Identify the viruses in circulation
During the flu season (from week 40 of one year to week 20 of the next year), a systematical virological surveillance of respiratory samples is organised.
Every week the sentinel network of general practitioners and hospitals send samples of respiratory secretions (swabs) collected from a selection of patients with the influenza syndrome to Sciensano’s National Reference Centre (NRC) for influenza virus.
The NRC for influenza virus analyses these samples to identify and characterise the different viruses in circulation responsible for the influenza. The reference laboratory also monitors whether resistance to the available antiviral medicines develops.
Assess the severity of the epidemic and its impact on the population
It is only after the epidemic has occurred that Sciensano can estimate its impact and severity.
According to the clinical data collected and the viruses detected by the hospital network, Sciensano also analyses the complications relating to the influenza.
By combining clinical and virological data, Sciensano monitors the effectiveness of the flu vaccine on an annual basis.
The epidemic threshold makes it possible to declare the onset of an epidemic. It specifies the number of consultations per 100,000 inhabitants per week following which it may be considered that there is an epidemic.
Every year the European Centre for Disease and Control (ECDC) calculates the epidemic threshold for each country and each region on the basis of the figures for the previous 5 years.
According to the Moving Epidemic Method the curves are divided into three periods: pre-epidemic, epidemic and post-epidemic.
By comparing the epidemic periods for each curve, Sciensano determines the start of an epidemic according to the number of visits per week to the doctor for the influenza syndrome and on the basis of the percentage of samples testing positive for influenza virus.
Control of vaccines for influenza
Sciensano is the Belgian Official Medicines Control Laboratory (OMCL) and is responsible for the quality control of the influenza vaccines before they can be placed on the European market. This control is carried out by the OMCL, independently of the vaccine manufacturer and for each batch separately. This control consists on the one hand of a critical review of the production data and quality analyses carried out by the vaccine manufacturer and on the other hand of additional analyses carried out by an OMCL. Thus, the Vaccine and Blood Product Quality Department performs various laboratory analyses according to the European Official Control Authority Batch Release (OCABR) guidelines. In addition, the Department also checks whether the production and quality data of the vaccine manufacturer are in conformity with the specifications as approved and recorded in the registration dossier. If a batch complies with all the quality criteria, the Department issues a certificate to the manufacturer, the so-called EU batch release certificate, and the vaccine may enter the European market.