Fever, (a high temperature which usually develops suddenly)
Headache
Extreme tiredness
General aches and pains, particularly painful muscles and/or joints
Cough
Sore throat
Stuffy or runny nose
Stomach symptoms such as loss of appetite, nausea, vomiting, diarrhoea (more common in children than adults)
Healthy people who develop influenza will feel extremely unwell for a few days, but generally recover within a week or two. However, there is a risk that some people will develop life-threatening complications (such as pneumonia) so seasonal influenza can have far more serious consequences for the vulnerable.
This is why all outbreaks of influenza are taken seriously and why millions of people who are vulnerable to the complications of influenza are vaccinated against it every year.
Complications of influenza Anyone can get the flu (even healthy people), and serious problems from influenza can happen at any age. However, older people, people with chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and young children are more likely to be vulnerable to influenza complications.
The most common complications are bronchitis and pneumonia. Influenza can also make chronic health problems worse. For example, people with asthma may experience more or worse asthma attacks while they have the influenza and influenza may trigger a worsening of pre-existing chronic congestive heart failure.
As a result, outbreaks of influenza can result in deaths, largely amongst older people and those with less developed or less effective immune systems (the body’s natural defence system that fights infections).
Spread Influenza is very contagious, meaning that the virus spreads easily from person to person. It is spread mainly through coughing and sneezing, when tiny droplets containing virus particles enter the air and are breathed in by others. Influenza can also be spread by someone touching another person’s hand, or a surface that is contaminated with virus, and then touching their own nose or mouth.
Once the virus has entered via the nose or throat it takes between 1 and 4 days for the infected person to develop influenza symptoms. But a person can be infectious from the day before they develop symptoms until up to a week later.
Influenza spreads very quickly, particularly in crowded situations, such as certain public places, offices, schools or day-care centres.
The virus can survive outside the body for longer periods of time if the weather is cold and dry which is why seasonal epidemics appear in winter months.
Seasonal influenza epidemics The influenza outbreaks or epidemics that occur each year are known as ‘seasonal influenza’ and usually occur in the winter months in temperate climates. An epidemic is when more cases of an infectious disease occur than expected in a country or region. There are influenza outbreaks every year so the term ‘epidemic’ is generally used only for the more severe years.
Influenza viruses are constantly changing so it is typical for new strains to appear each year. It is not possible to predict with certainty which influenza viruses will predominate during a given season; they can change from one season to the next or they can even change within the course of a single influenza season. The timing of the start of the epidemic, its severity and how long it lasts will vary from year to year depending on the virus strain.
WHO estimates that 5 to15 % of the population is affected with infections of the chest and upper airways of the body during annual influenza epidemics. Every year there are 3 to 5 million cases of severe illness and between 250,000 and 500,000 deaths due to influenza around the world.
Immunity and vaccination When the body’s immune system (which fights viruses and bacteria) comes into contact with a virus it rapidly learns how to deal with it and develops ‘immunity’ to protect itself from getting the same infection in the future. It is possible to help the body to develop immunity to some influenza viruses before it is infected by them by being vaccinated. Also, as influenza viruses are often variations, or strains, of earlier viruses it is possible for your body to develop some general immunity as it comes into contact with more and more different influenza strains over the years.
People with weakened immune systems, for example older people and those with immune systems affected by other illnesses, can be most vulnerable. Young children, whose immune systems are not yet fully developed, are also more at risk of the complications of influenza. This is why these groups are prioritised in vaccination programmes.
Solvay and influenza vaccines Solvay has been making vaccines for almost 60 years and is one of the biggest producers of influenza vaccines in the world. Every year Solvay works with WHO and the health regulatory bodies around the world, to produce vaccines such as Influvac® that protect people from influenza. There is more information on Solvay’s Influenza website.
Pandemic influenza A pandemic is an outbreak of infectious disease that spreads through populations across a large region; for instance a continent, or even worldwide.
Pandemic influenza occurs when a new influenza virus develops which is so different to previous strains that people have little or no immunity to it. The virus is spread in the same way as normal flu; through the air by coughs and sneezes or by hand/face contact after touching a surface contaminated with the virus.
In a pandemic the symptoms could be more severe than ‘ordinary’ influenza and people of any age could be at risk of serious illness. There is more information in the Pandemic Influenza section.
Naming influenza viruses There are three types of influenza virus; A, B and C. The types differ in relation to the species they are able to infect. Types A and B are responsible for human disease.
Influenza virus particles have two proteins known as antigens on their outer surface that are important for the activity of the virus and that are used to differentiate between virus strains. These proteins are called haemagglutinin (H) and neuraminidase (N).
By identifying the virus type as well as the differences in the H and N proteins the specific virus can be defined e.g. influenza A (H1N1) is the recently emerged virus thought to have originated in pigs whilst influenza A (H5N1) is a bird influenza virus that has caused deaths in humans since 2003.
The influenza virus should not to be mixed up with Haemophilus influenza, a bacterium, long considered to be the cause of influenza, and which also causes respiratory illnesses. Bacterial infections are treated with antibiotics, not with anti-virals.
