Did you know flu viruses can change regularly?
This makes it difficult for the human body to recognise it in the future. That is why the flu vaccine composition is reviewed every year with the aim of protecting you from the most common types of flu.
Usually, after a first infection, the immune system will remember the virus so that the body’s natural defence system responds rapidly to any future infection. This immune ‘memory’ also develops after vaccination which allows the immune system to become familiar with the virus without causing illness.
How are flu vaccines regularly updated?
Throughout the year,healthcare professionals collect flu virus samples from patients worldwide. World Health Organization (WHO) collaborating centres analyse and monitor the flu strains to check whether they have evolved since last year. This allows experts to decide on the composition of the new influenza vaccine for the upcoming flu season.
A range of factors are taken into account. For example, scientists pay close attention to flu viruses circulating in the southern hemisphere (June-July) to predict which viruses may dominate the northern hemisphere flu season (Jan-Feb). Laboratories study the genetics of the viruses to help to predict whether vaccines and antiviral medicines will work on them.
Scientists also expose laboratory animals (usually ferrets) to the flu viruses to be used in the vaccine and study the antibodies the animal creates in response. This process is called antigenic characterisation. A blood sample is taken from the animal and the antibodies are tested against flu viruses in a lab. Scientists observe how the animal’s antibodies recognise and bind to samples of the flu viruses which are currently making people sick.
When required, the vaccine is updated to improve the likelihood that it will be effective. This decision must be taken in time for manufacturers to make, check and distribute millions of doses of flu vaccine in time for autumn, before the next flu season starts. Manufacturers need to know which flu strains to include in the vaccine approximately seven months in advance.
How effective are flu vaccines?
The flu vaccine reduces the risk of flu-related illness by between 40% and 60%. The effectiveness of the annual vaccine mainly depends on how well it matches the viruses in circulation. If scientists correctly predict which strains are likely to dominate the coming flu season, the vaccine will be more effective. If an unexpected strain emerges and causes a high proportion of flu cases, vaccine effectiveness will be lower.
Even if it is a perfect match, the vaccine will not provide everyone with 100% protection. The flu vaccines that are currently available tend to work better against some strains than others.
In addition, age and the health of the person having the vaccine can affect how well it works. Flu vaccines reduce older people’s risk of hospitalisation or death due to influenza. However, as the immune system gets older, its response can weaken. This means older people’s bodies respond less well to natural infection. But it also means their response to vaccines is weaker.
Research is ongoing to improve the effectiveness of flu vaccines in people of all ages. In addition, several groups of scientists are working on ‘universal flu vaccines’ which would work against all flu viruses. This would mean the vaccine will not need to be updated every year and it would avoid the risk of a mismatch between the annual vaccine and the circulating flu viruses.
If you have not yet had your flu vaccine, contact your healthcare provider today and make an appointment to protect yourself and your family.