Why do we Need a New Flu Jab Every Year?

The Influenza virus is unique in that its structure changes. This has proved Influenza to be difficult to control through vaccination. Scientists have been trying to develop a universal influenza vaccine for many years.

Vaccines, in general, work by introducing your body to a weak, controlled or inactive sample of a pathogen to best prepare the body for recognising and fighting it in the future through the body’s memory cells. Future encounters with the same pathogen are often short and asymptomatic.

The surfaces of viruses are covered in molecules, usually proteins, called antigens. These help the body’s immune system recognise the disease as foreign and trigger an immune response to counteract it.

However, Influenza has a unique property concerning its antigens: antigenic variability. Through a combination of gene mutations (antigenic drift) and gene reassortment (antigenic shift), the antigens change structure to the point that they are unrecognisable by the body.

This nullifies any previous resistance gained by vaccinations or past infections. Now a future immune response (e.g. antibody production) will usually be slower, and symptoms might take effect, so you might notice the typical flu symptoms; fever, cough, sore throat and a runny nose.

Efforts towards producing a universal vaccine now have been focusing on the parts of the virus which do not mutate, called epitopes. Prof Arnon from the Weizmann Institute of Science has initiated the development of an epitope-based universal vaccine which has already been validated in early clinical trials to induce broad immunity against pandemic and seasonal strains. However, testing still needs to take place to develop this.

So, each year, as early as January, work is begun for a new seasonal vaccine for Influenza. 6 months later, around 500 million doses are produced and brought on the market in over 100 countries.


Milad Rouf Final Year Medical Student, Cardiff University.

Centers for Disease Control and Prevention. 2020. How Flu Viruses Can Change. [online] Available at: [Accessed 30 July 2020].

Centers for Disease Control and Prevention. 2020. Types Of Influenza Viruses. [online] Available at: [Accessed: 30 July 2020].

Chen, J., Deng, Y. 2009. Influenza virus antigenic variation, host antibody production and new approach to control epidemics. Virol J 6(30), https://doi.org/10.1186/1743-422X-6-30

Gottlieb, T., Ben-Yedidia, T. 2014. Epitope-based approaches to a universal influenza vaccine. Journal of Autoimmunity, 54, pp. 15-20.