Susceptibility to flu

Please note: Your Personal DNA Reports show genetic 'susceptibility' to traits, but not a direct relationship. As the majority of traits are influenced by environmental and lifestyle factors as well as your genes, you may find that not every result reflects your lived experience.

The probability that you or your friends are going to get the flu depends on three main things; pre-existing conditions and age, exposure, and your genes. 

Your genetics control two important factors that directly play a role in whether you are more likely to catch flu than average:

• Molecular messengers (called cytokines) that regulate how your body responds to and clears the flu. 

• Elements that help confine and prevent risk factors for severe flu (from the complement immune system).

While this report will focus on how genes affect susceptibility to flu, we will also take a look at non-genetic factors too. 

During a flu outbreak, individuals aged 65 year and above are 4.5 times more likely to catch the virus [1] Jump to reference section: [1] .  Infants and individuals with underlying conditions such as asthma are also at increased risk. This is because these factors are associated with a weaker immune system, which makes it easier for the virus to cause illness.

Specifically, viruses that cause flu (influenza) attack the respiratory system by multiplying within the air tracts and lungs [2] Jump to reference section: [2] . The resulting changes in the cells cause the symptoms of influenza infection. In addition, exposure to infected crowds and enclosed public transport spaces  also increases your chances of catching flu. 

How genes can influence flu susceptibility

Studies report that even with similar exposure, age or underlying conditions, some people are more likely to be infected with flu than others [3] Jump to reference section: [3] . This difference is because of changes in genes that control susceptibility to flu infection in some people. Researchers have found genetic associations with susceptibility to flu in two common types of human influenza viruses, H1N1 and H3N2. 

Which genetic variants might make me more susceptible to H1N1 influenza?

A number of studies have suggested that variant rs2564978 on the CD55 gene correlated with an increased risk of severe influenza infection [4] Jump to reference section: [4] . A normally functioning CD55 gene’s job is to prevent and reduce the strength of infections that may arise due to risk factors such as underlying diseases. Having the T form (allele) of variant rs2564978 increases susceptibility to severe flu infection, while the C form is associated with a lower risk than average [4] Jump to reference section: [4] . 

Which genetic variants might make me more susceptible to H3N2 influenza?

Molecular messengers in the body known as cytokines regulate how we respond to influenza infection. Overproduction of cytokines may increase the risk of flu infection to above normal levels [5] Jump to reference section: [5] as this overproduction can cause the body to damage its own tissues and infected organs, making it even harder to evade the flu. Over and underproduction of these cytokine messengers is partly caused by changes in genes controlling the process. Variant rs2275913 of the IL-17 gene has been confirmed by researchers to have such effects, with the G allele associated with increased influenza susceptibility risk [7] Jump to reference section: [7] . 

On the other hand, variant rs16944 of the IL-1ß gene may also be protective and reduce the risk of flu infection, studies suggest.

The IL-1ß gene and its corresponding cytokine are responsible for how the body responds to potential viruses. Overproduction of the IL-1ß cytokine, activated as a protective mechanism in the presence of a potential virus, has the potential to increase cell damage in individuals who already have a compromised immune system due to existing health conditions. However, in individuals with the rs16944 variant, the production of IL-1ß is regulated, limiting any damage that may further weaken the immune system.

The rs16944 (G) variant of the IL-1ß gene has been associated with increased protection against flu infection compared to the A variant, which is associated with an average risk of catching flu [5] Jump to reference section: [5] . 

The IL-28 gene has been labeled an ‘antivirus’ because it specifically functions to protect the body against infection by viruses [6] Jump to reference section: [6] . The resulting messenger of the gene is located on tissue surfaces that are close to harmful external environments such as lung linings. Variant rs8099917 results in changes in this function, with the G allele associated with a reduced risk of flu infection and the T allele an increased risk of flu infection [8] Jump to reference section: [8] . 

What other non-genetic reasons may make someone more susceptible to flu? 

The flu season and your genes are not the only reasons that may make you more susceptible to flu infection. Having a weakened immune system due to chronic diseases and exposure to the virus in crowded and confined places may increase your susceptibility to catching flu. Children also have less effectively developed adaptive immune systems and are more susceptible to repeated flu infections. Finally, smoking increases the likelihood of other lung-related infections that compromise the immune system, thus increasing susceptibility to flu infection [9] Jump to reference section: [9] . 

What can you do about it?

You can reduce your susceptibility to flu infection through preventive measures and treatment. In a case where you have already caught the flu, your immune system typically clears the symptoms in around two weeks. To shorten this period, you can use physician prescribed antiviral drugs which help your immune system reduce the severity of the symptoms.

Prevention practices are considered the best approach to manage flu susceptibility. First, prioritise washing your hands with soap and water or rub them with alcohol based sanitisers after having contact with people and public surfaces. You can also disinfect commonly handled items such as doorknobs  and light switches. Secondly, minimise contact with crowds and people with the flu during this season. Additionally, avoid sharing cutlery with others without cleaning the utensils first. Finally, maintain a healthy lifestyle and diet to ensure your immune system is healthy. This may involve reducing stress levels, exercising and minimising practices such as smoking [10] Jump to reference section: [10] .