- chronic (long-term) respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), emphysema or bronchitis, chronic heart disease, such as heart failure, chronic kidney disease, chronic liver disease, such as hepatitis
- chronic neurological conditions, such as Parkinson's disease, motor neurone disease, multiple sclerosis (MS), a learning disability or cerebral palsy
- diabetes, problems with your spleen - for example, sickle cell disease or if you have had your spleen removed
- a weakened immune system as the result of conditions such as HIV and AIDS, or medicines such as steroid tablets or chemotherapy
- being seriously overweight (a BMI of 40 or above)
- those who are pregnant