What is pneumonia?

  • Pneumonia is caused by infection from bacteria, viruses or fungi. Our lungs are made of lots of little air sacs (alveoli). Pneumonia causes these to become inflamed and fill with fluid.1
  • ​​​​The most common cause of community acquired pneumonia is a bacteria called Streptococcus pneumoniae.1
  • ​​​​​​It can be spread from person to person through physical contact, coughing and  sneezing.
  • Find out more information on how you can help protect your loved ones on the NHS website.2

Symptoms of pneumonia

While pneumonia can make you feel very unwell, symptoms vary and people often mistake it for cold and flu, not realising that they have pneumonia until they visit a healthcare professional.2

How do you catch pneumonia?

There are different types of pneumonia, with the two most common being bacteria and viruses. The various causes of pneumonia transmission, depending on the type, are listed below.

The two most common causes of pneumonia are bacterial and viral. Flu is one of the most common causes of viral pneumonia in adults, though post-flu complications can also cause bacterial pneumonia.3

Bacterial pneumonia causes4  


​​​​​​​Bacterial pneumonia is caused by different types of bacteria that works its way into the lungs and then multiply. Infections causing bacterial pneumonia can be spread through physical contact, coughing and sneezing.

  • The most common cause of bacterial pneumonia is a pneumococcal infection, due to bacteria called Streptococcus pneumoniae.
  • The second most common cause is from the bacteria Haemophilus influenzae. The bacterium may live in your upper respiratory tract, only causing harm with a weakened immune system
  • Other bacteria that can cause pneumonia include:
    • ​​​​​​​Staphylococcus aureus
    • Moraxella catarrhalis
    • Streptococcus pyogenes
    • Neisseria meningitidis 
    • Klebsiella pneumoniae

Viral pneumonia causes5

There are several viruses which can lead to viral pneumonia, including:

  • Adenoviruses, which can also cause the common cold and bronchitis5
  • Varicella zoster virus or chickenpox
  • Influenza virus, more commonly known as flu
  • Respiratory syncytial virus, which causes cold-like symptoms

Coughing, sneezing, or touching contaminated surfaces are common ways for viruses to spread.

Fungal pneumonia causes6

  • Fungal pneumonia usually refers to infections where the fungi invade lung tissue after entering the airways through inhalation6
  • Some species of fungi are more likely to cause pneumonia particularly in certain areas or among certain high-risk groups
  • Fungal pneumonia is rare in the UK and more likely to affect people with a weakened immune system2
  • There are several types of infections which can lead to fungal pneumonia, including7:
    • Aspergillosis, caused by aspergillus mould
    • Candidiasis, caused by candida fungus
    • Mucoymycosis, caused by mucor mould

Why is pneumonia so dangerous?

If you catch it, pneumonia can be serious and life threatening.8 

In 2019-2020, it is estimated that pneumonia was responsible for around 282,129 adult hospital admissions in England and approximately a fifth of hospitalised pneumonia cases were reported in people aged under 65.9

Studies have shown being hospitalised with pneumonia is a risk factor for heart attacks10 and bacterial pneumonia is linked with an increased incidence of stroke episodes in the week following infection​​​​​​​.11 

Pneumonia and influenza, combined, is one of the most common causes of death in the UK.12

Help protect against pneumococcal pneumonia

Find out how to help protect yourself or others against pneumococcal pneumonia.

View References
  1. BLF. What is Pneumonia. Available at: https://www.blf.org.uk/support-for-you/pneumonia/what-is-pneumonia/. Last accessed October 2021.
  2. NHS. Pneumonia. Available at: https://www.nhs.uk/conditions/pneumonia/. Last accessed October 2021.
  3. Rothberg MB., Haessler SD, Brown RB. Complications of viral influenza. Am J Med. 2008 Apr;121(4):258-64. doi: 10.1016/j.amjmed.2007.10.040.
  4. Healthline. Bacterial Pneumonia. Available at: https://www.healthline.com/health/bacterial-pneumonia#causes. Last accessed October 2021.
  5. Healthline. Viral Pneumonia. Available at: https://www.healthline.com/health/viral-pneumonia#causes. Last accessed October 2021.
  6. Healthhype. Fungal Pneumonia. Available at: https://www.healthhype.com/fungal-pneumonia-lung-infection-causes-symptoms-treatment.html#:~:text=Causes%20of%20Fungal%20Pneumonia%201%20Types.%20Some%20species,a%20similar%20effect%20and%20therefore%20increase%20the%20/. Last accessed October 2021.
  7. Patient. Fungal Lung Infections. Available at: https://patient.info/doctor/fungal-lung-infections. Last accessed October 2021.
  8. Healthline. Why pneumonia can be deadly for some people. Available at: https://www.healthline.com/health/pneumonia/can-you-die-from-pneumonia. Last accessed October 2021.
  9. NHS Digital. Hospital Admitted Patient Care Activity 2019/20: Diagnosis. Available at: https://digital.nhs.uk/data-and-information/publications/statistical/hospital-admitted-patient-care-activity/2019-20/ . Last accessed October 2021.
  10.  Corrales-Medina VF., Alvarez KN., Weissfeld LA., et al. Association between hospitalization for pneumonia and subsequent risk of cardiovascular disease. JAMA. 2015;313(3):264-74.
  11. Warren-Gash C., Blackburn R., Whitaker H., McMenamin J., Hayward AC. Laboratory-confirmed respiratory infections as triggers for acute myocardial infarction and stroke: a self-controlled case series analysis of national linked datasets from Scotland. European Respiratory Journal Mar 2018, 51 (3) 1701794; DOI: 10.1183/13993003.01794-2017.
  12. Office for National Statistics. Deaths registered in England and Wales. Deaths: underlying cause, sex age-group, 2018. Table 9: Leading causes of death by age-group, sex numbers and percentages, 2018. Available at: https://www.ons.gov.uk/file?uri=%2fpeoplepopulationandcommunity%2fbirthsdeathsandmarriages%2fdeaths%2fdatasets%2fdeathsregisteredinenglandandwalesseriesdrreferencetables%2f2018/referencetablesfinalv22.xlsx . Last accessed October 2021.
PP-VAC-GBR-1837 October 2021