Facts about Flu

Influenza is a serious infection with unexpected, severe consequences.

  • Flu or influenza is a highly contagious disease. Anyone can catch and spread it within their community.

  • Everyone is at risk of influenza, as the disease spreads easily through coughing, sneezing or talking.[1]

  • There are four main types of flu viruses with multiple sub-types that can infect people. Each season it’s difficult to predict exactly which subtypes of the viruses will dominate, their severity, and the full impact on public health.

  • Influenza can affect anyone, young or old and seriously disrupt lives, economies and societies. It accounts for a significant part of the annual economic burden of vaccine-preventable diseases across Asia.[2]

  • In healthy people of any age, the impact of influenza is unpredictable and can lead to serious consequences such as pneumonia, heart attacks, and stroke.[3]

  • Each year, 3 to 5 million cases of severe flu are reported worldwide.[4]

  • In vulnerable populations such as people living with diabetes, asthma, chronic heart or lung diseases, influenza causes higher rates of clinic visits, hospitalisations and deaths.[5]

  • Immediately following a flu infection, the risk of heart attack is elevated six times[v] and that of pneumonia by up to 100-fold.[6],[7]

  • Age increases susceptibility to infection, putting older adults most at risk for flu infection and serious complications.[8]

  • People with diabetes are 3 to 6 times more likely to be hospitalised due to influenza[9],[10], because the flu can make it harder to control blood sugar.[11]

  • Children have a high influenza transmission risk and the highest risks of severe complications are in children younger than 2 years old.[12]

Public health guidelines recommend annual influenza vaccination for high-risk groups.

  • The World Health Organization urges member states to reach a minimum 75% influenza vaccine coverage among high-risk groups[13] – including people aged 65 and more, pregnant women, people living with diabetes, asthma, chronic heart and lung diseases, children aged 6 months to 5 years, and healthcare workers.[14]

  • The US Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months old and older should get an influenza vaccine every season.[15]

  • In the new 2019-2030 Global Influenza Strategy, the WHO recognises the value of flu prevention in the fight against other global health threats, including non-communicable diseases and antibiotic resistance.[16]

Annual influenza vaccination is the most effective way to protect against flu infection and its complications.[17]​

  • Safe and effective vaccines are available and have been used for more than 80 years to help prevent the flu and reduce the risks of its severe consequences.

  • When healthy adults get vaccinated, it may provide herd immunity, helping to protect more at-risk populations.[18]

  • At current levels in Asia, we are far from achieving the World Health Organisation’s target of annual flu vaccination[19] for high-risk groups.

  • The World Health Organization recommends influenza vaccination for vulnerable populations such as health workers and older adults as a priority target group, to protect them against flu infection and related complications during the current COVID-19 pandemic.[20],[21]


Find out more about Influenza and reducing its burden through vaccination.

> World Health Organization. Health topics Immunisation. Facts about Immunisation

> World Health Organization Fact sheet Influenza (seasonal)

> World Health Organization. Vaccines against influenza WHO position paper – November 2012.

World Health Organization. Seasonal influenza FAQ.

> US Centers for Disease Control and Prevention (CDC). Key facts about Influenza.



[1] Centers for Disease Control and Prevention (CDC). (2018). How flu spreads. Retrieved from: https://www.cdc.gov/flu/about/disease/spread.htm

[2] De Francisco N., Donadel M., Jit M., et al. (2015). A systematic review of the social and economic burden of influenza in low- and middle-income countries. Vaccine; 33: 6537–6544. Retrieved from: https://www.sciencedirect.com/science/article/pii/S0264410X15014954?via%3Dihub

[3] Centers For Disease Control and Prevention. People at High Risk for Flu Complications. Available at www.cdc.gov/flu/highrisk/index.htm. Last accessed November 2019.

[4] World Health Organization (WHO). (2018). Influenza (Seasonal). Retrieved from: https://www.who.int/en/news-room/fact-sheets/detail/influenza-(seasonal)  

[5] Kwong, JC. et al. (2018). Acute myocardial infarction after laboratory-confirmed influenza infection. New England Journal of Medicine 378:345-53.

[6] Metersky M.L., Masterton R.G., Lode H., File T.M. Jr., Babinchak T. (2012). Epidemiology, microbiology, and treatment considerations for bacterial pneumonia complicating influenza. Int J Infect Dis. 2012;16:e321–331. Retrieved from: https://www.sciencedirect.com/science/article/pii/S1201971212000367?via%3Dihub 

[7]Shrestha S., Foxman B., Berus J., Van Panhuis W.G., Steiner C., Viboud C. & Rohani P. (2015). The role of influenza in the epidemiology of pneumonia. Sci Rep. 2015;5:15324. Retrieved from: https://www.ncbi.nlm.nih.gov/pubmed/26486591  

[8] Gozalo P.L., Pop-Vicas A., Feng Z., Gravenstein S., Mor V. (2012). The effect of influenza on functional decline. J Amer Geriatr Soc. 2012 Jul;60(7):1260-7. Epub 2012 Jun 21. PMID: 22724499. Retrieved from: https://www.ncbi.nlm.nih.gov/pubmed/22724499 

[9] Allard R., Leclerc P., Tremblay C., & Tannenbaum T. (2010). Diabetes and the Severity of Pandemic Influenza A (H1N1) Infection. Diabetes Care, 33(7), 1491-1493. Retrieved from: http://care.diabetesjournals.org/content/33/7/1491

[10] Bouter K. P., Diepersloot R. J., Romunde L. K., Uitslager R., Masurel N., Hoekstra J. B., & Erkelens D. W. (1991). Effect of epidemic influenza on ketoacidosis, pneumonia and death in diabetes mellitus: A hospital register survey of 1976–1979 in The Netherlands. Diabetes Research and Clinical Practice, 12(1), 61-68. Retrieved from: www.sciencedirect.com/science/article/pii/016882279190131V. Last accessed November 2019.

[11] Centers for Disease Control and Prevention (CDC). Flu and people with diabetes. Available at www.cdc.gov/flu/highrisk/diabetes.htm. Last accessed November 2019.

[12] Centers for Disease Control and Prevention (CDC). Protect against Flu: Caregivers of infants and young children. Available at www.cdc.gov/flu/highrisk/infantcare.htm. Last accessed February 2020.

[13] World Health Assembly (WHA). (2003). Prevention and control of influenza pandemics and annual pandemics. Resolution 56.19. Fifty-six WHA. Available at www.who.int/immunization/sage/1_WHA56_19_Prevention_and_control_of_influenza_pandemics.pdf. Last accessed November 2019.

[14] World Health Organization (2012). Weekly epidemiological record. Vaccines against influenza WHO position paper, 87, No. 47 p461-476. Available at www.who.int/wer/2012/wer8747.pdf. Last accessed November 2019.

[15] Centers for Disease Control and Prevention (CDC). Who needs a flu vaccine and when. Available at www.cdc.gov/flu/prevent/vaccinations.htm. Last accessed February 2020.

[16] World Health Organization. Global Influenza Strategy 2019-2030. Available at https://apps.who.int/iris/bitstream/handle/10665/311184/9789241515320-eng.pdf?sequence=9&isAllowed=y. Last accessed August 2019.

[17] World Health Organization. Influenza (Seasonal) factsheet. Available at www.who.int/en/news-room/fact-sheets/detail/influenza-(seasonal). Last accessed November 2019.

[18] Fine PEM, Mulholland K, Scott JA, et al. 77 - Community Protection. In: Orenstein WA, Offit PA, Edwards KM, eds. Plotkin's Vaccines (7th Edition): Elsevier; 2018:1512-1531.e1515

[19] Gupta, Vinay et al. (2012) Influenza Vaccination Guidelines and Vaccine Sales in Southeast Asia: 2008–2011. PLOS One 2012; 7(12). Available at www.ncbi.nlm.nih.gov/pmc/articles/PMC3528727/. Last accessed October 2019.

[20] World Health Organisation (WHO). (2019). How to implement seasonal influenza vaccination of health workers. Available at https://apps.who.int/iris/bitstream/handle/10665/325906/9789241515597-eng.pdf?ua=1. Last accessed February 2020.

[21] World Health Organisation (WHO). (2020). Guiding principles for immunization activities during the COVID-19 pandemic. Available at https://apps.who.int/iris/bitstream/handle/10665/331590/WHO-2019-nCoV-immunization_services-2020.1-eng.pdf. Last accessed May 2020

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