Pandemic Influenza (Human)

Primary reference(s)

WHO, 2019. Global influenza strategy 2019-2030. Geneva: World Health Organization; 2019. Licence: CC BY-NC-SA 3.0 IGO. World Health Organization (WHO). Accessed 27 May 2025.

Annotations

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Drivers

A pandemic occurs when an influenza virus emerges to which there is little or no immunity in the global human population and which can transmit efficiently among people. The pandemic virus can be a virus strain jumping directly from animals or reassorted from animal viruses with or without human seasonal viruses (WHO, no date a; WHO EURO, no date). 

Impacts

Influenza pandemics, whether mild, moderate or severe, affect a large proportion of the global population, which puts significant strains on health and other essential services and may result in significant economic losses (WHO, no date a). 

WHO recommends annual vaccination for high-risk groups including health care workers. People should ideally get vaccinated just before the influenza season begins for the most effective coverage, although getting vaccinated at any time during the influenza season can still help prevent flu infections. The best way to avoid getting the flu is to get the flu vaccine every year. Influenza viruses evolve constantly, and twice a year WHO makes recommendations to update the vaccine compositions. For the 2016-2017 northern hemisphere influenza season, the vaccine formulation was updated in February 2016 to contain two type A viruses (H1N1 and H3N2), and a type B virus (WHO, 2020). 

In 2018, the world observed the centenary of the start of the 1918–1919 influenza pandemic. Its estimated toll of up to 50 million deaths exceeded that of the First World War, resulting in a dramatic decline in life expectancy in many countries at the time of the pandemic. Its impact led to fundamental changes in public health and health-care systems, including centralized and consolidated health-care, greater recognition of the role of socioeconomics in health, and the coordination of public health at national and global levels.  

Since the 1918–1919 pandemic, there has been significant progress in medical science, including the development of influenza vaccines, antiviral drugs and better diagnostics. Subsequent pandemics occurred in 1957–1958, 1968–1969 and 2009–2010, resulting in 1–4 million, 1–4 million and 100,000–400,000 deaths, respectively.  

The pandemic (H1N1) 2009 caused significant deaths, particularly in those aged under 65 years; it also tested national health response systems, in particular, the pandemic vaccine response capacity) and exposed weaknesses in those systems. It reiterated that influenza viruses of both avian and swine origin can cause a pandemic, and it underscored the importance of intersectoral collaboration for pandemic preparedness.  

Although it is impossible to predict when the next pandemic might occur, its occurrence is considered inevitable, and it could well occur during the time frame of this strategy. Given increased economic globalization, urbanization and mobility, the next pandemic will spread further and faster and could lead to significant disruptions. Despite significant medical advances over the past 100 years, there will still be populations that have limited access to care and will be likely to experience high mortality rates during a pandemic.

Multi-hazard context

Not Applicable.

Risk Management

Timely detection, characterisation and sharing of information about the pandemic virus directly affects the outcome of all downstream responses. The WHO GISRS is the foundation of such an operation. In an influenza pandemic, the virus is likely to spread rapidly. Rapid development, production and deployment of vaccines are critical to limit the potential impact on populations and essential services. Access to the appropriate vaccine in the early phases of a pandemic is greatly influenced by global production capacity and the lead time required to produce influenza vaccines (WHO, no date a). 

As an influenza pandemic may last months or even years, it may require a sustained response in the health sector but also in other sectors providing essential services, such as energy and food production (WHO, no date a; WHO; 2025 b). 

The Pandemic Influenza Preparedness Framework, or PIP Framework, is an innovative access and benefit-sharing instrument that seeks to better prepare the world to respond more equitably to the next influenza pandemic. The PIP Framework was adopted on 24 May 2011 by the 194 Member States of WHO, recognizing that an influenza pandemic would be a global challenge, and preparing for it requires a holistic, collective and cooperative approach. WHO implements the PIP Framework in close partnership with Member States and public health laboratories that are specialized in influenza, industry and civil society. The PIP Framework enables the sharing by WHO Member States of influenza viruses with human pandemic potential with the Global Influenza Surveillance and Response System (GISRS) and equitable access to vaccines, medicines and other products and technologies. Under the Framework, Member States are expected to share their influenza viruses with pandemic potential (IVPPs) in a rapid, systematic and timely manner with GISRS, a WHO-coordinated global network of public health laboratories. In addition to serving as a virus-sharing platform, GISRS also develops – inter alia – candidate vaccine viruses, and other analyses, materials and information that are shared with Member States and manufacturers of influenza vaccines and other products, such as antivirals and diagnostics (WHO, 2024a). 

Globally coordinated surveillance of influenza, timely sharing of influenza virus data and associated information, and innovative research are key to addressing the problem of influenza. Global influenza surveillance has been conducted through the World Health Organization (WHO) Global Influenza Surveillance and Response System (GISRS) since 1952. GISRS is a system fostering global confidence for over half a century, through effective collaboration and sharing of viruses, data and benefits based on Member States’ commitment to a global public health model (WHO, 2024b). 

The aim of GISRS is to protect people from the threat of influenza by functioning: as a global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza; as a global platform for monitoring influenza epidemiology and disease; and as a global alert for novel influenza viruses and other respiratory pathogens (WHO, 2024b). 

One Health measures to mitigate the risk of pandemic influenza adapting to mammals and humans focus on limiting exposure and preventing spread. Key options for actions include enhancing surveillance targeting humans and animals, ensuring access to rapid diagnostics, promoting collaboration between animal and human sectors, and considering the implementation of preventive measures such as vaccination of poultry. Effective communication with different target audiences should be emphasised, as well as strengthening veterinary infrastructure, enforcing biosecurity measures at farms, and reducing wildlife contact with domestic animals (EFSA & ECDC, 2024).

Monitoring

Global influenza surveillance has been conducted through WHO's Global Influenza Surveillance and Response System (GISRS) since 1952 (WHO, 2924b). GISRS is a system fostering global confidence and trust for over half a century, through effective collaboration and sharing of viruses, data and benefits based on Member States' commitment to a global public health model.

The mission of GISRS is to protect people from the threat of influenza by continuously functioning as a:

• global mechanism of surveillance, preparedness and response for seasonal, pandemic and zoonotic influenza;
• global platform for monitoring influenza epidemiology and disease; and
• global alert for novel influenza viruses and other respiratory pathogens.

The table below offers an overview of monitoring for pandemic influenza. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, no date b).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, no date, b).