Influenza infects up to a billion people worldwide each year

The flu is a contagious respiratory illness caused by influenza viruses

Unlike the common cold, influenza attacks suddenly with fever, body aches, and fatigue. Seasonal strains circulate worldwide, infecting up to a billion people each year and causing hundreds of thousands of deaths despite vaccines and treatments.

A novel H1N1 influenza strain sparked a 2009 global pandemic

First detected in Mexico, the 2009 “swine flu” pandemic infected up to 1.4B people worldwide. While mortality rates were lower than earlier pandemics, the outbreak still caused more than 150,000 deaths.

Why the 1918 flu killed between 50 and 100 million people

The 1918–1920 flu pandemic (once called, incorrectly, the Spanish flu) killed quickly and in huge numbers, with estimates of the global death toll ranging from 50 to 100 million people. Several factors contributed to the high mortality rate: lack of antibiotics, the global disruption of World War I, and more.

The 1957 and 1968 influenza pandemics caused millions of deaths worldwide

The 1957 H2N2 pandemic spread from East Asia, killing more than 1M globally, while the 1968 H3N2 pandemic began in Hong Kong and caused a similar toll, with both strains rapidly moving across continents.

Flu spreads through droplets in the air and on surfaces

Influenza passes mainly through tiny droplets released when sick people cough, sneeze or talk. The virus can also survive briefly on surfaces, allowing it to spread when others touch contaminated objects.

Annual flu shots remain the best defense against influenza

Flu vaccination typically reduces the risk of medical visits by 30 to 60% and lowers hospitalization rates by around 40%. Between 2023 and 2024, in the US alone, vaccines prevented an estimated 120,000 hospitalizations and nearly 7,900 deaths.

Human records of influenza stretch back more than two millennia

Accounts of flu-like illness appear as early as 412 BCE, when Hippocrates described a sudden wave of cough and fever. Centuries of recurring outbreaks culminated in the first clearly documented pandemic in 1580, spreading from Asia into Europe and Africa.

Human records of influenza stretch back more than two millennia

Accounts of flu-like illness appear as early as 412 BCE, when Hippocrates described a sudden wave of cough and fever. Centuries of recurring outbreaks culminated in the first clearly documented pandemic in 1580, spreading from Asia into Europe and Africa.

Find out how prevalent the flu is at this current moment

Updated weekly, this USAFacts resource shares current data from the CDC detailing how many cases of influenza and other flu-like illnesses accounted for doctor's visits. Monitor the spread of respiratory illness during flu season with this handy resource and prepare accordingly.

Europe’s first recorded influenza pandemic swept the continent in 1580

The 1580 influenza pandemic, traced from Asia to Africa and into Europe, became the first flu outbreak clearly documented across the continent—killing tens of thousands and highlighting influenza’s potential for rapid global spread.

A timeline of major pandemics from 1899–2025

Modern pandemics have been defined by the race between globalization (which increases risk) and the development of new medicines. The Great Influenza epidemic claimed some 50 million lives, and the COVID-19 pandemic killed more than 7 million. In between, diseases like Ebola, cholera, AIDS, and more have devastated communities.

The measles vaccine has saved an estimated 94 million lives across the world since its introduction.

The flu vaccine has evolved alongside discoveries of new virus strains

After influenza B was identified in 1940, researchers created a two-strain vaccine by 1942. The WHO later built a global surveillance system to track mutations, enabling vaccines to be updated annually to target the strains most likely to circulate.

Fungal diseases cost the US around $19B annually.

Learn the history and science of influenza in 'This Podcast Will Kill You'

In their flu episode, cohosts Erin Welsh and Erin Allmann Updyke unpack influenza's biology, history, and impact—explaining everything from past pandemics to modern vaccines, all with their trademark mix of science and storytelling.

Major genetic shifts in flu viruses can spark global pandemics

Antigenic shift happens when two different influenza viruses infect the same host and swap genetic material. The result is a brand-new subtype of influenza which, if easily spread among people, can trigger a worldwide pandemic.

There may be 500,000 additional malaria deaths by 2050 according to peer-reviewed research published in 2026.

More than 4,000 people died from cholera in 2023

This global health threat sickened more than half a million people in 2023 and killed 4,007 people. That's a 71% increase in deaths as compared to a year earlier. (Report only offered in PDF format.)

One in 10 adults worldwide has diabetes.

West Nile was reported in 47 states in 2025, with more than 1,400 people severely affected

Tracking numbers from the CDC indicate that the virus spread widely that year, with more than 2,000 reported human cases and many states seeing more than 25 sickened people. More than 1,400 people had neuroinvasive cases of the disease—meaning the virus had entered the nervous system, which can cause severe, potentially life-threatening illness.

Small genetic changes that accumulate over time force flu vaccines to be updated regularly.

Most flu cases are treated at home, but antivirals help high-risk patients

Rest, fluids and common medicines usually ease influenza symptoms. For people at higher risk of complications, doctors may prescribe antiviral drugs, which work best when started soon after symptoms begin.

Vector-borne diseases kill more than 700,000 people globally each year—and are growing

The diseases with the greatest potential to spread widely aren't the ones that quickly kill human hosts. Instead, the best hosts or reservoirs for vector-borne diseases would be chronically ill over the long term, increasing the likelihood that the pathogen could be transmitted to others.

Antimicrobial resistance is responsible for 1.3 million deaths each year

Antimicrobial resistance is a global health threat, driven by the misuse and overuse of antimicrobials in humans, animals, and more. Estimates suggest superbugs could lead to $1T in healthcare costs by 2050, and the world faces a shortage of new drug development to meet the challenge.

Measles attacks the body's immune system, leaving it vulnerable to secondary complications.

COVID-19 vaccine breakthroughs are driving efforts toward a universal flu shot

mRNA and other technologies used for COVID-19 vaccines are being applied to influenza research. Scientists hope these advances will lead to a universal flu vaccine that protects against multiple strains and reduces the need for yearly shots.

Foodborne illnesses cost our country an estimated $74.7 billion in 2023

A US government estimate puts the cost of all foodborne illness in 2023 at almost $75 billion dollars. In a report published by the US Department of Agriculture’s Economic Research Service, government analysts detailed how the burden of foodborne illness includes medical costs, but also more hidden costs like lost wages. The analysis also breaks down estimated costs by pathogen.

Mosquitoes top the ranking of the world's deadliest animals.

Explore a 3D model of the influenza virus

This interactive 3D model reveals the influenza virus’s structure—its outer coat and spike proteins—and compares it with other well-known viruses, offering a clear view of how flu differs from pathogens like HIV or coronaviruses.

Flu viruses use special proteins to invade and spread in the body

Influenza viruses carry two key surface proteins: hemagglutinin (H), which lets them enter cells, and neuraminidase (N), which helps them escape and spread. These proteins are the basis for the names of flu subtypes like H1N1 and H3N2

Drug-resistant infections worldwide have increased by about 65% since 2000

Since 1990, antibiotic resistance has claimed at least one million lives annually and is projected to account for 39 million deaths between now and 2050 if current trends continue. The expanded use of antibiotics, particularly in agriculture, combined with a slowing pipeline of new drugs has led to the crisis.

One in six Americans contracts food poisoning each year.

Measles is one of the most contagious preventable diseases—it was eliminated in the US in 2000, but it is now making a resurgence due to declining vaccination rates.

Superbugs could claim 1.9 million lives per year by 2050

The increased use of antibiotics combined with an aging population, is projected to result in an almost 50% increase in global deaths from antimicrobial resistance each year. At the same time, antibiotic use for livestock is expected to increase by 30% over the same time frame.

Increasing contact between humans and wild animals is driving zoonotic threats

Zoonotic diseases, which spread from animals to humans, present one of the most significant emerging threats worldwide. Scientists have identified around 200 viruses capable of infecting humans, and unfortunately, the number of such diseases are on the rise—at least 60% of all emerging infectious diseases are zoonotic in origin.

Hurricanes may kill 300 times more people than officially reported

A recent study suggests that, since 1930, more than 3.5 million people have died due to hurricanes. This incorporates the long-term effects of storms on people's health and economic well-being, contributing to thousands of premature deaths each year.

Antibiotic resistance is a growing global health problem

Over decades, bacteria have grown increasingly resistant to antibiotics. This resistance now causes an estimated 1.27 million deaths each year and is associated with nearly 5 million deaths worldwide, according to the World Health Organization.

The word 'influenza' comes from a 15th-century Italian belief in the stars

In Renaissance Italy, epidemics were thought to result from the influence of natural disasters or celestial bodies. The illness was named "influenza", meaning “influence” in Italian.

Most cases of West Nile virus are asymptomatic in people

About 1 in 5 infected people develop symptoms from West Nile, including symptoms such as fatigue, head and body aches, and vomiting. But around 1% of patients develop severe complications such as encephalitis or meningitis, which can be life-threatening. Those who are most likely to become severely ill are people over age 60.

19 fungal pathogens are of key concern to world health officials

In 2022, this global health body issued its first-ever list of top fungal threats to human health. It said fungal threats are spreading and occurring more frequently. The WHO’s list included 19 fungal pathogens to watch, and said that the most dangerous ones to public health are Cryptococcus neoformans, Aspergillus fumigatus, Candida albicans, and Candida auris. There are only a handful of classes of medication currently available to combat fungal pathogens, with few others in the pipeline even though antimicrobial resistance is growing.

Hand, foot, and mouth is usually seasonal—peaking in summer—but not always

This painful, contagious disease most commonly has outbreaks in summer and early fall in the US because the enteroviruses that cause disease can most readily survive and be transmitted in warmer, humid conditions. It can still show up throughout the year, however.

See the geographic spread and incidence of malaria

This graphic shows the estimated global burden of malaria in 2025 as new cases per 1000 people at risk.

At any given time, there are an estimated 10 quintillion individual insects alive on Earth.

Rabies kills more than 50,000 worldwide each year

Rabies transmission to humans typically comes from an infected animal, and death was very common before recent protocols were developed (post-exposure prophylaxis). The virus is neurotropic, which means it has an affinity for nerve tissue, and moves quickly from broadly infecting the body to destroying the brain.

Explore a technical look at the measles virus and its toll on humanity through the ages.

Why we don't have an answer for the common cold

Since a landmark study of the common cold in 1925, researchers have learned much more about the seasonal ailment. Despite continuous study, people still contract colds for similar periods of time at the same rate with the same symptoms, and there's no vaccine. This article explains how the many viral strains make it hard to control.

Hear firsthand stories from Americans who lived through the 1918 flu pandemic

This video shares personal accounts from survivors of the 1918 influenza epidemic, capturing memories of sickness, loss, and resilience. Their voices offer a glimpse into how ordinary people experienced one of history’s deadliest pandemics.

In 2012, a virus that causes HFMD may have killed dozens of kids in Asia

More than 50 young children in Cambodia died in spring 2012 for unknown reasons, but laboratory testing of samples available from a limited number of those children came back positive for Enterovirus 71. That virus, which can cause HFMD, is known to cause severe complications among some people who contract the disease. But health officials concluded that poor baseline health and then incorrect treatment using steroids helped exacerbate their condition, helping lead to the deaths.

Bird Flu is spreading—what does that mean for us and other species?

The rapid global spread of H5N1 bird flu—from remote Antarctic islands to US farms—shows how animal spillover, driven by human activity and ecological disruption, is accelerating pandemic risk across species long before sustained human transmission begins.

HIV sidelines your immune system by destroying T cells, eventually rendering the body unable to fight off even minor illnesses.