Wastewater testing has detected genetic evidence of polio, triggering vaccine boosters

Most polio cases today are vaccine-derived rather than naturally occuring

Weakened, live virus vaccines—which aren't offered in the US—carry a risk of virus being shed in the stool. Rarely, the shed virus mutates and leads to vaccine-derived polio infections. Most recent polio cases are genetically linked to those vaccines. As shown in this graphic, there are typically hundreds of vaccine-derived polio cases annually.

Improved 19th-century sanitation meant kids encountered polio later, with worse results

Almost all children likely used to contract poliovirus, but scientists suggest that when infants encountered it very early in life—due to poorer conditions and hygiene—they still had some maternal protection from pregnancy or through breastmilk, so the symptoms were more flu-like.

Only one strain of wild poliovirus continues to infect humans

Three strains of polio used to regularly infect humans, but two of the strains were declared eradicated in 2015 and 2019, respectively. In 2019, world health leaders estimated complete polio eradication—if achieved—would save $14B by 2050.

Polio commonly spreads when virus-laden feces gets into our mouths

This highly infectious disease is transmitted from one person to another, mainly when we eat virus-laden poop particles. Less frequently, contaminated food or water can transmit the virus, or people can be infected via respiratory droplets (from coughing or sneezing).

Live virus vaccines predated polio—that's how we vaccinate against smallpox

Since 1796, smallpox vaccines have used a live poxvirus related to smallpox. Yellow fever vaccines have used a live weakened form of the virus responsible for yellow fever since 1937.

View this timeline of polio milestones and vaccine development

Polio has a long history in art and medicine, dating back centuries. It includes a representation of an apparent polio survivor with a shriveled leg in ancient Egyptian art. See milestones in the history of polio in this timeline.

The COVID-19 pandemic led to a decrease in immunizations in the US and worldwide

Public health funds and resources that were diverted to COVID-19 response reduced efforts to combat polio and vaccinations for polio and other diseases declined during the pandemic, putting more people at risk for polio.

Jonas Salk developed the first successful polio vaccine—and tested it on himself

The American medical researcher developed the inactivated virus vaccine from 1952 to 1955 and proved that it could prevent disease. He tested the virus on himself and his family in 1954 and then carried out formal clinical trials on more than 1.3 million children.

West Nile virus was detected in UK mosquitoes for the first time in 2023

Fragments of the virus were detected in mosquitoes that were being collected in Britain for the first time in 2023, but the UK government considers the overall risk to people to be low. As of spring 2026, there have never been detected locally-acquired cases of the disease.

Before vaccines, there was 'variolation': what was it?

Before the technology behind vaccinations was discovered, some keen observers of medicine around the globe noticed how previous infections could impact future ones. Learn about the techniques early physicians used before they had vaccines.

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.

Two Lyme disease vaccines were in development in 2026

As of early 2026, there was no vaccine for Lyme disease available. One candidate vaccine, VLA15, was in later-stage clinical trials. Another designed to provide seasonal protection was licensed to a pharmaceutical company in 2025, and was planned for human clinical trials.

The 2026 Ebola outbreak in the DRC is spurring new Ebola vaccine development for the Bundibugyo species.

A fake vaccine campaign was used to locate Osama bin Laden, fueling vaccine distrust

As part of the intelligence operation to find bin Laden in Pakistan, the US Central Intelligence Agency recruited a Pakistani doctor who ran a fake hepatitis B vaccine campaign and obtained DNA samples from bin Laden. News of this fake campaign fueled further distrust of healthcare workers, attacks on them, and stymied efforts to vaccinate against polio in the region.

Environmental conditions, shifting immunity, and viral strain could help explain 2025 spike

The surge in HFMD in the summer and early fall of 2025 in the mid-Atlantic could be the result of a confluence of factors, including a more virulent strain of disease-causing virus, good environmental conditions for the virus to spread—hot, humd—and a potential immunity gap among kids due to milder HFMD outbreaks the previous year.

Maryland required cholera researchers to fly a yellow warning flag—signifying quarantine dangers in the 1970s

University of Maryland Hospital researchers intentionally infected volunteers with the cholera bacterium in the late 1970s to further their understanding of the disease. They proceeded with this work following the recommendation of a US government panel. (Some users may encounter a paywall.)

A vaccine against Epstein-Barr virus, researchers hypothesize, could potentially prevent MS

As many as a quarter of MS patients have antibodies in their blood that bind to both a central protein in Epstein-Barr virus and a protein made in the brain and spinal cord that—when attacked—leads to a breakdown of protective nerve fiber insulation. This suggests the immune system's primed to attack the nervous system after mounting a defense against Epstein-Barr.

Cholera vaccines can protect people from disease for months—or even years

There are three recommended cholera vaccines on the market. The number of required shots and the period of protection they provide vary, but each of them can be life-saving.

Measles evolved from an ancient cattle disease as early as 3,000 years ago

Genetic analysis suggests that the closest modern relative of measles is a livestock virus known as rinderpest, with the viral strains diverging between 2,000 and 3,000 years ago. The timing coincided with the rise of major cities above 250,000 people, offering a novel transmission route for the newly mutated measles virus.

The 2026 Ebola outbreak is hampered by a lack of vaccine against the species of the virus, heightening the need for rapid tests to aid in disease control

Clinics in the Democratic Republic of Congo saw patients with Ebola symptoms months before the disease was identified. The identification lag was due to inadequate diagnostics that could not accurately or quickly identify the virus's myriad species. Contact tracing and better diagnostics will be required to tamp down the outbreak.

Food poisoning investigations have led to more than 1 billion pounds of food recalls

PulseNet is the US government’s real-time foodborne illness tracking system for leading causes of food poisoning. There, a network of labs and scientists share DNA sequences for pathogens collected from contaminated food and also from sickened individuals, looking for patterns in the pathogens’ genome sequences that will help them hopefully finger a certain food, warehouse, producer, or restaurant.

John Snow—not the one from 'Game of Thrones'—determined that contaminated water sickened London

His pioneering epidemiology work during an 1854 cholera outbreak mapped out the commonalities between people in London who were getting sick. He discovered that ill people were getting water from the same Broad Street pump. Before Snow's work, the prevailing theory was that bad air sickened individuals instead of cholera-causing bacteria in the water.

Leprosy has been detected in British red squirrels

The animals have been infected with both strains of the bacterium that cause leprosy. Researchers have found that squirrels living in different parts of the UK were infected with different species of the disease-causing bacteria. (Some users may experience a paywall.)

Two festival-goers were hospitalized after receiving peptide injections, raising questions

Investigative journalism shop ProPublica wrote about two people who became extremely ill following antiaging peptide injections. Authorities were examining whether the individuals were sickened by an infection, contamination related to the injections, or an issue with the medication itself, according to documents obtained by the journalists at ProPublica.

Watch how viruses like Ebola can spill over from animals to humans—and vice-versa.

Post-treatment Lyme disease syndrome may be caused by bacterial remnants in the liver

PTLDS, which refers to lingering symptoms of Lyme after antibiotic treatment, is an area of active research. Rodent research published in 2025 suggests that these ongoing symptoms may potentially be due to the body's inflammatory response to lingering cellular components from the bacteria that cause Lyme, Borrelia burgdorferi. In rodents, components of the bacteria's cellular wall may remain in the liver after the bacteria were eliminated with antibiotics.

Scientists can suck animal DNA from the air

A look at how researchers filtered the air around two zoos and identified genetic material from dozens of species, a technique that could help track and conserve wildlife.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

At the beginning of the 20th century, a group of young men ate standard American food—replete with food additives like borax and formaldehyde—as part of government research to better understand food safety.

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

Fireworks-related ER visits are on the rise—in 2024, they increased by 52% as compared to the prior year.

Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

In 1915, workers recovered a submarine-like vessel from the Chicago River, prompting fears of German espionage

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

Elk Cloner, the first computer virus to spread in public, was written as a practical joke by Richard Skrenta, a Pittsburgh high school student.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

NBA superstar Victor Wembanyama spent the 2025 summer training with monks in central China to enhance his body and mind.

Electrical grids worldwide must double their power delivery capacity by 2050 to meet surging demand from AI and electric vehicles.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

After 25 people used virtual reality headsets to practice flying with virtual wings—flapping their arms—their visual cortex responded to the wings almost as if they were real arms, treating them as body parts.

In 2025, four executives from large tech companies were given positions in the US Army Reserves—including Palantir Chief Technology Officer Shyam Sankar, which reinforced Palantir's ties with the US military and its role as a leading defense partner.

Children are now three times more likely to say they want to be a YouTuber when they grow up than an astronaut, with some even attending 'YouTube camps' that teach kids how to create content for the platform.

For centuries, Niagara Falls has been a magnet for daredevils seeking to conquer one of nature's most powerful wonders, with its 200-foot drop and water rushing at 32 feet per second with 280 tons of force.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

A pickleball's loud 'pop' sound can reach 120 decibels, which is equivalent to a hammer hitting a nail