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

See the polio cases that occur worldwide each year by region

Worldwide, the number of cases of polio reported each year from 1980 to 2024 has declined. This graphic depicts regional trends and declines by year.

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.

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.

Oral polio vaccines cause approximately 250 to 500 polio cases per year globally

Live, weakened polioviruses in the oral vaccine can very rarely mutate into a disease-causing form and lead to vaccine-associated paralytic poliomyelitis. This oral vaccine is not available in the United States.

Polio is currently circulating in only two countries but it remains difficult to eradicate

Wild polio virus is only endemic in two places. Afghanistan and Pakistan are the last two countries with naturally occurring polio cases. Vaccination campaigns have been plagued by misinformation, Taliban bans on vaccines, distrust of public health workers, and violence, including the killing of vaccinators.

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.

See when the last case of wild poliovirus was found in each country

This chart shows when wild polio cases were last reported in each country worldwide. Beyond wild poliovirus, rare outbreaks can occur related to mutated strains of oral polio vaccine.

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

Sampling of wastewater in London in 2022 detected fragments of polio virus, suggesting a vaccine-derived version of polio may be circulating. No one became ill, but the finding did trigger calls for a renewed booster inoculation campaign.

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).

Inactivated polio virus vaccine is the only one offered in the US—it contains no live virus

Inactivated polio virus vaccines cannot cause illness because the virus isn't alive. It's been the only polio inoculation offered in the United States since 2000 and provides almost complete protection

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.

COVID accelerated antibiotic resistance

The COVID-19 pandemic was caused by a virus, and viruses can’t be treated with antibiotics. But recent research finds that COVID patients were given a tremendous amount of antibiotics, contributing to the problem of antibiotic-resistant bacteria. Why? This NPR feature sheds light on an unexpected side effect of the pandemic.

Needle-free polio vaccines were offered in Afghanistan for the first time in 2026

Fear of needles has been one barrier to eradicating polio in Afghanistan. Vaccinators are now using a needle-free jet injector to deliver the vaccine through the skin—an approach that's previously been used in other locations. The inoculation includes the inactivated virus vaccine (the vaccine without any live virus in it).

How the 1918 pandemic spurred developments in virology and vaccines

This article provides an in-depth historical account of the 1918 Spanish Flu pandemic, including its impact on the global population and how its occurrence spurred significant advancements in the study of viruses—laying the groundwork for the...

How the World Bank's pandemic bonds were triggered during COVID-19

In 2017, the World Bank raised a chunk of emergency funds through bonds to help developing countries cover funds in the event of a pandemic. Had no pandemic occurred, investors would have received returns of 6% to 11%. But the global pandemic meant they lost all their money.

A heatmap showing the drop in infectious diseases post-vaccine deployment

The number of infected people, measured over 70-some years and across all 50 states and the District of Columbia, declined significantly after vaccines were introduced.

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.

A major US-designed polio vaccine was first tested in the Soviet Union

Albert Sabin's live attenuated virus vaccine—requiring two drops in the mouth—didn't garner political support in the US, so it was tested in the Soviet Union in the late 1950s.

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.

How did the pandemic affect mental health?

Read this research brief to learn more about why heightened mental health and substance use concerns persist three years after the outbreak of COVID-19. According to a recent survey, the vast majority of American adults view the nation as facing a...

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.

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.

Policies related to the coronavirus pandemic inadvertently increased illegal border crossings

A pandemic-era public health measure called Title 42—intended to seal the border by expelling migrants immediately—backfired. Because expulsions carried no legal consequences, migrants simply tried again, driving illegal crossings to a peak of over 370,000 people in December 2023.

Approximately 70% of all polio infections in children are asymptomatic

Most polio infections are asymptomatic or appear with only flu-like symptoms. Infected individuals can still shed the virus in their stool and mucus for days or weeks

Diphtheria was once a leading childhood killer before antibiotics and vaccines

In 18th- and 19th-century outbreaks, some New England families lost as many as eight children to diphtheria, and fatality rates in hospitals often topped 60%. The invention of antitoxins, penicillin, and vaccines dramatically reduced deaths.

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

Paralysis from polio occurs in under 1% of infections

About 1 in 200 cases of infection causes paralysis. For paralysis to occur, the virus travels from the throat, intestines, and gut to infect specific cells within the spinal cord and brain stem that control movements. Within hours of invading the nervous system, paralysis can occur. The virus can be present in bodily secretions and stool for multiple weeks post-infection.

Our World in Data's COVID-19 tracker, with global case, death, and vaccination data for every country, though updates to the dataset ended in 2024.

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.

Severe cases of food poisoning have doubled even as food recalls dropped

Food recalls were down in 2024 by 5% as compared to 2023. But some researchers suspect that’s just because there were fewer inspections or fewer people reporting illnesses: Hospitalizations from food poisoning more than doubled during that same period, from 230 to 487, and deaths rose from 8 to 19.

Humans are the only known reservoir of poliovirus

The virus has not been found in any other species, which makes humans the only known reservoir for polio. In laboratory settings, nonhuman primates have also been infected with the virus, but there's no evidence that they contract the virus in nature.

The federal government pumped $70 billion into transit amidst reduced ridership during the COVID pandemic

When ridership collapsed by 75% in the spring of 2020, Congress sent transit agencies nearly $70B to help them survive. But that money has largely run out, and ridership remains 14-28% below prepandemic levels, leaving many transit systems with large budget deficits.

Visualizing the genetics of SARS-CoV-2

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, began with an outbreak in Wuhan, China in December 2019, and rapidly spread worldwide in early 2020. On March 11, 2020, the World Health Organization declared COVID-19 a global pandemic, leading to widespread lockdowns, travel restrictions, and economic disruptions.

Measles cases in the US reached a 35-year high in 2026 as vaccination rates dropped.

The US developed a coin circulation problem in 2020

As people reduced the frequency with which they paid for things in cash and change during the COVID-19 pandemic, opting for tap-to-pay systems or online shopping instead, the number of coins in circulation decreased. Those who did make cash purchases were more likely to keep their change at home rather than use it on a subsequent purchase.

Variola: the second-deadliest virus on Earth

Because it was declared eradicated in 1980, many forget smallpox is one of history's deadliest diseases—in its final century, it's estimated to have claimed 500 million lives. This 11-minute video from production studio Kurzgesagt takes a look at...

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.

Post-polio syndrome occurs decades after infection but isn't contagious

Affecting adults who contracted polio as children, this disorder can occur 15 to 40 years later, leading to slow, irreversible muscle weakening. Some research estimates that between 25% and 40% of polio survivors go on to develop this condition.

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.

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.)

Measles was declared eliminated in the US in 2000, meaning the country had been free of continuous disease transmission for 12 months or more.

The pandemic forged new FIRE followers

The FIRE movement gained steam during the pandemic, when some were inspired to clean financial house amid an environment of global economic uncertainty.

COVID-19's shock to employment rates sparked some economists to fear deflation

COVID-19 simultaneously disrupted the supply chain and the labor market. Since the unemployment rate had hit record highs, some economists were worried that the supply chain would recover before the labor market. If that had happened, businesses would have been producing goods, but no one would have been able to buy them because they wouldn't have the disposable income to do so.

Read about Palantir's role in the COVID-19 vaccine rollout

Palantir developed Tiberius, a software service that supported the public-private partnership spearheaded by then-President Trump to roll out COVID-19 vaccines. The software tracked state-by-state vaccine allocations, as well as COVID-related hospitalizations.

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.

During the COVID-19 pandemic, many private schools offered in-person classes

By early 2021, approximately 76% of private schools offered some form of in-person learning compared with 38% of public schools.

During COVID-19, the Fed made drastic moves in attempts to shore up the US economy called quantitative easing

The Fed took an aggressive approach to help the US economy during COVID-19 beyond standard monetary levers, including broad purchases of mortgage-backed securities, Treasury securities, and more.

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.

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.

Explore US public health data

This resource tracks key US health metrics, including mortality causes, child survival rates, and life expectancy comparisons, to inform future health improvements, with regularly updated global estimates.