Flu vaccines are reformulated each year based on global predictions

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.

Small genetic changes force flu vaccines to be updated regularly

Through a process called antigenic drift, influenza viruses accumulate tiny copying mistakes in their genes. These gradual changes alter the virus enough that immunity fades, making updated vaccines necessary each flu season.

Most flu vaccines are still produced using chicken eggs

For decades, influenza vaccines have been made by growing viruses inside fertilized chicken eggs. Though newer methods using cell cultures or recombinant technology exist, egg-based production remains the primary global manufacturing process.

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.

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.

The best time to get a flu vaccine may be late-September or early-October

The body needs a few weeks after the vaccine to build up a sufficient antibody response, which eventually wanes. Scheduling the vaccine accordingly can maximize its effectiveness when flu season ramps up.

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.

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.

Certain vaccinations may be more effective when given around the middle of the day

A 2023 analysis of the health records of more than 1.5 million people in Israel suggests that COVID-19 vaccines may be more effective when received around the middle of the day. Separate early research also suggests there may be similar trends for influenza vaccines.

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.

Malaria vaccines are not routine because they have limited effectiveness

Both of the currently recommended malaria vaccines have limited effectiveness, require multiple doses, and provide protection for only a short period of time. One, approved by the World Health Organization in 2021, is only about 30% effective, requires four doses, and protection fades within months. The other requires three shots, and some research indicates it is 75% effective for a year.

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.

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.

An Ebola vaccine was developed during the 2018 west African Ebola outbreak, but the 2026 Ebola outbreak is with a different species of the virus, not the one that the vaccine is approved to treat.

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.

The business models behind vaccines

Watch experts weigh in on the prevailing business models of vaccine production, including how the Covid-19 pandemic has disrupted the industry for good in this 20-minute video from Financial Times.

See the evolution of Ebola vaccine and treatment development

The recently approved vaccine and treatments against Ebola are the result of many years of investments and have reshaped how the world addresses Ebola outbreaks. Four drugs were tested in the midst of the 2014 outbreak. Two proved to be so effective the clinical trial ended early. The vaccine proved effective during the 2018-2020 outbreak in the DRC.

The oral, live virus vaccine is the most robust but carries more risks

The live virus vaccine, delivered via oral drops, induces the best protection in the body. Because it includes a live, weakened form of the virus there's an extremely small risk it can sicken recipients and potentially cause paralysis. Recipients also shed the virus in their stool, which can rarely lead to vaccine-derived cases of the virus if the virus mutates. (Some users may experience a paywall.)

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.

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.

A history of vaccine rollouts

History tells us the public will tolerate risk of harm from a vaccine if their fear of the disease exceeds their fear of the vaccine.

Experimental hantavirus vaccines and therapies, still under development, have long been funded by the US military.

California condors have been vaccinated against West Nile to protect their limited population

The condors became endangered in the 20th century primarily due to lead poisoning from consuming animals shot with lead bullet fragments inside them, so condors in captivity and in the wild are vaccinated against diseases including highly pathogenic avian flu and West Nile.

See the differences between the Wegovy pill and injection

Examine this chart that compares and contrasts the oral and injectable Wegovy formulations. The differences include how they are absorbed by the body (through the digestive tract versus subcutaneously), their dosages, and the required timing (the pill is taken daily and has specialized timing requirements, while the injected form is administered once a week). Importantly, the pill form is also approved to treat fewer conditions.

Fluorinated molecules are the most impactful, longest-lasting greenhouse gases

Developed as replacements for ozone-depleting substances in refrigeration and air conditioning systems, these compounds are released through leaks in and ongoing use of these appliances, as well as from various industrial processes. They can remain in the atmosphere for thousands of years and have warming potentials that are a thousand to tens of thousands of times greater than those of carbon dioxide.

Eruption forecasting relies on probabilistic methods resembling weather forecasting

While some volcanoes erupt with predictable signs, such as surface deformation from the build-up of underground magma pressure, others release magma at inconsistent rates. Extensive monitoring is needed to identify less clear patterns and indicators of future eruptions.

Hormone and peptide compounds imported from China soared in 2025

US customs data indicates that these imports doubled to $328M in the first three quarters of 2025, from $164M in the same period of 2024. The imports include GLPs, among other products. (Some users may experience a paywall.)

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

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

This real-time tracking of the hantavirus cruise ship outbreak in May 2026 offers a unique glimpse into the global reach of the outbreak and whether the virus sickened passengers and their communities around the world.

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

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.

Telehealth demand for GLP-1s for weight loss is booming as consumers seek easier access.

Scientists testing how climate change affects plants found, in a years-long simulation study, that poison ivy grew 70% faster with the resulting extra carbon dioxide.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

Doctors differentiate between a phobia and fear by asking patients whether their fear interferes with their day-to-day activities.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

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

Calculate how much of your tax dollars go to each federal program based on your income, filing status, and number of children

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.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

Tattoos remain visible on your skin thanks to immune cells called macrophages

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

Hotels in Cannes, the glamorous city on the French Riviera, hire hawks to ward off seagulls during the city's famous film festival.

In preparation for this weekend's Eurovision finale, which is something like the World Cup of pop music, here's a young Céline Dion performing (for Switzerland?) at the 1988 competition.

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