The FIFA World Cup has officially kicked off, uniting soccer fans around the world. The massive sporting event is expected to spread fun and connection, but also germs, according to experts. The 16 cities hosting games — including 11 in the United States — are anticipating teams from 48 count ries and millions of fans. It’s the biggest and longest tournament in FIFA history. According to infectious disease doctors, this makes the event ripe for the transmission of pathogens. “What’s different about the World Cup is this is not a one-day thing. It’s spanning over six weeks and bringing in millions of additional visitors to U.S. cities,” Syra Madad, an infectious disease epidemiologist at Harvard University’s Belfer Center, tells TODAY.com. Games will take place across the U.S., Canada and Mexico. Fans will pour into stadiums, fan zones and watch parties. “Mass gathering dynamics always increase the risk for infectious disease because you have congregate settings with high concentrations of people … within the stadiums, airports, hotels and bars,” Dr. Tyler Evans, an infectious disease physician and CEO of the Wellness Equity Alliance, tells TODAY.com. Several factors make this World Cup “uniquely risky,” he says. First, there are potential immunity gaps among international visitors and the U.S. population. “We’re not tracking people’s (health) records, so there’s going to be variable degrees of immunity from vaccinations,” says Evans. Attendees will share bathrooms and eating spaces. “There’s also major (hand) hygiene gaps,” Evans adds. A surge in sick people could fill up local emergency rooms and urgent care centers, creating bottlenecks. These risk factors could allow pathogens to cross a “tipping point,” leading to an outbreak, Evans says. “We don’t want to alarm people. We want to inform people so that they can make the right decisions, think through the risks and benefits, (and) know how to protect themselves,” adds Evans, who plans to attend several games. World Cup 14 hours ago Empty seats on World Cup's opening day renew ticket price concerns 2026 World Cup Jun 11 Mexico tops South Africa 2-0 in World Cup opener with three red cards 2026 World Cup Jun 10 One potential breakout star for every nation at the 2026 FIFA World Cup World Cup 2026 Infectious Disease Risks “There’s a full spectrum of (health hazards) we can anticipate,” says Madad. Infectious diseases remain a top concern due to the nature of the event. Health officials are already preparing for potential crises. “We don’t need to panic. It’s all about preparedness to prevent that panic … having policies, protocols and plans,” Madad says. Scientists are monitoring wastewater data for warning signs. Last week, Georgetown University and MedStar Health in Washington, D.C., launched the Health Security Operations Center to track potential disease outbreaks related to the World Cup. “We’re bringing together diverse sources of disease surveillance information across jurisdictions and then sharing it back with public health and healthcare authorities,” Rebecca Katz, Ph.D., a professor at the Georgetown School of Medicine and head of the Health Security Operations Center, tells TODAY.com. Here are the infectious diseases that could spread during the World Cup, listed from highest to lowest level of risk. Measles The pathogen of top concern isn’t Ebola or hantavirus — it’s measles, says Katz. Measles is the most contagious disease in the world. The reproduction number (R0) — the average number of new cases caused by one infected person — is 12–18, says Evans. That means one person with measles can infect up to 18 people who aren’t fully vaccinated. (For context, the R0 for COVID-19 and influenza is one to three, says Evans.) The measles virus is airborne and spreads easily in crowded settings. For every “GOAL!” cheered, imagine how many respiratory droplets are spewed into the air. The contagiousness of measles, combined with immunity gaps and a congregate setting could create an explosion in cases. Measles has already made a comeback in the U.S. due to falling vaccination rates. There have been at least 2,000 cases in the U.S. this year alone, per the Centers for Disease Control and Prevention. It’s also surging around the world. “One of the ways we get measles (outbreaks) in this country is through importation, and when we have pockets of low vaccination rates, that’s where it starts to spread,” says Madad. Experts agree that a measles outbreak during the World Cup would “not be surprising.” Respiratory viruses You can also expect colds, COVID-19 and flu to show up to the World Cup. Although it’s summer, these respiratory viruses can spread year-round. “We’re at low levels of flu and COVID right now, but it doesn’t mean they’re gone,” says Madad. Plus, some attendees are visiting from countries during their winter, aka flu season. These viruses transmit primarily through inhaling respiratory droplets and spread efficiently in crowded settings. Although many stadiums are outdoors, this doesn’t eliminate the risk. “When you’re in a crowd for a long period of time, sharing the same airspace, there’s always a threat of spreading respiratory viruses,” Madad adds. Uptake of the COVID-19 and flu shots has also decreased, Evans notes, which leaves a larger portion of people vulnerable. “These may not seem as concerning as other (diseases), but they could definitely spike up,” Evans adds. Gastrointestinal illness Norovirus, salmonella, E. coli and other gastrointestinal bugs spread easily in settings like the World Cup. People contract these from consuming contaminated food and water, or touching contaminated surfaces via the “fecal-oral route.” Tiny particles from feces can wind up in food, on doorknobs or unwashed hands, then enter the mouth. “Poop is everywhere, a lot of people do not wash their hands,” says Evans. Norovirus is particularly infectious, and it only takes a few particles to make you sick. “Outbreaks are common during these mass gatherings,” says Madad. Food-borne illness outbreaks can spawn from just one ingredient or kitchen contaminated with bacteria. “People are all eating from the same food vendors,” Evans adds. These illnesses are usually mild but can be severe in people who have weaker immune systems. Mosquito-borne diseases Diseases like dengue, Zika and chikungunya are another concern, says Madad. These arboviruses are spread by certain species of mosquitoes found in the U.S. and Mexico. The World Cup will take place during peak mosquito season in some cities, like Houston and Miami, which increases the risk of transmission. There’s also a risk of cases being imported by visitors from endemic regions, then spreading locally. Most cases of dengue in the U.S. are from travelers infected elsewhere, per the CDC. “We expect we might see a few cases of dengue, but not large outbreaks,” says Katz. Sexually transmitted infections The World Cup — and the fun it will bring — may increase the risk of sexually transmitted infections. “You’ve got this big event, and there’s parties and drinking and with that comes sex, so STIs may spike up,” says Evans. Top players include chlamydia and gonorrhea. “We’re carefully watching mpox,” says Katz. “We always see reductions of condom use around the summertime,” Evans adds. Ebola and hantavirus are low risk Although the world has been fixated on recent outbreaks of Andes hantavirus and Ebola, experts aren’t as concerned about these compared to more familiar infectious diseases. Ebola and hantavirus are considered “high consequence but low probability” events, says Madad. In other words, these rare pathogens cause serious and often fatal disease, but they’re unlikely to cause large outbreaks linked to the World Cup. That’s because they don’t spread as easily from person to person or through casual contact. Experts remain concerned about the Ebola outbreak in the Democratic Republic of Congo, which has killed 140 so far, but emphasize that the risk Ebola spreading in the U.S. is very low. Other health risks Other risks during the World Cup include heat-related illness and accidents, says Madad. Many games will take place during hot temperatures, which increases the risk of exhaustion and heat stroke. “You also have to consider injuries from being in a mass crowd,” says Madad. These include falls, fights or deadly “crowd crushes.” There’s also a risk of cardiac events, which are more likely to occur while viewing a stressful soccer match, research shows. How to protect yourself First, stay up to date with immunizations. “The biggest thing is to decrease the risk of being susceptible to infectious diseases. The best tool to do that is vaccines,” says Madad. Whether it’s measles or COVID, make sure you’re fully vaccinated. Hand hygiene is crucial. Always clean your hands after using the bathroom and before eating or touching your face. “Washing your hands with soap and water is the gold standard, but use alcohol-based hand sanitizer if you can’t,” says Madad. If you’re sick, stay home or wear a mask while attending events. “I don’t think everybody needs to be wearing a mask at the World Cup, but if you are (high risk) or people in your household are, I’d recommend wearing one,” says Evans. High-risk groups include adults over the age of 65 and immunocompromised people. Even if you’re healthy, it’s a good idea to carry a well-fitting mask in case, Madad says. It’s also important to stay hydrated and wear sunblock, the experts note. While partying, be mindful of your alcohol consumption, and if you decide to have sex, use condoms. “There’s no magic bullet. It’s about doing all these things together to make sure people gather as safely as possible,” says Madad. While there are risks, there are also benefits to this event — socializing, fun, community. “It’s so exciting. The World Cup is an opportunity to peacefully compete with other countries, and there’s a healthy catharsis to that,” says Evans. This story first appeared on TODAY.com. 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