The start of a new year often brings renewed motivation to make healthier choices. But as 2026 begins, optimism about America’s health is tempered by troubling trends—most notably, declining childhood vaccination rates and a rise in school immunization exemptions. Together, these shifts are creating new opportunities for infectious diseases to spread.
These patterns predate Robert F. Kennedy Jr.’s tenure as secretary of Health and Human Services, yet public health experts fear the situation could deteriorate further. Kennedy has repeatedly questioned the safety and effectiveness of vaccines and has overseen changes that significantly reduce the number of shots recommended for children—moves that have drawn sharp criticism from the medical community.
“I think it’s going to get worse before it gets better,” says Michael Moody, a pediatrics professor at Duke University School of Medicine.
When communities contain large numbers of unvaccinated or under-vaccinated individuals, infectious diseases can spread rapidly—especially illnesses many Americans have never encountered because vaccines once kept them rare.
“People tend to romanticize diseases they haven’t seen,” Moody says. “You forget how serious they really are.”
Vaccines and high immunization coverage have long shielded the U.S. from widespread outbreaks. But if vaccination rates continue to fall, experts warn the consequences could be severe.
“We’re victims of our own success,” Moody says. “I worry we’ll need to see really bad outcomes before people remember why these vaccines exist.”
Against that backdrop, here are five infectious diseases to monitor closely in 2026.
Flu
Flu season is already in full swing, driven in part by a newly circulating variant. The Centers for Disease Control and Prevention estimates that this season has already caused at least 15 million illnesses, 180,000 hospitalizations, and 7,400 deaths—including 17 among children.
“Last year was a significant flu year,” Moody says. “We hoped this one might be quieter, but it’s shaping up to be very similar.”
Less than half of U.S. children have received a flu shot this season, according to CDC data—lower than at the same point in any of the past six years.
Until recently, annual flu vaccination was recommended for everyone aged 6 months and older. That guidance has now changed. Flu vaccines—along with shots for RSV, meningococcal disease, and COVID-19—are now recommended only for children considered high-risk or following shared decision-making between parents and clinicians.
Medical organizations strongly opposed the change.
“At a time when families need clear, evidence-based guidance, this decision will only increase confusion and undermine confidence in vaccines,” said Andrew Racine, president of the American Academy of Pediatrics.
Last flu season was the deadliest for U.S. children in more than a decade, with 280 pediatric deaths.
Measles
The U.S. reported more than 2,000 measles cases in 2025—the highest annual total in decades and the largest surge since the disease was declared eliminated in 2000.
Active outbreaks continue to grow in South Carolina, while others that emerged in Utah and Arizona last summer remain ongoing.
If these trends persist, the U.S. risks losing its measles elimination status—a symbolic and practical setback that reflects declining trust in vaccines and heightened danger for children and vulnerable populations.
“This vaccine has been studied for decades,” says Derek Cummings, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health. “It’s one of the greatest public health tools ever created and has saved millions of lives.”
Polio
Polio—a highly contagious virus that can cause paralysis or death—remains a major concern for public health experts.
The disease was eliminated in the U.S. thanks to widespread vaccination, but declining immunization rates have reopened the door to its return. Kennedy has publicly questioned polio vaccines, at times making misleading claims about their safety.
While polio no longer circulates in the U.S., it remains endemic in Pakistan and Afghanistan. As long as the virus exists anywhere, unvaccinated American communities remain at risk.
“That’s the one I worry about most,” Moody says. “It’s still out there, and it spreads easily.”
Disease X
Disease X is not a specific virus but a placeholder name for an unknown pathogen that could cause the next major outbreak or pandemic.
The concept exists to ensure governments and scientists actively prepare for future threats—rather than reacting after a crisis begins.
“We’re preparing for the future,” said Ana Maria Henao Restrepo of the World Health Organization in a 2024 podcast. “Disease X represents the unknown virus or bacteria that could spark the next epidemic or pandemic.”
However, recent cuts to public health data collection and reductions in funding for mRNA vaccine research have raised concerns that the U.S. may be less prepared than it should be. Experts stress that another pandemic is inevitable—the only question is when.
Bird Flu
The CDC currently considers the public health risk from bird flu to be low but says it is closely monitoring the situation.
Human-to-human transmission has not been documented in the U.S. Yet the virus is widespread among wild birds and has caused outbreaks in poultry and dairy cows. Since 2024, more than 70 human cases and two deaths have been reported, primarily among dairy and poultry workers.
“What’s concerning is that the virus isn’t limited to birds anymore,” Cummings says. “Its ability to infect multiple species is a warning sign of a pathogen with real pandemic potential.”
