Johns Hopkins Experts Warn of Mounting Threats
The United States reported 1,912 confirmed measles cases through December 9, 2025—the highest number since 2000 when measles was declared eliminated—as public health experts warned of converging threats from vaccine-preventable diseases and seasonal respiratory viruses during a December 16 media briefing at Johns Hopkins Bloomberg School of Public Health.
The measles resurgence, driven primarily by a 129-case outbreak in South Carolina, resulted in three deaths in 2025, with 92% of cases occurring in unvaccinated patients or those with unknown vaccination status, according to William Moss, MD, Professor in the Departments of Epidemiology, International Health, and Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health as well as Executive Director of the Bloomberg School of Public Health's International Vaccine Access Center (IVAC). The experts indicated that public health costs averaged $43,000 per case, with a range from $7,000 to nearly $250,000 depending on outbreak size.
"We've certainly been tracking measles very carefully this year, after having historic low numbers here in the United States and globally during the early years of the pandemic," Dr. Moss said during the briefing. The age distribution of cases was unexpected, with approximately 25% occurring in pediatric patients younger than 5 years and about 33% in adult patients older than 20 years. "[T]his reflects the fact that we've had this long-standing undervaccination in some communities here in the United States where these outbreaks are occurring," he added.
Dr. Moss advised against routine antibody testing to verify measles immunity, noting the Centers for Disease Control and Prevention (CDC) doesn't recommend this practice except for specific groups such as pregnant women and health care providers. Among those uncertain of vaccination status, revaccination is recommended rather than testing.
Elimination Status in Jeopardy
The United States risks losing its measles elimination status if continuous transmission can be demonstrated from January 2025 through January 2026. Dr. Moss explained that elimination is defined as the absence of continuous transmission of measles virus in a defined geographic area for 12 months or more.
"[I]f we can demonstrate that measles virus transmission has kind of continued throughout this year into January of 2026, the United States is also at risk of losing its measles elimination status," Dr. Moss said. The Americas lost its elimination status in November 2025 when Canada reported losing its status.
Determining continuous transmission has proven complex. While all US outbreaks involve the D8 genotype, standard genotyping based on a small viral region lacks sufficient resolution. "[S]tates are working with the CDC, are doing more what we call whole genome sequencing, basically sequencing the whole measles virus genome, and that's going to allow us, give us much finer resolution, on, the relationship between the strains," explained Dr. Moss.
Preliminary genomic analysis from Jim O'Neill, Acting Director of the CDC, suggested Utah and Arizona cases weren't directly linked to the West Texas outbreak; however, formal data haven't been released. The Pan American Health Organization and World Health Organization (WHO) will work with the CDC in January to make a final determination, with Dr. Moss noting "the burden of proof is going to be on those who claim that it was not [continuous transmission]."
H3N2 Subclade K Drives Influenza Season
Simultaneously, a new H3N2 influenza variant designated clade K emerged as the dominant circulating strain in the United States, having already driven earlier influenza seasons in Australia, the United Kingdom, Japan, and Canada. Andy Pekosz, PhD, Professor and Vice Chair of the W. Harry Feinstone Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health, described how the variant contains mutations affecting two key antibody-binding sites on the viral protein.
"It has mutations that may allow it to evade some, but not all, of the influenze vaccine-induced protection," Dr. Pekosz said. "The clade K virus seems to be driving influenza cases in England, Canada, and Japan. [T]he CDC is reporting that it's the dominant influenza virus strain that's circulating here in the US population."
States like Colorado, Louisiana, and New York are experiencing rapid increases in influenza cases. While clade K is associated with increased case numbers, the experts are still determining whether it produces inherently more severe illness or if hospitalizations are rising proportionally with the overall case surge.
However, Dr. Pekosz emphasized vaccine value: "Last thing I'll say about the [influenza] vaccine is ... there are three different influenza strains that cause influenza. The vaccine covers all three, [a]nd with two of them, it looks like there's a pretty good match right now."
Dr. Pekosz emphasized that it isn't too late to receive influenza and COVID-19 vaccines, noting that vaccines require 10 to 14 days to generate protective immune responses. He particularly encouraged vaccination ahead of holiday gatherings and travel.
Vaccine Uptake Declining Across Diseases
Both COVID-19 and influenza vaccination rates have declined modestly but consistently across all age groups since the acute phase of the COVID-19 pandemic ended. "[T]he reasons driving that are very varied. Certainly, we're not seeing as big of a push to get the population vaccinated against these two illnesses as we have during the early days of the pandemic, and I think that is contributing partly to it," said Dr. Pekosz.
He stressed the continued safety and efficacy of available vaccines: "It's very clear that the COVID-19 vaccines and the influenza vaccines are safe. They do provide protection against sometimes disease, oftentimes against severe disease."
Respiratory syncytial virus (RSV) cases remain at unusually low levels, possibly because of two consecutive strong RSV seasons combined with new RSV vaccines and treatments. Nonetheless, the pattern remains unexplained.
Concerns About Federal Communication
Both experts expressed concerns about recent federal health communication. When asked about the CDC's limited public briefings on measles outbreaks, Dr. Moss stated: "The fact that we have not seen the CDC kind of out in front on these measles outbreaks is harmful, because it is withholding important information from the public, ... from health care providers, [and] from public health officials."
Dr. Pekosz acknowledged concerns about vaccine policy given statements from US Department of Health and Human Services leadership: "[W]hen an individual has some level of doubt, the first thing that ends up [happening] is inaction. So, you won't end up getting the vaccine, even if you're not necessarily an antivaccine person, because you're seeing these mixed messages."
Regarding the December Advisory Committee on Immunization Practices meeting, Dr. Moss identified "the general undermining of the process by which our current childhood immunization schedule" is developed as most concerning, noting this "sows doubt across all vaccines.".
Global Implications
Dr. Moss warned of compounding risks from reduced global health funding: "US funding cuts to some of the key global players in preventing vaccine-preventable diseases, such as the dismantling of USAID, the funding cuts to GAVI, the Vaccine Alliance, and the [WHO], ... are going to contribute to more frequent and larger outbreaks of vaccine-preventable diseases across the world, and what that's going to lead to is more frequent importations of these pathogens here into the United States."
He characterized the situation as "a perfect storm brewing for the resurgence of vaccine-preventable diseases," citing declining vaccine coverage and loosening school entry requirements alongside increasing global disease burden.
IVAC launched a measles tracker providing county-level outbreak data to help physicians and the public access information not readily available through CDC reporting.
