Every Friday, the CDC publishes a document that most Americans have never heard of but that epidemiologists consider the single most important US disease surveillance publication. The Morbidity and Mortality Weekly Report has been in continuous publication since 1952, and its pages have carried some of the earliest warnings of the deadliest outbreaks in modern American history. You can read it for free, and once you know what to look for, it takes about 10 minutes.
What is the MMWR?
MMWR stands for Morbidity and Mortality Weekly Report, and it is the CDC's primary vehicle for publishing timely, authoritative data on disease trends, unusual case clusters, and emerging health threats in the United States and its territories. Each issue contains epidemiological notes, surveillance summaries, and recommendations that reflect the CDC's current understanding of active and emerging public health events.
The publication traces back to 1952, though the CDC had been issuing weekly disease reports under other names since the late 1800s. MMWR isn't a medical journal in the traditional peer-review sense. Reports are cleared through CDC's editorial process, which prioritizes speed over the months-long review cycles of academic publications. That speed is the point.
When a new pathogen appears, when a familiar disease behaves unexpectedly, or when mortality data shifts in a way that demands attention, MMWR is usually where the CDC puts the information first.
What does an MMWR report actually contain?
A typical weekly issue includes several components. Early Release articles cover urgent public health developments that can't wait for the regular publication cycle. Regular reports present surveillance data on notifiable diseases, including weekly case counts for conditions like influenza, salmonella, and tuberculosis. Epidemiological notes describe specific outbreaks or unusual clinical findings. Policy notes outline new CDC recommendations.
The notifiable disease tables are especially useful for pattern recognition. Every week, MMWR publishes tables showing reported cases of around 80 diseases, broken down by region. You can see, at a glance, whether reported salmonella cases in the Southeast are higher than the five-year average, or whether meningococcal disease cases are clustering in a particular age group.
Numbers alone don't tell the story, though. The narrative reports are where you find context. A table might show 15 cases of listeriosis in the Midwest. The accompanying MMWR report explains that 12 of those cases are linked to a single food processing facility, that a recall has been issued, and that the case fatality rate in this cluster is 20%.
How has MMWR caught outbreaks early?
MMWR's track record includes some of the most consequential early detections in epidemiological history. On June 5, 1981, MMWR published a report describing five cases of Pneumocystis carinii pneumonia in previously healthy young men in Los Angeles. That report was the first published recognition of what became the HIV/AIDS epidemic. Five cases. One report. It changed the world.
In October 1989, an MMWR report described an unusual cluster of eosinophilia-myalgia syndrome linked to L-tryptophan supplements, triggering a recall that likely prevented thousands of additional cases.
More recently, MMWR was among the first official US publications to detail the 2014 enterovirus D68 outbreak that caused severe respiratory illness and acute flaccid myelitis in children. Early MMWR reports in January 2020 provided clinical characterization of the first US COVID-19 cases, including transmission dynamics and symptom progression, which shaped the early public health response.
The pattern is consistent: MMWR spots anomalies in US health data before they become headlines.
How do you find and read MMWR?
Access is free at cdc.gov/mmwr. No subscription needed. The current issue and full archive are available online. You can subscribe to email notifications that deliver each new issue to your inbox every Thursday evening or Friday morning.
For a quick weekly scan, focus on three things:
Early Release articles. If CDC has pushed something out ahead of the regular publication schedule, it's urgent. Read those first.
The notifiable disease tables. Look for case counts that exceed the five-year baseline. MMWR helpfully includes comparison data so you don't need to memorize historical norms. A spike in a particular disease in a particular region is your signal to pay closer attention.
Outbreak-specific reports. Skim the titles in the table of contents. Anything describing an "outbreak," "cluster," "novel," or "unusual" event gets your attention. Read the abstract and the first two paragraphs. If it's relevant to your area or your health concerns, read the full report.
You don't need an epidemiology degree to extract value from MMWR. The publication is written for health professionals, not the general public, so some of the statistical methods may be opaque. But the core findings, the summary paragraphs, the tables, and the recommendations are accessible to any careful reader. CDC also publishes "MMWR Summaries of Notifiable Diseases" annually, which give you a year-in-review perspective.
What should you watch for in MMWR?
Three specific signals in MMWR data should grab your attention:
Unusual case clusters. When MMWR describes a group of patients with a similar unusual illness in a defined geographic area or time frame, that's the early-warning signal that preceded HIV, eosinophilia-myalgia syndrome, and many other outbreak recognitions. Clusters break the expected pattern, and broken patterns are where outbreaks hide.
Rising mortality in a specific age group or region. MMWR tracks excess mortality data. When deaths from pneumonia and influenza exceed the epidemic threshold (published weekly in CDC's pneumonia and influenza mortality tracking (formerly the 122 Cities Mortality Reporting System, now part of the National Center for Health Statistics surveillance)), it's a measurable sign that something is circulating at unusual intensity.
New pathogen identification. When CDC confirms a novel virus, a new variant with different clinical characteristics, or a known pathogen in an unexpected host species, MMWR is usually the publication vehicle. The H5N1 avian influenza detections in US poultry and dairy cattle through 2024-2025 were tracked in MMWR before most media outlets covered the story.
Pair MMWR monitoring with PandemicAlarm's severity-scored global view and you have both domestic depth and international breadth. MMWR tells you what's happening inside the United States with granular detail. PandemicAlarm tells you what's approaching from outside. Together, they eliminate the major blind spots.
For more on building a complete monitoring system and understanding how WHO tracks outbreaks globally, see our pandemic preparedness guide.