How Is The Federal Government Counting Measles Deaths?

Overview

Amid the largest U.S. measles epidemic in decades, and one that threatens the country’s measles elimination status, a controversy has emerged regarding how to count deaths from measles. In August and September this year, Pennsylvania reported that four measles deaths had occurred in the state but so far, the Centers for Disease Control and Prevention (CDC) has recognized just one of these in its official measles statistics. CDC announced in early September that it would change how it counts measles deaths, no longer relying solely on reports from state health departments and instead looking to official death records as tracked by the National Center for Health Statistics (NCHS, a sub-agency within CDC). This new CDC policy of relying on NCHS-based mortality data to count measles deaths marks a departure from historical norms and processes that have accepted measles death reports from state health departments.

This Policy Watch reviews how measles deaths are typically determined, how these deaths are counted by the federal government and the role of two distinct but related federal public health surveillance systems at the center of the controversy – the CDC’s Nationally Notifiable Diseases Surveillance System (NNDSS) and NCHS’ National Vital Statistics System (NVSS). NNDSS and NVSS are separate public health surveillance systems with their own strengths and limitations: with NNDSS focused on real-time disease tracking that at times can also provide preliminary mortality information, while NVSS is focused on collecting longer-term, retrospective data on deaths and providing final determinations regarding the cause(s) of death though not necessarily designed for real-time tracking.  These two systems are complements, but one does not entirely replace the other.

Context

On August 25, Pennsylvania Governor Josh Shapiro held a press conference to announce that two deaths attributed to measles had occurred, the first such deaths in the state since 1992. As is standard protocol for cases of infectious diseases of national interest such as measles, the Pennsylvania Department of Health (PA DOH) also reported these as “measles-associated” deaths directly to CDC via the Nationally Notifiable Disease Surveillance System (NNDSS). PA DOH relied on pre-existing definitions for measles and for respiratory disease-associated mortality – which include clinical, laboratory, epidemiologic, and vital records criteria – in making the determination that these particular deaths were measles associated.

The Secretary of Health and Human Services (HHS) Robert F. Kennedy, Jr. initially objected to Pennsylvania’s classification of these deaths as measles-associated, saying Shapiro’s announcement was “premature” and suggesting the deaths “may even have been altogether fabricated.” CDC staff initially accepting the state’s death reports, though Kennedy later asked the CDC Director to remove any reference to those measles deaths on the CDC website. After the coroner in Lancaster County confirmed that measles was a contributing cause to the reported deaths, on September 4 Kennedy recognized measles as the cause for “only the second infant’s death” and stated: “The National Center for Health Statistics does not currently have any death records from 2026 that indicate measles is the underlying cause” but indicated CDC will update its measles death statistics upon receipt of such records. On September 14, a CDC spokesperson stated the agency had changed how it will count measles deaths in its official statistics, and going forward CDC would “report measles deaths if and when the National Center for Health Statistics reports measles as the underlying cause of death.”  The next day, PA DOH reported two additional measles-associated deaths, bringing the state’s own total to four. However, at present the CDC measles outbreak tally reports two deaths for 2026, with a note saying: “This number is subject to change; CDC will update its reporting as additional information becomes available and relevant reviews are completed.”

Two Systems with Different Purposes

The dispute around reporting measles deaths has brought new focus to two separate federal public health surveillance systems: the Nationally Notifiable Disease Surveillance System (NNDSS) and the National Vital Statistics System (NVSS). Each of these has a long history, dating back to the early 20^th century, but serves different purposes. These systems are described below (see Table 1). 

Nationally Notifiable Disease Surveillance System (NNDSS): Timely Case Reporting

NNDSS is a collaboration between CDC and jurisdictions across the country that supports sharing and monitoring public health information for a set of diseases and conditions of national interest. NNDSS has roots extending to a system established in 1893 by Congress for jurisdictions to report cases of disease to the Surgeon General. Over time the system expanded, with responsibility for overseeing the system transferred to CDC in 1961. Local and state public health departments have the authority and responsibility to track cases of disease, typically through reporting from health care providers, laboratories, and other sources. In turn, jurisdictions then may provide case information to CDC through NNDSS. Key characteristics of NNDSS include:

• A set of approximately 120 diseases and conditions that are designated by CDC as “nationally notifiable,” meaning the agency requests state and local health departments report to CDC when new cases of any of these conditions are identified. Measles is a nationally notifiable disease, and has been since 1912. Importantly, CDC cannot require jurisdictions to report case information, but all do, especially for high consequence infectious diseases such as measles. CDC itself says “since continuous endemic measles transmission has been eliminated, measles is an immediately notifiable disease.”
• For each NNDSS disease or condition there is a pre-established definition that jurisdictions can consult to help determine if a notifiable case has occurred. These case definitions assure a level of standardization across jurisdictions. The definitions for nationally notifiable diseases are developed in collaboration with the Council of State and Territorial Epidemiologists (CSTE) and intermittently updated and refined. The current NNDSS case definition for measles dates to 2013.
• Jurisdictions determine the extent of detail provided in their reports. Information shared through NNDSS is “de-identified” (i.e. with personally identifying information removed), but jurisdictions may include demographic, clinical, and epidemiologic characteristics and the course of clinical illness (including whether death occurred) in their case reports.
• NNDSS reports can preliminarily indicate the cause of death in a particular case, but are not expected or designed to be a final determination. For this reason, Pennsylvania has reported the four deaths as being “measles-associated” rather than presenting a final determination of measles as the cause of death. The NNDSS definition for measles does not include specific guidance for when and how to report a death as being caused by measles infection, though CDC reports it is working with CSTE to update the definition “to promote consistent classification and reporting of measles deaths across jurisdictions.” 
• A relative strength of NNDSS is the ability for rapid communication of case-level epidemiologic information between jurisdictions and the CDC, which can allow for near real-time tracking of outbreaks and disease trends. A limitation is that rapidly reported information may only be preliminary in nature, and case reports could be incomplete or lacking in detail.

National Vital Statistics System (NVSS): Comprehensive Cause of Death Reporting

NVSS is the federal government’s primary mechanism for tracking mortality (and other vital statistics) data. The NVSS has roots going back to 1902, when Congress created a permanent Census Bureau and authorized the government to obtain copies of state vital records. By 1933, all states were required to record births and deaths and provide data to the Census Bureau. The NCHS was created in 1960, with responsibility for federal vital statistics transferred there.  The responsibility and legal authority for documenting births, deaths, and other vital statistics resides at the state and local level, but by statute NCHS has authority to collect and review these data – each state has a contract with NCHS that allows the federal government access to this information to produce national vital statistics. Key characteristics of NVSS include:

• Housing the most complete set of data on deaths and births in the U.S. Death certificate information captured through NVSS is the most comprehensive source for mortality information nationally.
• Death certificate information captured through NVSS is considered the benchmark for cause of death data. When completing a death certificate, a provider must include the best and final judgement on the proximate cause(s) of death as well as potential other factors that may have contributed to the death. Information from an autopsy, or laboratory and other test results may be included. Demographic details are also reported through the system such as age, sex, race/ethnicity, and education.
• Nuances regarding a possible chain of events leading to a death and potentially multiple contributing factors can introduce complexity in cause of death determinations. Regarding the Pennsylvania cases, there has been some debate about measles being a primary cause of the deaths reported by the PA DOH, especially in relation to one of the initial reported deaths – a newborn infant that died from a lacerated spleen but was also positive for measles. 
• State/local vital records offices are responsible for inspecting death certificates for timeliness, completeness, and accuracy of information, processing, and storing the records. Data files derived from these state/local records are then transmitted to NCHS.
• NCHS reviews and processes vital statistics data and codes mortality statistics according to the current revision of the International Classification of Diseases (presently ICD-10, which the U.S. began to use in 1999). ICD-10 provides definitions and rules for selecting the underlying cause of death when generating vital statistics through NVSS. Typically, NVSS will release “provisional” cause of death data with a 3 to 9 month lag (depending on the cause of death), though full provisional data may take up to one a year to be released. Final cause of death data is made available after about two years. For example, the most recent NVSS provisional cause of death data are for 2025 while the most recent final cause of death data are from 2024. In special circumstances, provisional death data can become available even earlier – for example, during the COVID-19 pandemic NVSS provided updated COVID-19 related death statistics on a weekly basis.
• A relative strength of the NVSS is its completeness and the comprehensiveness of its cause of death information. A relative weakness of the NVSS is the time lag between when deaths occur and the availability of cause of death data.