RFK Jr. claims the WI-38 cell line, utilized for growing the rubella virus in the MMR-II vaccine, originates from fetal tissue.
WASHINGTON, DC: US Health Secretary Robert F. Kennedy Jr. has asserted that the measles, mumps, and rubella (MMR) vaccine includes fetal tissue. This assertion has triggered widespread online discussions regarding the vaccine’s manufacturing process and ingredients, prompting a closer look at the facts.
Claim: RFK Jr. Asserts MMR Vaccine Contains ‘Fetal Tissue’
At his press conference today, Pennsylvania Governor Josh Shapiro accused me of promoting conspiracy theories because I told him, during an earlier telephone conversation, that some Americans had religious objections to the MMR vaccine because it contained fetal tissue. “There is…
In August 2026, US Health Secretary Robert F. Kennedy Jr. published a post on X alleging that the MMR vaccine incorporates “fetal tissue.”
Kennedy put forward this statement while responding to Pennsylvania Governor Josh Shapiro, a Democrat, who had labeled his views on vaccines as conspiracy theories.
Defending his position in an August 25 post on X, Kennedy explained that the rubella component in the MMR-II vaccine is cultivated using the WI-38 cell line. This lineage originated from lung tissue obtained from a three-month-old female fetus following a termination decades ago. He further alleged that remnants of these cells persist within each vial of MMR-II.
This is not an isolated instance of Kennedy raising such concerns. During an appearance at a NewsNation town hall hosted by Chris Cuomo on April 30, 2025, he similarly stated that the MMR vaccine is filled with “aborted fetus debris.”
Fact Check: The Statement is False
The assertion is inaccurate. Robert F. Kennedy Jr.‘s claim that the MMR vaccine retains fetal material from abortions is scientifically unfounded. This debate emerges as the United States navigates its most severe measles outbreak in decades.
According to the Centers for Disease Control and Prevention (CDC), the nation documented 2,777 measles cases between January 1 and August 20, 2026, with approximately 7% of those affected requiring hospital care.
Furthermore, the CDC noted three measles-related fatalities in 2025 and none during the tracked period in 2026. Because measles is exceptionally contagious, Harvard Medical School emphasizes that roughly 95% of the population must be immunized to maintain herd immunity and prevent outbreaks. While the US successfully sustained vaccination rates at or above that threshold for many years, coverage has experienced a decline recently.
Data from Harvard Medical School shows the national immunization rate dropped to 92% by 2023, while coverage plummeted to approximately 82% in the West Texas region where the 2025 outbreak initially flared up.
Public health professionals consistently connect misinformation and skepticism to anxieties surrounding the safety profiles of the MMR and other essential vaccines, noting that Kennedy has a history of sharing unverified or false claims regarding immunization.
To clarify, the MMR vaccine works by introducing three live, attenuated (weakened) viruses that safeguard against measles, mumps, and rubella. These weakened viruses do not induce the actual illnesses; instead, they safely prompt the immune system to recognize and build defenses against them.