HARRISBURG, Pa. – Robert F. Kennedy Jr. is publicly firing back at Pennsylvania Gov. Josh Shapiro after the two officials clashed over the MMR vaccine, declining vaccination rates and Kennedy’s statements about the vaccine’s connection to fetal-derived cell lines.
The dispute erupted after Shapiro held a Tuesday news conference addressing Pennsylvania’s measles response following the state’s first measles-associated deaths in 35 years. Shapiro criticized Kennedy’s vaccine messaging, while Kennedy responded hours later with a lengthy post accusing the Democratic governor of misrepresenting what he had told him during a previous telephone conversation.
At the heart of the dispute is an important distinction. The MMR vaccine does not contain intact fetal tissue, but the rubella component of Merck’s M-M-R II is manufactured using WI-38 human diploid lung fibroblast cells, a cell line originally developed from fetal tissue obtained decades ago. Kennedy argues that connection creates religious objections for some Americans.
- Kennedy says Shapiro misrepresented his comments about the MMR vaccine’s historical connection to fetal-derived cell lines.
- Shapiro has accused Kennedy of spreading vaccine misinformation as Pennsylvania responds to a measles outbreak and falling vaccination rates.
- The dispute centers partly on the difference between saying a vaccine contains fetal tissue and saying a vaccine is manufactured using a decades-old fetal-derived cell line.
Kennedy Says Shapiro Got the MMR Argument Wrong
Kennedy said the disagreement began during a telephone conversation in which he told Shapiro that some Americans have religious objections to the MMR vaccine because of its connection to fetal tissue.
According to Kennedy, Shapiro responded by telling him, “There is no fetal tissue in the MMR.”
Kennedy then publicly challenged Shapiro’s characterization of their conversation.
“At his press conference today, Pennsylvania Governor Josh Shapiro accused me of promoting conspiracy theories,” Kennedy wrote.
Kennedy pointed to the history of WI-38, a human diploid cell line used in producing the rubella component of M-M-R II.
Merck’s prescribing information confirms that the rubella virus used in M-M-R II is propagated in WI-38 human diploid lung fibroblasts. The vaccine’s measles and mumps viruses are grown using chick embryo cell culture instead.
That distinction matters when evaluating the competing claims.
Saying the vaccine contains “fetal tissue” can leave the impression that pieces of fetal organs or tissue are present in the injection. That is not an accurate description of the finished MMR vaccine.
But saying there is no historical connection to fetal-derived cells would also miss an important part of how the rubella vaccine was developed and continues to be manufactured.
RFK Jr. Points to Stanley Plotkin Deposition
Kennedy also posted footage from a deposition involving vaccine researcher Dr. Stanley Plotkin, a major figure in the development of the rubella vaccine.
Kennedy cited the testimony while making a broader argument about the use of aborted fetal tissue in historical vaccine research.
He also highlighted testimony concerning residual cellular DNA in vaccines manufactured using human cell substrates.
Kennedy claimed that M-M-R II contains approximately 150 nanograms of residual cell-substrate DNA per dose and then converted that amount into what he described as hundreds of billions of DNA fragments.
The presence of residual DNA from cell substrates is different from saying a vaccine contains fetal tissue. Those terms describe different things, and the distinction is particularly important in a debate involving vaccines, religion and public health.
Kennedy’s larger point was that Americans with moral or religious objections to abortion may also object to vaccines developed or manufactured using cell lines historically derived from aborted fetal tissue.
The controversy is not new. Religious organizations have wrestled with that ethical question for decades, often distinguishing between the original abortion and the continued use of descendant laboratory cell lines many years later.
Shapiro Blames Vaccine Decline for Measles Concerns
The argument comes amid a serious measles problem in Pennsylvania.
State health officials announced Tuesday that Pennsylvania had recorded its first measles-associated deaths in 35 years. The Shapiro administration has responded by expanding vaccination clinics and encouraging residents to receive the MMR vaccine.
Pennsylvania officials say two doses of the MMR vaccine provide approximately 97% protection against measles.
Shapiro has also pointed to declining vaccination rates as part of the problem.
Kennedy disputed the suggestion that he was responsible for Pennsylvania’s decline.
“Governor Shapiro also faulted me for the decline in Pennsylvania vaccination rates from 97% – 93.2%,” Kennedy wrote.
Kennedy said that when he challenged Shapiro on the timeline, the governor acknowledged that much of the decline occurred before Kennedy took control of the Department of Health and Human Services.
Kennedy blamed declining public confidence in vaccination programs partly on the government’s conduct during the COVID-19 pandemic.
“It’s unfortunately true that the government lockdowns, deceptions, manipulation, and overreach during Covid severely damaged public faith in the vaccine program,” Kennedy wrote.
Kennedy Accuses Shapiro of ‘Gaslighting’
The exchange quickly moved beyond a technical argument about vaccine manufacturing.
Kennedy accused Shapiro of publicly labeling him a source of misinformation without providing a specific example during their private conversation.
“When I asked him for an example, he was unable to provide one,” Kennedy wrote.
Kennedy said Shapiro nevertheless repeated the accusation during his news conference.
“Governor Shapiro’s press conference was an example of the same species of gaslighting,” Kennedy said.
The Trump administration, Kennedy argued, is trying to rebuild confidence in federal health agencies through greater transparency rather than simply demanding that Americans trust government recommendations.
“The Trump administration is working to restore public trust not by gaslighting or manipulating, but by being truthful, at last, with the public,” Kennedy wrote.
The argument is likely to continue because it involves two separate questions that are frequently combined in political debate.
One is whether the MMR vaccine is effective at preventing measles. Pennsylvania health officials and federal regulators say that it is, and the FDA continues to license M-M-R II for prevention of measles, mumps and rubella.
The other is whether Americans should be told clearly about the historical and continuing role of fetal-derived cell lines in the development and production of some vaccines.
For Kennedy, that distinction is central to his argument that public confidence is built through disclosure rather than dismissal.
Does the MMR vaccine contain fetal tissue?
Not in the ordinary meaning of intact fetal tissue. However, the rubella virus used in Merck’s M-M-R II is grown using WI-38 human diploid lung fibroblasts, a laboratory cell line originally derived from fetal tissue decades ago.
Why are Robert F. Kennedy Jr. and Josh Shapiro fighting over the MMR vaccine?
Kennedy says Shapiro misrepresented his comments about religious objections to fetal-derived cell lines, while Shapiro has criticized Kennedy’s vaccine messaging as Pennsylvania confronts measles cases and declining vaccination rates.
How effective is the MMR vaccine against measles?
Pennsylvania health officials say two doses provide approximately 97% protection against measles and are encouraging vaccination as the state responds to its current outbreak.
Sources: Robert F. Kennedy Jr. statement; Pennsylvania Department of Health; FDA M-M-R II information; Merck M-M-R II prescribing information; Stanley Plotkin deposition excerpt provided by Kennedy.
