In the week after Pennsylvania reported its first measles deaths in 35 years, controversy erupted as anti-vaccine activists and some public officials raised questions over whether the patients died from measles or happened to have the virus when they died from something else.

The conflict has centered around one of the deaths, a newborn who tested positive for the virus and died shortly after childbirth. The infant’s mother also tested positive for measles, said Dr. Stephen Diamantoni, the Lancaster County coroner, in an interview. A forensic pathologist performed an autopsy and determined that the immediate cause of death was a lacerated spleen, he added. Neil Ruhland, a spokesman for the Pennsylvania Department of Health, said that as the body responds to a measles infection, the spleen can become enlarged, making it more vulnerable to injury and rupture.

The deaths set off a public battle between Pennsylvania’s Democratic governor, Josh Shapiro, and Robert F. Kennedy Jr., the nation’s health secretary.

In a news conference on Tuesday announcing the deaths, Mr. Shapiro accused Mr. Kennedy of contributing to the state’s measles crisis by spreading misinformation.

The next day, Mr. Kennedy shot back on X, claiming that the measles deaths in Pennsylvania “may have even been altogether fabricated by one of the Governor’s hopeful staffers.”

In a statement posted on X, Dr. Debra Bogen, Pennsylvania’s health secretary, defended the department’s announcement, writing that she has “thoroughly reviewed the case investigation” and “sadly can confirm that there were two recent measles-associated deaths.”

But the Centers for Disease Control and Prevention released a statement applauding Mr. Kennedy’s “efforts to clarify conflicting information from Pennsylvania officials about whether the two reported deaths were caused by measles.”

The statement added, “C.D.C. is working to determine what actually occurred.”

Further complicating matters, Dr. Diamantoni, a Republican who was last elected county coroner in 2023, said the pathologist who performed the autopsy did not determine measles to be a cause of death nor did he find evidence of an enlarged spleen.

Mr. Ruhland said that in a measles-related death, the virus is not necessarily listed as the immediate cause of death, even though the infection may be a contributing factor. He compared it to a death from a drug overdose: The immediate cause of death may be respiratory or cardiac failure, but the overdose contributed.

Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, said this discourse over whether someone died from an infection or with an infection is a common talking point within anti-vaccine circles that cropped up during the Covid-19 pandemic, as a way to downplay the seriousness of the illness.

Several prominent figures in anti-vaccine circles also latched onto the phrase “measles-associated deaths,” which they suggested health officials were using to hide the fact that the virus did not play a role in the reported deaths.

“The difference between a measles-associated death and a death due to measles is pretty semantic,” said Dr. Andrew Pavia, a pediatric infectious disease specialist in Utah, adding that people “tie themselves up in knots” trying to avoid attributing a death to measles.

Based on the limited details released, several of the top measles researchers in the country said the virus very likely played a role in the newborn’s death. Measles stresses the body in a multitude of ways, and would be especially taxing in a case like this, where the infant appears to have contracted the virus from its mother in the womb shortly before birth, Dr. Pavia said.

“It’s hard to imagine that measles was not a major contributing factor,” he said.

Still, doctors and public health officials have been frustrated by the scant details provided by the state health department, which they said have made it difficult to understand what happened and have allowed misinformation and rumors to run rampant. Experts pointed to other health departments as a model, like the Texas Department of Health, which immediately disclosed last year that a “school-aged” child had died of measles after being hospitalized for complications.

Initially, the Pennsylvania Department of Health declined to provide any details about the ages of the patients or the cause of the deaths, citing privacy concerns. Rumors and disinformation quickly filled the vacuum.

Before details of the infant’s death were revealed, Ginger Taylor, recently appointed by Mr. Kennedy to serve on a federal autism research panel, posted an image of a fabricated news headline, which claimed that the two patients were 87- and 89-year-old men. The Pennsylvania chapter of the anti-vaccine group Children’s Health Defense — which Mr. Kennedy founded and led for many years — suggested that the deaths might be related to an uptick of vaccination in the area.

The state health department has not released any additional details about the second death. Referring to the families of the victims, Dr. Bogen said in her statement on X that she would continue to do “everything in my power to protect their confidentiality.”