Cancer survivor shares how stem cell transplant reset her immune system

Hodgkin lymphoma survivor Amelia Sullivan says a life-saving stem cell transplant not only helped cure her cancer but also reset her immune system to a point where she temporarily became “completely unvaccinated,” leaving even minor illnesses feeling dangerous during recovery.

Sullivan, now 22, was diagnosed at age 20 in 2023 after months of chest pain, shortness of breath, and elevated heart rate were found to be caused by tumors pressing against her trachea, heart, and arteries. 

After initial chemotherapy led her into remission in March 2024, she later relapsed and underwent a stem cell transplant on March 10, 2025.

The procedure, which replaces diseased stem cells with healthy ones, is used to treat certain cancers and blood disorders. But Sullivan says the treatment also erased the immune system she had built over two decades, including all prior childhood vaccinations and natural immunity.

“Because it's not possible to just get rid of bad cells, they had to eliminate my healthy stem cells,” Sullivan told People. “Which, in essence, erased my entire immune system.”

Doctors later reintroduced her previously harvested stem cells to rebuild immunity, but the recovery process proved long and unpredictable. 

At one point, Sullivan developed engraftment syndrome, a serious inflammatory reaction that required intensive care support.

She described the experience as a stark reversal: “It’s ironic that what eventually saved my life almost killed me first.”

During recovery, Sullivan was placed under strict medical precautions, including avoiding crowds, travel, and certain foods due to extreme vulnerability to infection. Even routine activities became high-risk, as her immune system gradually restarted from scratch.

Flu season proved particularly difficult. Sullivan said she contracted multiple illnesses, including two strains of influenza at once, and experienced prolonged recovery times that were far more severe than typical cases.

“The common cold felt like life or death in my shoes,” she said. “Imagine a newborn having the flu; it's no different than my situation.”

As her immune system slowly rebuilt, Sullivan began restarting her vaccination schedule. In April 2026, she received seven vaccines in a single day, with more doses scheduled for later in the year.

She described the process as emotionally significant, marking both progress and a reminder of what she endured. “Getting my vaccines again was a big milestone,” she said. “But also a reminder of what I went through.”

Despite the challenges, Sullivan says she views the recovery process as part of her broader healing journey.