Millions taking immunosuppressive medications may have a reduced response to coronavirus disease (COVID-19) vaccines, based on recent findings by clinicians at NYU Langone Health and Johns Hopkins Medicine.

Robert Montgomery, MD, chair of the Department of Surgery and the director of the NYU Langone Transplant Institute, tells CBS This Morning’s Jonathan LaPook, MD, that a number of transplant patients, who are prescribed immunosuppression drugs, had experienced severe illness at the start of the COVID-19 pandemic.

“All of these transplant patients were getting very ill, and many of them were dying,” says Dr. Montgomery, who himself is a heart transplant recipient and using immunosuppression medication. “I was very conscious that I could become one of those casualties.”

Two weeks after the second dose of the Pfizer–BioNTech COVID-19 vaccine, Dr. Montgomery was tested for antibodies, and none were found. His doctors agreed that immunosuppressants may be preventing the appropriate antibody response, so they prescribed a third vaccine dose. He was given the one-shot vaccine from Johnson & Johnson to boost his immune response.

“I am very worried transplant patients who are not aware of these (antibody test) results have a false sense of security,” Dorry Segev, MD, PhD, vice chair for research and professor of surgery at Johns Hopkins Medicine, tells CBS This Morning.

Researchers at Johns Hopkins Medicine and NYU Langone Health are currently studying the vaccine responses of patients with suppressed immune systems.

There are 10 million people with compromised immune systems in the United States.

Watch the report from CBS This Morning.