Patients with cancer have shown varying responses to COVID-19 vaccination, with good responses in patients with solid tumors (even while on systemic therapy) and poor responses in patients with blood cancers, particularly those on immunosuppressive therapies.
The data are evolving to show factors associated with a poor response but are not strong enough yet to recommend booster shots, say researchers.
The work is defining who will likely need a COVID vaccine booster when they become available. “It’s definitely not all cancer patients,” said Dimpy Shah, MD, PhD, a cancer epidemiologist at the Mays Cancer Center, University of Texas, San Antonio.
Public anxiously awaiting boosters
Boosters aren’t recommended in the United States at the moment, in large part because the Emergency Use Authorization under which the vaccines are being administered allows for only two shots of the Pfizer and Moderna vaccines and one shot of the Johnson & Johnson vaccine.
Even so, regulators and policymakers are “keenly aware that physicians and patients alike are anxious to get going and start doing boosters,” Dr. Shah said. There’s concern that antibody response might wane over time, perhaps even more quickly in patients with cancer.
Pfizer is already in talks with the U.S. Food and Drug Administration to authorize a third dose of its vaccine in the United States. Guidelines could very well change in coming months, said Ghady Haidar, MD, a specialist in infectious diseases and cancer at the University of Pittsburgh.
However, it’s still early in the game, and it’s not clear yet if boosters are necessary in cancer, Dr. Haidar said in an interview.
For one thing, it’s unknown if poor antibody response really means that patients aren’t protected, he explained. The vaccines elicit T-cell responses that could protect patients regardless of antibody levels. It’s also unclear if antibody titer levels are clinically relevant, and there hasn’t been much indication yet that less-than-robust vaccine responses translate to worse COVID outcomes in patients with cancer.
Those and other questions are areas of active investigation by Dr. Shah, Dr. Haidar, and others. Dozens of clinical trials are investigating vaccine response in patients with cancer, including the use of boosters.
Meanwhile, some cancer patients aren’t waiting around for more study results. “I get many, many emails a day” about booster shots, Dr. Haidar said. “We recommend against” them for now but some people bend the rules and get an extra shot anyway. “I get it. People are apprehensive.”
Three COVID deaths despite full vaccination
The vaccine clinical trials had fewer patients with cancer, so researchers are moving fast to backfill the data. Although there is some variation in what’s being reported, an overall picture is slowly emerging.
Dr. Shah and her team reported on responses to the mRNA COVID vaccines from Pfizer and Moderna and found a 94% seroconversion rate in 131 patients with cancer 3-4 weeks after their second dose of vaccine. They also found good responses among patients on cytotoxic chemotherapy within 6 months of their first vaccine dose, although their antibody titer levels were significantly lower than seen in other patients with cancer.
Investigators from Montefiore Medical Center in New York City also recently reported a 94% seroconversion rate among 200 patients with cancer, including 98% seroconversion in patients with solid tumors. Rates were lower in patients with blood cancers but were still 85% overall, with 70% conversion among patients on anti-CD20 therapies and 73% among stem cell transplant patients.
Dr. Haidar’s group reported a seroconversion rate of 82.4% among patients with solid tumors but only 54.7% among those with blood cancer. Risk factors for poor response included treatment with antimetabolites and anti-CD20 therapies, and, in the solid tumor group, radiation therapy, likely because of its overall toxicity and impact on lymphocyte function.
Israeli investigators reported in May a 90% seroconversion rate after two doses of the Pfizer vaccine among 102 patients with solid tumors on active treatment, which compared favorably to the 100% conversion rate in healthy controls, but they noted that antibody titers were considerably lower in patients with cancer.
The only variable associated with lower titer levels was combined use of chemotherapy and immunotherapy, they noted. There were also three women on dose-dense chemotherapy for breast cancer who did not produce any antibodies.
In a study limited to patients with blood cancers, a Lithuanian team recently reported that among 885 patients, those on Bruton tyrosine kinase inhibitors, ruxolitinib (Jakafi), venetoclax (Venclexta), or anti-CD20 therapies mounted almost no antibody response to the Pfizer vaccine.
The Lithuanian group also reported nine breakthrough COVID infections among their fully vaccinated blood cancer patients, including three deaths.
A team from the Icahn School of Medicine at Mount Sinai, New York reported that more than 15% of 260 patients with multiple myeloma also had no response to the Pfizer or Moderna vaccine; they were on BCMA-targeted therapy or anti-CD38 monoclonal antibody therapy at the time of vaccination, but a few had undergone CAR-T cell therapy more than 3 months beforehand.