Study suggests 94 per cent of cancer patients develop COVID-19 antibody response after full vaccination

TORONTO -- A new international study suggests that 94 per cent of cancer patients experienced an immune response after being vaccinated with either Pfizer or Moderna — but it only became a strong response after a second dose, reiterating the importance of cancer patients receiving both doses.

How effective vaccines are for those who are undergoing cancer treatments has been a source of concern and confusion throughout the pandemic, as vaccines for other diseases have been known to have different impacts on cancer patients.

But according to this U.S. and Swiss study, published in June in the journal Cancer Cell, by the time a cancer patient has received both doses, they largely receive a similar level of protection as the general population, with some exceptions.

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The study looked at a total of 131 patients, who were given either the Pfizer-BioNTech vaccine or the Moderna vaccine. The study followed up with participants around 22 days after their second dose. There was no extended delay in between the doses, as has been seen in some regions. 

Out of these 131 patients, only seven high-risk patients did not develop an antibody response after being vaccinated. The study did not look at other aspects of the immune response, such as T-cells.

"We could not find any antibodies against the virus in those patients," Dimpy P. Shah, assistant professor at UT Health San Antonio and one of the authors of the study, said in a press release. "That has implications for the future. Should we provide a third dose of vaccine after cancer therapy has completed in certain high-risk patients?”

This study confirmed the results of earlier ones that had found that cancer patients receive a lower level of protection from one shot alone when compared to the general public. In this new study, they found the immune response was significantly lower in the participants after the first dose compared to after the second dose, which points to the need for patients to remain cautious in the waiting period between their first and second dose.

"They still need to have that awareness that they could potentially be at risk because their body has not responded to vaccination," Shah said.

But overall, a high percentage of patients achieved a positive immune response once fully vaccinated.

"We observed a significant difference in response when two doses were given," Shah said. "At least for patients with cancer, two doses are very important for robust antibody response.”

The question of vaccination for cancer patients is important because if a cancer patient contracts COVID-19, they are more likely to have complications or even die of the virus.

Another recent study from May, which attempted to investigate this issue, found that around 90 per cent of cancer patients out of 102 participants developed an antibody response to the Pfizer vaccine after two doses, compared to 100 per cent of a control group of 78 non-cancer patients. The concentration of antibodies was lower in the cancer patients than in the control group, with the lowest concentration observed in those receiving chemotherapy plus immunotherapy.

In the new June study, antibody levels were higher in women than in men, but there was not a significant difference between the effect of the two different vaccines used.

More than 80 per cent of the participants had a solid cancer, with breast and urological cancer being the most common, while 19 per cent had hematological malignancy, which is cancers that affect the blood, bone marrow and lymph nodes. Antibody levels were significantly lower in those who had blood cancers as opposed to those with solid tumours.

Five of the patients who developed no response to the vaccine had hematological malignancy.

But the reason some did not respond may also have to do with the cancer interventions they were receiving, or had recently received.

Patients receiving endocrine therapy or who were only under clinical surveillance and receiving no treatment had the best outcomes, achieving a higher immune response. Two-thirds of the patients had received some form of therapy within six months of their vaccination, with 23 per cent receiving cytotoxic chemotherapy, 15 per cent receiving endocrine therapy, 13 per cent receiving monoclonal antibody therapy, and 11 per cent receiving kinase inhibitor therapy and immunotherapy respectively.

“Significant difference in antibody response was noted between the various anti-cancer treatment modalities,” the study noted.

Lower levels of antibody concentration was observed in those receiving cytotoxic chemotherapy and monoclonal antibody therapy. Four patients receiving a monoclonal antibody therapy called Rituximab within six months of vaccination were among the seven who showed no response to the vaccine.

Cytotoxic chemotherapy was also correlated with a more muted antibody response.

"How that relates to protection against COVID-19, we don't know yet," Shah said.

The study was limited by the amount of patients, as well as the fact that 80 per cent of the participants were white.

“We recommend that future studies be done in Black, Asian and Hispanic patients, as well, to see if there are any differences in vaccination immune response," Dr. Ruben Mesa, executive director of the Mays Cancer Center and a study author, said in the release.

The fact that cancer patients do develop an antibody response, indicating that they have received some protection against the virus, is positive news even if vaccines are slightly less effective for them. Although some vaccinated people have contracted the virus, vaccination has been shown to fight hospitalization and severe cases of COVID-19 in the rare event that a person still catches it.