Third Dose of Pfizer's COVID-19 Vaccine Improves Protection in Organ Transplant Recipients

By Brandon May

July 07, 2021

NEW YORK (Reuters Health) - A third dose of the mRNA COVID-19 vaccine from Pfizer/BioNTech improves protection against the novel coronavirus in solid-organ transplant recipients, a population particularly vulnerable to more severe COVID-19-related outcomes, according to new study findings.

A weak immune response to two doses of COVID-19 vaccine has been observed in this population, the French research team notes in The New England Journal of Medicine. Furthermore, immunosuppressive agents may increase these patients' risk of severe COVID-19.

Dr. Nassim Kamar and colleagues at Toulouse University Hospital evaluated humoral responses to COVID-19 vaccination in 101 solid-organ recipients who received three doses of the mRNA vaccine from Pfizer and BioNTech.

Participants included 78 kidney recipients, 12 liver recipients, 8 recipients of lung or heart transplants, and 3 pancreas recipients. The mean posttransplant interval was 97 months.

Immunosuppressive regimens included glucocorticoids (87%), calcineurin inhibitors (79%), mycophenolic acid (63%), mammalian target of rapamycin inhibitors (30%), and/or belatacept (12%).

Each patient received the first two doses 1 month apart, while the third shot was given on average 2 months after the second vaccine dose. The researchers looked to see whether a third "booster" shot could improve the immunogenicity of the COVID-19 vaccine in this patient population.

Prior to the first dose, none of the participants had detectable anti-SARS-CoV-2 antibodies; before the second dose, the prevalence of antibodies was 4%. The prevalence rose to 40% prior to the third shot and was 68% four weeks after the third shot.

Approximately 44% of the 59 patients who were seronegative prior to the third dose were seropositive 1 month following the third dose; the mean antibody titer (i.e., the ratio of the sample signal to a calibrator-assigned cutoff signal) was 690.

The 40 patients who were seropositive before the additional vaccine dose were still seropositive 1 month after the third dose. In these patients, the mean titer increased from 36 prior to the third dose to 2676 approximately one month following the third shot (P<0.001).

Older age, higher levels of immunosuppression, and lower estimated glomerular filtration rate were risk factors for a lack of antibody response to vaccination.

There were no serious adverse events associated with the third dose, and COVID-19 had not developed in any patient at time of the study's publication.

Dr. Sadia Shah, Interim Medical Director for Lung Transplant Program at Mayo Clinic Arizona, who wasn't involved in the study, told Reuters Health by phone that the findings reflect her observations in her patients. "I would say half the patient population doesn't develop an antibody response despite getting the two doses of COVID-19 vaccination," she said. "And the aftermath of that is that we are seeing patients being admitted to the hospital with active COVID-19 infection despite receiving 2 doses of the vaccine."

According to Dr. Shah, it's too early to tell whether the findings from this study can be generalized to other Moderna's mRNA vaccine or other COVID-19 vaccines.

"When we start to make generalized guidelines [for COVID-19 vaccination in solid-organ transplant recipients]," she explained, "it would be important to know whether it should be the same vaccine versus a different vaccine which is proven to be more effective so the patients would know exactly what they need to do."

She added that further understanding of how a third vaccine dose works in immunocompromised patients may also help inform recommendations for other immunosuppressed patients, like those with cancer.

"Overall, I think this study will help not just with the management of organ transplant recipients but will also comparatively help a bigger patient population who might be on the same immunosuppressant," Dr. Shah said.

SOURCE: https://bit.ly/3jKxUcq The New England Journal of Medicine, online June 23, 2021.

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