Mike Willis was intrigued when he heard about a study aimed at determining the effectiveness of a third dose of COVID-19 vaccine boosters for transplant recipients.
As a heart transplant patient who takes an immunosuppressant medication every 12 hours, Willis said the opportunity to boost his protection against COVID-19 made it easier for him to volunteer.
“I didn’t have any antibodies after two doses,” the 66-year-old said, adding that he was pleased to learn that the double-blind study gave him a third dose instead of a placebo. “So anything [is] higher than nothing.”
The results released Wednesday suggest that a third booster dose is the “best way to increase protection” in transplant recipients, say researchers at the University of Toronto Health Network (UHN), who led the study.
Since the highly transmissible delta variant is driving cases in parts of the country, they say there is a more urgent need to ensure that transplant patients, who often do not respond adequately with a normal two-dose series, can enhance their protection.
“As I see it, there are transplant patients who are completely unprotected at the moment, despite having taken two doses,” said Dr. Deepali Kumar, director of UHN’s Division of Transplant Infectious Diseases and senior author of the study.
“If we can give them a third dose to have a better chance of protection, I think we should.”
The study, published in the New England Journal of Medicine, looked at levels of different types of antibodies as well as T-cell responses in 120 Ontario transplant patients and found increases in the majority of those who received a third vaccine dose.
UHN said the study is the first randomized, placebo-controlled trial of COVID-19 boosters in transplant patients. The researchers compared 60 participants who received a third dose of the Moderna vaccine with 60 people who received a placebo.
Previous studies, including one from the US earlier this summer, suggested that third doses could amplify immune responses in some transplant patients, but they did not include a control group.
“It’s really hard to tell if something is working unless you do it,” said Dr. Atul Homar, medical director of the Ajmera Transplant Center and another co-author of the study.
“We’ve seen data that there may have been a benefit, but I think this is the definitive study that shows a clear benefit.”
On Wednesday, the Ontario Department of Health said it would “continue to actively review the evidence and provide updated guidance as needed.”
All study participants were fully vaccinated with Moderna and none had previous COVID-19 infection. Half of the participants received a third dose of Moderna two months after the second dose.
Just over half, or 55 percent, of those who received a third dose reported an antibody response rate of at least 100 units per milliliter, compared with 18 percent for the placebo group.
Previous modeling suggested that 100 units “might be protective,” Kumar said. In healthy people, antibody levels after the two doses typically reach 1,000 to 10,000 units per milliliter, Kumar said, and some participants in the transplant study showed similar numbers.
“It was actually very exciting,” she said. “We were able to get a significant immune response with a third dose.”
Kumar added that those who did not reach the 100-unit standard could still boost protection after a third dose.
The study also found that 60 percent of the three dose group developed neutralizing antibodies that help identify the COVID-19 virus. T-cell responses, which help the immune system ward off severe disease, were also more robust in the three dose group.
Mild side effects
Kumar said only mild side effects have been reported with the booster.
Moderna was chosen because the vaccine contains a higher dose than the Pfizer-BioNTech vaccine, Kumar said, adding that previous studies of the efficacy of the flu vaccine indicate that the flu vaccine at higher doses was more successful in transplant patients.
She said more studies would be needed to see how Pfizer recipients responded. A national study by the same UHN team will look at blood samples of transplant patients who received either Pfizer or Moderna as a third dose.
“I think in theory [Pfizer] “He will have a similar response but it will be difficult to say without a head-to-head comparison,” Kumar said.
While Willis’ antibody levels rose significantly after Moderna’s third shot, he said it’s possible he’s not quite as protected as
A healthy person takes two doses.
Willis gained his new heart in 2015 after developing myocarditis, which is scarring of the heart muscles, after a previous viral infection. He’s had to be careful about exposing his weakened immune system to pathogens ever since.
The retiree from Guelph, Ont., said he is still following usual safety measures such as physical distancing and wearing masks,
Especially indoors with strangers. But when he’s with people he knows who have been fully vaccinated, he can feel much more comfortable.
Like many transplant patients, Willis relies on those around him to vaccinate themselves to reduce the chance of him being exposed to the virus.
He said, “If it weren’t for that, I might be a hermit.”