Scientists at the University Health Network (UHN) here have conducted a first-in-the-world randomised placebo-controlled trial of third dose Covid-19 booster vaccine for transplant patients that shows substantially improved protection.

Persons who have received an organ transplant are considered to be at increased risk for Covid-19 and for a severe outcome because their immune systems are necessarily suppressed to ensure their transplants are successful and lasting.

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The study, published in the New England Journal of Medicine, has shown that the third dose of the Covid vaccine is the best way to increase protection in them.

The team enrolled 120 transplant patients between May 25 and June 3. None of them had Covid previously and all of them had received two doses of the Moderna vaccine. Half of the participants received a third shot of the vaccine (at the 2-month mark after their second dose) and the other half received placebos.

The primary outcome was based on antibody level greater than 100 U/ml against the spike protein of the virus. In the placebo group — after three doses (where the third dose was placebo), the response rate was only 18 per cent whereas in the Moderna three-dose group, the response rate was 55 per cent.

“This is an important win for our patients because the results are quite conclusive,” said Dr Atul Humar, Medical Director of the Ajmera Transplant Centre, UHN.

“The third dose was safe and well-tolerated and should lead to a change in the practice of giving third doses to this vulnerable population,” he added.  In addition, 60 per cent of the patients in the Moderna group also developed neutralising antibodies versus 25 per cent in the placebo group.

There was also a substantial improvement in the ability of the three-dose Moderna group to allow the patients to develop a robust T-cell response against the virus.

Moreover, the third booster vaccine was found to be very well tolerated with only mild side effects and did not cause acute organ rejections — an important finding, as there were concerns that repeated vaccinations could increase the incidence of organ rejection in transplant recipients, the researchers said.