Vaccines are offered in Chula Vista. Photo by Chris Stone

Researchers at UC San Diego Health Thursday began a pair of clinical trials to study COVID-19 vaccinated organ and bone marrow transplant recipients to monitor immune response to the virus.

Evidence that innoculation against COVID-19 – most notably with the Pfizer and Moderna vaccines – produces robust, durable protection in most recipients, questions remain for donor patients, whose immune systems are suppressed to ensure their transplants are successful.

Some studies have found that vaccinated transplant recipients produce a weak immune response, and severe cases of COVID-19 have been reported among recipients who had received two doses of vaccine.

“Our goal is to quantify the (immune response) of COVID vaccines in immunocompromised populations,” said Dr. Jennifer Dan, an infectious disease specialist at UCSD Health. “We want to gain an understanding of how differing degrees of immunosuppression may impact the COVID vaccine immune response and use that knowledge to optimize vaccine regimens for these patients.”

Under current guidelines, heart, lung, liver and kidney recipients, along with bone marrow recipients are eligible for COVID-19 vaccination.

In the case of bone marrow, recipients can begin receiving COVID-19 vaccinations three months after transplant. Organ recipients may be vaccinated as early as one month after transplantation, although a strong immunosuppression drug regimen to prevent organ rejection may cause a delay.

In both cases, the patients’ transplant physicians determine when the vaccination process begins.

Both clinical trials are currently enrolling participants whose transplant procedures can be relatively recent or years in the past. Dan said she expects more recent recipients are likely to produce a weaker immune response from vaccination.

“For instance, if a (bone marrow) recipient is four months post-transplantation, that person may not produce as good of an immune response as someone who is two years post-transplantation,” she said. “This has to do with the pace of how the immune system is reconstituted following transplantation.

“For solid organ transplant recipients, the amount of immunosuppression will likely dictate if a person makes a good response to the COVID vaccine,” she continued.

Dan hopes to enroll 200 organ transplant recipients and 200 bone marrow recipients.

The trials involve a sequence of blood draws.

“Ideally, we want to get a pre-vaccination blood specimen,” said Dan. “However, we have been enrolling patients who have already started the vaccination series.

Immune response is measured by the presence and quantity of neutralizing antibodies and T-cells, both key players in the immune system’s response to foreign bodies, such as viruses and bacteria.

The trials will primarily enroll UC San Diego Health patients, but any qualifying person can participate through the UC San Diego Altman Clinical and Translational Research Institute.

For more information about the trials or to enroll, contact clinical research coordinators:

  • Yasmeen Esshaki, 858-822-2908,
  • Marielys Padilla-Martinez, 858-534-4449,
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