COVID Antibody Testing and Booster Doses for Transplant Patients: Guidance from the Penn Transplant Institute

Male Black doctor wearing mask and shield injecting vaccine shot into female Brown patient's arm

After recent reports that some transplant recipients had better responses to the current COVID vaccines following a booster dose, the Penn Transplant Institute (PTI) offered recommendations regarding booster doses and antibody testing to the transplant community. More importantly, the PTI offered guidance for transplant recipients, their families and caregivers, to reinforce the vital importance of COVID vaccination and the necessary safeguards of illness prevention, including masking and social distancing, for these individuals.

You can find out information on the technology behind the COVID-19 vaccine, visit our mRNA Vaccines page. 

Many Questions, fewer Answers

The current emergency authorization for COVID vaccines does not allow for a booster dose. The few preliminary studies that suggested a greater antibody response in some transplant patients following a booster dose of vaccine were conducted in a small number of patients, and many questions remain.

It is unknown, for example, if it is better to use a different type of vaccine for the booster dose. We also do not know if it might be better to try to adjust a patient’s immunosuppression before a booster dose.

The response to vaccination in transplant patients is not fully understood. The body’s response to vaccine includes more than just antibody development. The body may also have a “cellular” response which cannot be measured by commercial lab tests. Thus, a patient may have a cellular response to a vaccination even if that patient does not have detectable antibodies following vaccination. Information about the cellular responses to the vaccines in these patients is limited but does suggest that antibody responses are not predictive of cellular responses; it is possible to have a cellular response in the absence of an antibody response and vice versa.

It is not yet known what level of antibody in transplant patients provides complete protection. After vaccination, protection from COVID-19 cannot be fully determined by checking a blood test for antibody. It is very possible that patients may have some protection from the vaccine even if their antibody levels are low, and their risk of getting really sick from COVID-19 is likely to be less if they are vaccinated.

What does this mean for transplant patients?

The PTI would like to ensure that booster doses are both safe and effective before recommending them. Studies relevant to booster doses are in development for transplant patients.

We would encourage all transplant patients who have not been vaccinated to be vaccinated. Information about Penn Medicine's vaccination locations is available at the Penn COVID-19 Vaccine website.

We encourage patients to make sure their family, friends, and co-workers are vaccinated. The only way we can all be protected is if everyone gets vaccinated. Children under age 12 are not yet eligible for vaccines, so it will be important to make sure they stay safe. Please recommend that parents of young children discuss COVID vaccination with their pediatricians.

Transplant patients should continue to avoid crowds and indoor gatherings with unvaccinated people unless everyone is masked, and should also continue to avoid unnecessary travel and wash their hands frequently. Please remind patients that gathering outdoors is safer than indoors and that it is safer for patients if the people they are around regularly are vaccinated.

We are not recommending routine antibody testing at this time because it is unclear what antibody titers mean. Regardless, it is our recommendation that transplant patients should be careful, even if they have detectable antibody levels.

This information has been shared with Penn Transplant patients along with a 30-minute patient webinar on this important topic. Please consider the Penn Transplant Institute a resource should questions about the COVID-19 vaccine arise.

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The Penn Physician Blog is a resource for health care professionals featuring Penn Medicine physicians and their research, innovations, programs and events. 

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