June 16, 2021 -- A third dose of a COVID-19 vaccine can boost antibody levels in people who previously received an organ transplant, according to data from a newly published case series.

All of those with low levels of antibodies before the third dose had higher levels after receiving the additional shot, according to the paper, published in Annals of Internal Medicine.

Researchers at Johns Hopkins University in Baltimore, who keep a COVID-19 vaccine registry, perform antibody tests on all patients and inform them of their results. Patients were asked to tell the research team if they received a third dose, and, the research team tracked the immune responses of those who did.

The participants in this case series had low antibody levels and received a third dose of a vaccine on their own between March 20 and May 10.

Third dose results

In this cases series – thought to be the first to look at third vaccine shots in this type of patient group – all six of those who had low antibody levels before the third dose had high levels after the third dose.

But Of the 24 people who had extremely low levels of antibodies before the third dose, just six had high levels after the third dose.

“Several of those boosted very nicely into ranges seen, using these assays, in healthy persons,” said William Werbel, MD, a fellow in infectious disease at Johns Hopkins, who helped lead the study.

“The benefits at least from an antibody perspective were not the same for everybody and so this is obviously something that needs to be considered when thinking about selecting patients” for a COVID-19 prevention strategy, he said.

Negative reactions to the vaccine were in the low to moderate range, such as some arm pain and fatigue.

“Showing that something is safe in that special, vulnerable population is important,” Werbel said. “We’re all wanting to make sure that we’re doing no harm.”

Werbel noted that there was no pattern in the small series based on the organ transplanted or in the vaccines used. As their third shot, 15 of the patients received the Johnson & Johnson vaccine; nine received Moderna; and six received the Pfizer vaccine.

Welcome news, but larger studies needed

“To think that a third dose could confer protection for a significant number of people is of course extremely welcome news,” said Christian Larsen, MD, professor of surgery in the transplantation division at Emory University in Atlanta, who was not involved in the study. “It’s the easiest conceivable next intervention.”

He added, “We just want studies to confirm that – larger studies.”

Werbel stressed the importance of looking at third doses in these patients in a more controlled fashion in a randomized trial, to more carefully monitor safety and how patients fare when starting with one type of vaccine and switching to another, for example.

Richard Wender, MD, chair of family medicine and community health at the University of Pennsylvania, said the findings are a reminder that there is still a lot that is unknown about COVID-19 and vaccination.

“We still don’t know who will or will not benefit from a third dose,” he said. “And our knowledge is evolving. For example, a recent study suggested that people with previous infection and who are vaccinated may have better and longer protection than people with vaccination alone. We’re still learning.”

He added that specialists, not primary care doctors, should be relied upon to respond to this emerging vaccination data. Primary care doctors are very busy in other ways – such as in getting children caught up on vaccinations and helping adults return to managing their chronic diseases, Wender noted.

“Their focus needs to be on helping to overcome hesitancy, mistrust, lack of information, or anti-vaccination sentiment to help more people feel comfortable being vaccinated – this is a lot of work and needs constant focus. In short, primary care clinicians need to focus chiefly on the unvaccinated,” he said.

“Monitoring immunization recommendations for unique at-risk populations should be the chief responsibility of teams providing subspecialty care, [such as for] transplant patients, people with chronic kidney disease, cancer patients, and people with other chronic illnesses. This will allow primary care clinicians to tackle their many complex jobs.”