People with blood cancers are at a higher risk than healthy individuals for severe and life-threatening COVID-19 illness; furthermore, research suggests that they do not always achieve optimal protection from vaccination. A new Blood study, the first to report on post-vaccination COVID-19 cases in patients with blood cancer, offers preliminary findings about the incidence of breakthrough infection in this vulnerable population.

The study drew data from an open online registry, EPICOVIDEHA, which collects reports of patients with blood cancers who developed COVID-19 infection. As of August 31, 2021, out of the 4,000 total cases in the registry, there were 113 reported cases of COVID-19 occurring after vaccination. More than three out of four of these breakthrough cases occurred in fully vaccinated people (people who had received one dose of one-dose vaccines such as AstraZeneca, and two doses of two-dose mRNA vaccines such as Moderna or Pfizer). Around 23% had been partially vaccinated, receiving just one dose of an mRNA vaccine, when they became infected with COVID-19.

Within the group of breakthrough cases, 79 patients experienced severe or critical COVID-19 infection, with 75 needing to be hospitalized. After a follow up of 30 days post-COVID-19 diagnosis, 14 (12.4%) patients died, and COVID-19 was deemed the cause of death for all but one of those individuals. The study researchers emphasize that although the mortality rate in patients with breakthrough COVID-19 cases was high, it was still much lower than before vaccines were available. Previous studies using the registry’s data reported that during the pre-vaccination period of the pandemic, people with blood cancers and COVID-19 had mortality rates ranging from 30% to 50% (depending on type of underlying blood cancer).

“Before vaccination, if our patients with hematologic malignancies developed COVID-19, they died in a lot of cases,” said study author Livio Pagano, MD, of the Università Cattolica del Sacro Cuore in Italy. “With these preliminary data, we showed that vaccination is not able to completely protect, but surely it has a strong role in reducing the mortality for COVID-19 for people with blood cancers.”

The study also found that the level of COVID-19 vaccine response was associated with the type of underlying blood cancer. People with myeloproliferative disorders (disorders of red blood cells and platelets) were the least likely to develop COVID-19 after vaccination, and people with lymphoproliferative disorders (disorders of lymphocytes, the white blood cells of the immune system) were the most likely. Of the 113 breakthrough COVID-19 cases, 80% occurred in people with lymphoproliferative conditions such as chronic lymphocytic leukemia, non-Hodgkin lymphoma, Hodgkin lymphoma, and multiple myeloma.

“Unfortunately, people with lymphomas are more likely to have suppressed immune systems and to develop infections, and it is no different for COVID-19,” said Dr. Pagano. “In future studies we will look at the efficacy of additional vaccine doses to understand if they can reduce infection in our patients, especially those with lymphoproliferative disorders.”

Notably, the type of COVID-19 vaccine did not affect the risk of breakthrough cases. Approximately 70% of the patients in this study received an mRNA vaccine such as the Moderna or Pfizer vaccine, and the remaining patients received the AstraZeneca vector-based vaccine or the Sinovac inactivated vaccine. There was no significant difference in the prevention of COVID-19 between these two groups.

“The key message is that we must make a great effort to vaccinate as many people as we can,” said Dr. Pagano. “We can’t only vaccinate our patients with hematologic malignancies; it is also important to vaccinate their caregivers so we can form a barrier of protection around them, because their own immunity from the vaccine is not enough.”