A third dose of a COVID-19 vaccine can prompt seroconversion in patients with hematologic malignancies who failed to seroconvert after 2 doses, according to a study published in Cancer.

Less than half of patients in this study seroconverted after 2 doses of a COVID-19 vaccine, but 56% of those patients seroconverted after a third dose. 

Researchers also found evidence to suggest that tixagevimab/cilgavimab (Evusheld) can effectively prevent COVID-19 among patients who fail to seroconvert, as none of the patients who received tixagevimab/cilgavimab developed COVID-19.

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For this study, the researchers analyzed 378 patients with hematologic malignancies who received 3 doses of a COVID-19 vaccine. 

After the first 2 doses, 48% of patients had seroconversion. In a multivariable analysis, factors associated with a greater likelihood of seroconversion included:

  • Receiving the Moderna vaccine (vs Pfizer-BioNTech or Johnson & Johnson)
  • Diagnosis of a myeloid malignancy, multiple myeloma/monoclonal gammopathy of undetermined significance, or lymphomas other than indolent/aggressive B-cell lymphomas
  • Being in remission or under “watch and wait” surveillance (vs active disease).

Treatments associated with a lower likelihood of seroconversion included B-cell-depleting monoclonal antibodies and stem cell transplant.

The researchers also assessed seroconversion after a third vaccination in a group of 85 patients who did not seroconvert after 2 doses. In this group, 56% of patients had seroconversion after a third dose. 

The type of vaccine used did not appear to affect seroconversion after the booster dose. Likewise, the rate of seroconversion after the third dose was similar between patients who were on active anticancer therapy and those who were not (53% vs 58%; P =.82). 

In the entire cohort, 33 patients (8.8%) had a documented case of COVID-19, and there were 3 COVID-19-related deaths (0.8%). None of the patients with seroconversion died from COVID-19.

The researchers also analyzed a subgroup of 25 patients who did not seroconvert after a booster dose but received pre-exposure prophylaxis with tixagevimab/cilgavimab. None of these patients were diagnosed with COVID-19, whereas 3 patients who did not receive prophylaxis developed COVID-19 (P =.007), and 1 died. 

“Although all patients with hematologic malignancies should remain vigilant against COVID-19 infection, our study demonstrated an encouraging high rate of seroconversion after a booster vaccination among patients who did not have detectable anti-COVID-19 antibodies after their initial vaccination course,” the researchers wrote. “Risk assessment using antibody testing can identify persistently seronegative patients at the highest risk of COVID-19-related death and thus can help guide management, including prioritizing pre-exposure prophylaxis.”

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Ollila TA, Masel RH, Reagan JL, et al. Seroconversion and outcomes after initial and booster COVID-19 vaccination in adults with hematologic malignancies. Cancer.  Published online July 11, 2022. doi:10.15326/jcopdf.2020.0180