All four studies included in this podcast present preliminary data with modest numbers of patients, and therefore, the findings should be interpreted with these limitations. Likewise, the impact of specific strains and waning antibody levels after COVID-19 vaccination will require further follow-up, since the Delta variant was not the dominant strain in circulation at the time of this research. The first two studies assess the immune responses to vaccination in two specific high-risk populations, namely, patients with lymphoma and multiple myeloma. The last two studies, one from a large European consortium and the other based on nationwide data from Israel, report on the incidence, risk factors and short-term outcomes of COVID-19 breakthrough infection in vaccinated patients with hematologic malignancies.