The new findings, which are soon to be published as a preprint, cast doubt on the current U.K. policy of delaying the second dose of the vaccine.
Delaying the second dose can leave most patients with cancer wholly or partially unprotected, according to the researchers. Moreover, such a delay has implications for transmission of SARS-CoV-2 in the cancer patient’s environs as well as for the evolution of virus variants that could be of concern, the researchers concluded.
The data come from a British study that included 151 patients with cancer and 54 healthy control persons. All participants received the COVID-19 mRNA BNT162b2 vaccine (Pfizer-BioNTech).
This vaccine requires two doses. The first few participants in this study were given the second dose 21 days after they had received the first dose, but then national guidelines changed, and the remaining participants had to wait 12 weeks to receive their second dose.
The researchers reported that, among health controls, the immune efficacy of the first dose was very high (97% efficacious). By contrast, among patients with solid tumors, the immune efficacy of a single dose was strikingly low (39%), and it was even lower in patients with hematologic malignancies (13%).
The second dose of vaccine greatly and rapidly increased the immune efficacy in patients with solid tumors (95% within 2 weeks of receiving the second dose), the researchers added.
Too few patients with hematologic cancers had received the second dose before the study ended for clear conclusions to be drawn. Nevertheless, the available data suggest that 50% of patients with hematologic cancers who had received the booster at day 21 were seropositive at 5 weeks vs. only 8% of those who had not received the booster.
“Our data provide the first real-world evidence of immune efficacy following one dose of the Pfizer vaccine in immunocompromised patient populations [and] clearly show that the poor one-dose efficacy in cancer patients can be rescued with an early booster at day 21,” commented senior author Sheeba Irshad, MD, senior clinical lecturer, King’s College London.
“Based on our findings, we would recommend an urgent review of the vaccine strategy for clinically extremely vulnerable groups. Until then, it is important that cancer patients continue to observe all public health measures in place, such as social distancing and shielding when attending hospitals, even after vaccination,” Dr. Irshad added.
The paper, with first author Leticia Monin-Aldama, PhD, is scheduled to appear on the preprint server medRxiv. It has not undergone peer review. The paper was distributed to journalists, with comments from experts not involved in the study, by the UK Science Media Centre.
These data are “of immediate importance” to patients with cancer, commented Shoba Amarnath, PhD, Newcastle University research fellow, Laboratory of T-cell Regulation, Newcastle University Center for Cancer, Newcastle upon Tyne, England.
“These findings are consistent with our understanding. … We know that the immune system within cancer patients is compromised as compared to healthy controls,” Dr. Amarnath said. “The data in the study support the notion that, in solid cancer patients, a considerable delay in second dose will extend the period when cancer patients are at risk of SARS-CoV-2 infection.”
Although more data are required, “this study does raise the issue of whether patients with cancer, other diseases, or those undergoing therapies that affect the body’s immune response should be fast-tracked for their second vaccine dose,” commented Lawrence Young, PhD, professor of molecular oncology and director of the Warwick Cancer Research Center, University of Warwick, Coventry, England.
Stephen Evans, MSc, professor of pharmacoepidemiology, London School of Hygiene and Tropical Medicine, underlined that the study is “essentially” observational and “inevitable limitations must be taken into account.
“Nevertheless, these results do suggest that the vaccines may well not protect those patients with cancer as well as those without cancer,” Mr. Evans said. He added that it is “important that this population continues to observe all COVID-19–associated measures, such as social distancing and shielding when attending hospitals, even after vaccination.”