Data from the SOAP-02 trial, published in the journal Cancer Cell, examines the level of immune protection following the delayed Pfizer vaccine boost in 159 participants, 128 of whom were cancer patients. Although administering the second dose increased rates of seroconversion (development of antibodies to SARS-CoV-2) in blood cancer patients from <20 per cent following a single dose, 57 per cent of double-vaccinated blood cancer patients still failed to mount an immune response to the SARS-CoV-2 spike.
The data highlight the continued vulnerabilities of blood cancer patients to COVID-19. In the absence of protection typically offered by vaccination, the authors argue that the study shows the importance of continuing public health measures to limit SARS-CoV-2 transmission, and the urgency of the booster programme, particularly at a time of very high transmissions of the delta-variant in the UK.
Solid cancer patients, such as those with breast, urological or skin cancers, also showed poor responses to single-dose vaccination, with just 38 per cent seroconversion rates. However, unlike their blood cancer counterparts, these patients showed strong responses to a second vaccine dose given at either 3 weeks or 12 weeks.
While previous studies have argued that delaying the second jab in healthy controls improved the immune response that developed, this new study shows this was not the case for cancer patients. Because the authors' findings have shown that the response to the first dose of vaccine was poor among patients with solid tumours, delaying the second vaccine dose extends the time period over which cancer patients as a whole remained extremely vulnerable.
The trial is led by a cross-institutional collaboration between King's College London and the Francis Crick Institute, with support from Cancer Research UK.
The SOAP-02 trial assessed 159 individuals at Guy's and St Thomas' NHS Foundation Trust, including 31 controls, 72 solid cancer and 56 number blood cancer patients, and their responses following completion of the 2-dose COVID-19 Pfizer-BioNTech SARS-CoV-2 vaccine schedule.
The study examined the production of antibodies (seroconversion) and their function (virus neutralisation); as well T cell responses following the delayed (12 weeks versus 3 weeks) second dose of the vaccine. Assessment of the rates of patients achieving both seroconversion and good T cell responses highlighted the unfavourable situation of blood cancer patients with only 36 per cent achieving antibody and T cell responses compared to 78 per cent of solid cancer patients and 88 per cent of healthy controls.
The study authors urge these vulnerable groups to be protected by people continuing to wear masks, by their social distancing in crowded areas such as public transport, and by the vaccination of school-age children who might be in contact with blood cancer patients or others at high risk.
Lead author Dr Sheeba Irshad, a senior clinical lecturer from King's College London, said, "COVID-19 vaccines are very effective and safe for a majority of the population, but people with moderate to severe compromise of their immune system are not completely protected after the initial dose or after both doses. And so, masks and other COVID-19 protective measures continue to remain necessary for patients particularly with blood cancers. It is also important for our patients to take up the offer of additional dose/s of COVID-19 vaccine recommended to them as part of the continued primary vaccination series."
Lead author Professor Adrian Hayday from King's College London and The Francis Crick Institute said, "The SARS-CoV-2 vaccines have been an extraordinary success, but not for all. With many cancer patients going about their daily routines remaining largely unprotected, society should continue to mask-up and maintain distance, while scientists investigate ways of make vaccines more effective in cancer patients."
Professor Charles Swanton, chief clinician at Cancer Research UK, said, "This study shows that over half of blood cancer patients are unable to mount an antibody response to SARS CoV2 despite being vaccinated twice, which we know is an important step in preventing severe infection risk.
"These results add to a growing body of evidence confirming the vulnerability of patients with blood cancers during the COVID pandemic despite being vaccinated.
According to the researchers, as the world begins to return to normal, we must not forget vulnerable patients like this, who will need ongoing measures to protect them from the transmission and additional approaches to reduce the risk of severe disease. If not, we could see them being confined to isolation approaches for the foreseeable future.