New research has found that delaying the second dose of the Covid-19 vaccine could leave cancer patients and those who are immunosuppressed vulnerable to the disease.

The study, led by a cross-institutional collaboration between King’s and the Francis Crick Institute, found that people with cancer get little protection against the virus when they only receive a single dose of the Pfizer Covid-19 vaccine, and then do not receive their vaccine boost in the following three weeks.

The data from the study revealed that 21 days after the first dose of the Pfizer vaccine, anti-SARS-CoV-2 antibody responses vaccine were only 39% and 13% in the solid and haematological cancers. This compares to 97% in patients without cancer.

However, when the second dose of the vaccine was administered three weeks after the first dose, the immune response improved significantly, with 95% of solid cancer patients showing detectable antibodies to the SARS-CoV-2 virus within just two weeks.

Contrastingly, those who did not get a vaccine boost at three weeks did not see any real improvement, with only 43% of solid cancer patients and 8% of blood cancer patients developing antibodies to the Pfizer vaccine at five weeks compared to 100% of healthy controls.

Three-month period of poor protection could lead to new Covid-19 mutant strains

The SOAP trial enrolled 151 cancer patients and 54 healthy controls. Of these, 47 received two 30-μg doses of BNT162b2, administered intramuscularly 21 days apart at Guy’s and St Thomas’ NHS Foundation Trust, King’s College Hospital and Princess Royal University Hospital, Bromley. However, in line with changes in national government guidelines, those participants who had not received their second shot by December 29th, 2020, received only one dose within the study period with a planned follow up booster 12-weeks later.

These results have implications not just for cancer patients but for their families, friends and carers too. This is because a three-month period of poor protection can allow the virus to spread to those around the patients and may even create conditions favouring the emergence of new mutant strains.

For this reason, the senior authors of the study, Dr Sheeba Irshad from King’s and Professor Adrian Hayday from King’s and the Francis Crick Institute, are calling for an urgent re-evaluation of the Pfizer vaccine dosage intervals for those who are classed as extremely clinically vulnerable.

Dr Irshad said: “Our data provides the first real-world evidence of immune efficacy following one dose of the Pfizer vaccine in immunocompromised patient populations. We show that following first dose, most solid and haematological cancer patients remained immunologically unprotected up until at least five weeks following primary injection; but this poor one dose efficacy can be rescued with an early booster at day 21.”

Cancer patients to continue to observe all public health measures 

Dr Irshad also highlights that it is therefore very important for cancer patients to continue to observe all public health measures in place such as social distancing and shielding when attending hospitals, even after vaccination.

Professor Adrian Hayday added: “The vaccine is very impressive in its impact on healthy individuals and our study shows that it can clearly bring immense benefit to cancer patients too, but in most cases, this is only after boosting. Cancer patients should be vaccinated and boosted quickly and their responses, particularly those of blood cancer patients, should be intensively monitored so that those who mix with family, friends and carers can be confident of their environment.

"These insights were only gained by way of truly intensive, selfless commitment of many young research fellows working together as a team. In making that commitment we have been brilliantly supported by our host institutions.”

In light of these findings, Dr Simon Vincent, Direct or Research, Support and Influencing at Breast Cancer Now has announced that he is supporting the authors’ demand for a re-evaluation of the dosage interval.

He said: “We are calling on the Joint Committee on Vaccination and Immunisation to urgently review the evidence presented in this study, and to consider adapting its strategy to ensure that people who may benefit from this approach, including those with breast cancer, receive both the first and second dose of the Pfizer Covid-19 vaccine within a three-week timeframe to minimize their risk of both contracting and becoming seriously ill with coronavirus."

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