Research of more than 150 patients found the jab stimulated an antibody response in just 39 per cent of people with solid cancers, such as in the breast or prostate, after three weeks.
The single dose was even less effective in patients with blood and bone marrow cancers, with just 13 per cent developing the virus-fighting proteins, compared to 97 per cent of healthy people.
The study found that when patients were given the second dose by 21 days, the percentage who developed detectable levels of antibodies rose to 95 per cent.
Cancer charities and scientists at King’s College London, who led the research, are now ‘urgently’ calling for Britain’s 2million cancer patients to get their second injection sooner.
Under the current UK dosing regimen, Britons are being offered their second dose after 12 weeks on the advice of the Government’s expert advisory group on vaccines.
A decision to delay the second injection from three to 12 weeks was made in January in the face of the highly-infectious Kent variant to bring the epidemic under control quickly.
Cancer patients are among the most vulnerable to dying from Covid and reliant on a vaccine because their body is already weak from battling tumours. They are normally on immunosuppressant drugs which make it even more difficult for their bodies to naturally defend against the virus.
The study did not look at Oxford University’s vaccine, but research has shown both of Britain’s approved jabs have similar success rates.
More than half of cancer patients are not protected against coronavirus after a single dose of the Pfizer vaccine, an alarming study has found (file)
Professor Adrian Hayday, an immunologist at King’s, said: ‘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.’
Dr Simon Vincent, director of research, support and influencing at Breast Cancer Now, described the study as ‘worrying’ and called on an urgent rethink to the vaccine programme.
He added: ‘Worryingly, this study suggests that people affected by cancer, including breast cancer, get little protection against the virus when they only receive a single dose of the Pfizer Covid vaccine, and then do not receive their vaccine boost in the following three weeks.
‘In contrast, the study identifies that when patients received a second dose of the vaccine within three weeks, they had significantly improved immune response and protection against coronavirus.
‘In light of these findings 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 vaccine within a three week timeframe to minimize their risk of both contracting and becoming seriously ill with coronavirus.’
The KCL study, which has not yet been published in a scientific journal, looked at 151 cancer patients and 54 healthy controls. It was done in collaboration with the Francis Crick Institute in London.
Of the cancer patients, 47 received two doses 21 days apart. Researchers found 95 per cent of those with solid cancers developed antibodies after getting the second dose within the three-week time frame.
The researchers said there was also a ‘noticeable improvement’ in blood cancer patients, but the sample size was too small to give an exact percentage.
Participants were given their jabs at Guy’s and St Thomas’ NHS Foundation Trust, King’s College Hospital and Princess Royal University Hospital in Bromley.
Those who did not get a vaccine boost at three weeks did not see any real improvement after a follow-up at five weeks.
Only 43 per cent of solid cancer patients and 8 per cent of blood cancer patients developing antibodies to the Pfizer vaccine at five weeks compared to 100 per cent of healthy controls.
The trial will continue to follow cancer patients post vaccination for up to six months.
While antibodies are not the only part of the immune response that defends against Covid – white blood cells and other, non-Covid specific antibodies are also recruited – having no detectable levels strongly suggests a person is not immune.
Dr Sheeba Irshad, a senior clinical lecturer from King’s College London who co-led the study, 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.
‘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.’