Survivors of a wide range of cancers are more likely than people in the general population to die from seasonal flu even several years after their cancer diagnosis, according to a new study.
The study also found that cancer survivors are more likely to be admitted to the hospital for flu.
As flu and coronavirus are both epidemic respiratory viruses with broadly similar risk factors, the findings suggest cancer survivors are also likely to be at a higher risk for severe Covid-19 outcomes, researchers suggest.
With more than two million cancer survivors in the UK, the scientists say that their results highlight this group may need to be prioritised for vaccination against both diseases.
In what researchers say is the first large study of its kind looking at this issue, researchers from the London School of Hygiene and Tropical Medicine (LSHTM), analysed medical records from 1990 to 2014 of more than 630,000 people in the UK.
This included more than 100,000 survivors of a range of cancers.
Helena Carreira, one of the lead authors of the study and research fellow at LSHTM, said: “We knew that people with cancer are at high risk of severe outcomes from these epidemic viruses soon after diagnosis, but we found that this increased risk also continues for several years after diagnosis.
“This means that vaccination and other preventative strategies are important considerations for the much broader population of longer-term cancer survivors.”
The study, published in EClinicalMedicine, compared the rates of hospital admission from flu and the likelihood of death – between cancer survivors and the cancer-free population.
It found that the risk of these outcomes was more than nine times higher in survivors from lymphomas, leukaemia, and multiple myeloma, compared to those with no prior cancer.
According to the paper, the increased risk persisted for at least 10 years after cancer diagnosis.
Despite the risks being raised compared to the general population, the absolute risks of developing severe flu were still relatively low, with about one in 1000 survivors of these types of cancer admitted to hospital with flu each year.
Researchers found that survivors from other types of cancer also had more than double the risk of severe flu outcomes for up to five years from diagnosis.
These findings persisted even after accounting for other suspected risk factors such as old age, smoking, socioeconomic status, body mass index and other illnesses.
The researchers also discovered that cancer survivors were more likely to have other diseases associated with increased risk of severe Covid-19 outcomes, such as heart disease, diabetes, respiratory disease and kidney disease.
Current guidance on who should be considered vulnerable to coronavirus is largely based on policies developed for previous epidemic respiratory viruses like flu, researchers say.
In such guidance, cancer survivors with no recent immunosuppressing treatment are not considered high-risk.
However, findings from this new study – combined with other recent UK data showing that cancer survivors had a higher risk of dying from Covid-19 – suggest cancer survivors should be included as a vulnerable group for Covid-19 and flu management policies.
Professor Krishnan Bhaskaran, senior author of the study and professor of statistical epidemiology at LSHTM, said: “These findings have an immediate relevance as we enter the winter period: we have a flu vaccine available, and the likelihood of a Covid-19 vaccine in the near future.
“Understanding how vaccination should be prioritised to protect the most vulnerable will be crucial over the next few months.”
The authors acknowledge limitations of their study, including that it is not certain that risk factors for severe flu will have the same associations with Covid-19, and a lack of data on the cancer treatments that patients received.
The research, funded by the Wellcome Trust and the Royal Society, was part of the Beyond Cancer programme investigating the long-term health of cancer survivors.