A hospital in the US has had to concede to an unusual request from patients requiring blood transfusions: that they come from donors who haven’t been vaccinated against covid-19. This has led to delays in treatments that caused one individual to experience a life-threatening reaction.

“These requests were often driven by misinformation about vaccine safety and the blood supply, rather than evidence-based transfusion concerns,” says at Vanderbilt University Medical Center in Nashville, Tennessee. “I think one of the most important broader points is that the community blood supply is already highly regulated and carefully screened, and there is no evidence that requesting unvaccinated blood improves transfusion safety.”

Jacobs and his colleagues analysed blood donations that took place at the Vanderbilt centre between January 2024 and December 2025. They found that 15 patients – or their caregivers – had asked for directed donations, when blood is donated by a chosen person, often a relative, rather than being taken from a blood bank.

Directed donations are only permitted in the UK and Australia under exceptional circumstances, such as if an individual has a rare blood type and a suitable blood-bank donor isn’t available. In the US, the practice is allowed more broadly, but discouraged, with policies varying hugely between centres.

The researchers found that all 15 of the patients had directed donations because they wanted blood from a donor who they knew had not been vaccinated. This was specifically against covid-19, says Jacobs. The vaccination status of anonymised donors is not recorded or conveyed by blood banks.

These requests resulted in treatment delays that put the patients at risk. In the most extreme case, the patient’s level of haemoglobin – the protein that carries oxygen around the body – reached a critical level, which can cause organ injury and failure. Another patient developed anaemia.

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“Directed donation is operationally more complex than using the routine blood supply,” says Jacobs. “It requires additional coordination, collection, processing, tracking and timing.”

Although blood is carefully screened before transfusion, direct donations have also been linked to a higher infection risk. This is because they are often given as a one-off, rather than coming from repeat donors in the community who may be known to blood banks and might be particularly cautious of their infection exposure.

Direct donations spiked during the HIV/AIDS epidemic during the 1980s and early 1990s, but they increased in prominence again when the mRNA covid-19 vaccines became available. These involve injecting part of SARS-CoV-2’s genetic code into someone so their cells produce one of its proteins. Their immune system then reacts and destroys cells with this protein. If the individual later catches SARS-CoV-2, their immune system is triggered to fight it off.

Research has repeatedly shown that these vaccines are safe and highly effective, but and other health issues. Conspiracy theories have even wrongly stated that these vaccines contain a microchip and affect your DNA.

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In 2025, a confirmed that receiving blood donations from people vaccinated against covid-19 is safe. “Requests for unvaccinated blood reflect broader uncertainty about vaccines among a proportion of the public, rather than any recognised transfusion risk,” says at the University of Bristol, UK.

And the issue isn’t just affecting the Vanderbilt centre. The Welsh Blood Service stated last year that . There was also a rejected petition to the UK government to split . But in Oklahoma, legislators have proposed mandating that patients have .

“These requests illustrate how misinformation can create real operational burdens for patients, hospitals and blood providers,” says Jacobs. “At the same time, they underscore the importance of addressing patients’ concerns respectfully and thoughtfully, even when those concerns are not supported by evidence.”

Respiratory viruses may activate the growth of dormant cancer cells that have spread to the lungs from elsewhere in the body. Infections like flu seem to spark an inflammatory response that helps the immune system fight off the microbial invader, but has negative consequences for cancer progression.

Cancer deaths often occur when tumour cells migrate from their original location in the body. It is difficult to detect when this occurs, as these cells can lie dormant – not dividing – for years or even decades at their new site before they form tumours.

What triggers these cells to eventually proliferate is unclear, but prior studies suggest that when cancer cells reach the lungs, may play a role. “But no one had really done the studies to really establish cause and effect,” says at the University of Colorado.

To fill this gap, DeGregori and his colleagues used mice that were genetically engineered to grow tumours in their mammary glands. At around 2 months old, each mouse had mammary gland tumours and fewer than 10 dormant cancer cells in their lungs.

The team then infected half of the mice with the H1N1 strain of the influenza virus, also known as swine flu, making them sick for about two weeks. Nine days post-infection, the number of cancer cells in their lungs had increased 100-fold, but hardly changed in the uninfected mice.

When the researchers repeated the experiment but with the SARS-CoV-2 virus, which causes covid-19, they saw about a 10-fold increase in the number of cancer cells in the lungs of the mice, but still no changes in the uninfected mice.

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The researchers hypothesised that such expansions occurred because viral infections increase levels of an inflammatory molecule called IL-6, which helps the immune system destroy viruses, but can also promote tumour growth.

To validate this idea, they repeated the experiment in mice that were genetically engineered to lack IL-6, and found they had substantially fewer cancer cells in their lungs compared with mice with typical IL-6 levels.

Another experiment revealed that IL-6 seems to reawaken dormant cancer cells that had already migrated to the lungs, rather than increasing the spread of these cells from the breast.

But IL-6 levels subside once infections have been cleared. At this stage, the team found that cancer cells in the mice’s lungs stopped proliferating, but had gained properties – such as changes in gene expression – that have been linked to tumours spreading, says DeGregori.

The findings could have implications for people with undetectable levels of cancerous cells in their lungs when they are thought to be in remission, says at the National Institute of Health in Rome, Italy.

To explore if the findings really might apply to people, the researchers analysed health records from 36,800 women in the US who were diagnosed before the covid-19 pandemic with breast cancer that wasn’t thought to have spread.

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The women with a positive test during the first three years of the outbreak were much more likely to have a diagnosis of secondary lung cancer over this period than those whose swabs came back negative or who weren’t tested at all. But some of the women may have had asymptomatic infections, and so not have sought a test, while others may not have had access to one, which would reduce the validity of this result, says DeGregori.

Further studies in people are needed to verify the research and explore how various respiratory viruses and cancer types interact, says Zeuner. “Individual factors are [also] likely to profoundly affect the link between respiratory infections and cancer relapse,” she says.

While the team only looked at swine flu and SARS-CoV-2, DeGregori expects a range of viruses to act in the same way, as many induce increased levels of IL-6. He also thinks the results support yet another reason to get vaccinated. “If I were a cancer survivor, I would make sure I was vaccinated against the common respiratory viruses like flu, covid, so on,” says DeGregori.