Over the course of the coronavirus pandemic, there have been hundreds of deaths among healthcare staff from Covid and many thousands off sick or self-isolating, but many hospital staff say they still don't feel properly protected at work.
They blame a sudden weakening in policy on masks and other personal protective equipment (PPE) early in the pandemic.
And the largest health unions and many professional groups say the new variants of the coronavirus could put staff at even greater risk.
Matt Butler was preparing for a weekend shift last March, aware he would be caring for his first Covid-19 patient.
A consultant in geriatrics, he knew that the disease was taking a terrible toll on the elderly.
So he studied the personal protective equipment (PPE) instructions, issued soon after the crisis started, which said he would have to wear a long-sleeved gown, gloves, eye protection - and a particular kind of mask.
Known as an FFP3, it fits closely over the mouth and nose and has an in-built filter to screen out tiny virus particles called aerosols that can linger in the air.
This level of protection seemed to make sense because research into a related coronavirus, Sars, which claimed nearly 800 lives in Asia in 2003, found that aerosols could spread it.
A special training video from the NHS and Public Health England even demonstrated how to fit the mask properly.
So when Dr Butler went to bed on Friday 13 March, he felt reassured.
But when he arrived at the hospital the next morning, he was shocked to find that the official safety instructions had been mysteriously downgraded overnight.
With no warning, staff on wards across the UK would now be getting lower levels of protection - no longer would Dr Butler and his colleagues be equipped with the FFP3 masks that they'd trained for.
Instead, they were told, surgical masks - which are far thinner and cheaper - were now deemed to be adequate.
"I was very scared and a lot of us were very scared," he says.
For this calm and experienced professional, facing a new virus was part of the job.
But how, he wondered, could FFP3 masks be thought essential one day but not the next? How could the risk from infectious aerosols suddenly vanish?
These were questions that would increasingly unsettle him and his colleagues as the pandemic escalated.
And they would lead to increasingly desperate appeals for better equipment by a leading healthcare organisations, the British Medical Association which represents doctors, the Royal College of Nursing, the College of Paramedics and many others.
As Dr Butler puts it: "We just feel like backs have been turned against us and that we're less important, we're seen as more expendable almost."
Who changed the policy and why?
With growing evidence that the virus can spread through aerosols, and with new variants increasing the risks of infection, many of the most prominent medical unions remain worried about the risks.
A decision last year that might appear to be a bit of ancient bureaucratic history is highly relevant right now and - in the view of some - a matter of life and death.
What Dr Butler didn't know when he turned up for work back in March 2020 was that wheels were turning behind the scenes in Whitehall.
March 2020 was a febrile time, with so much unclear about the virus itself, how to treat its victims and how emergency plans for a flu pandemic should be adapted for the coronavirus instead.
Decision-making involved a complex web of organisations known by a dizzying array of acronyms, and unpicking how things unfolded isn't easy.
One of the most important groups is so obscure that it hasn't published any minutes since 2017.
The Advisory Committee on Dangerous Pathogens (ACDP) assesses how to handle biological hazards from anthrax to Ebola.
Back in January 2020, as details emerged from Wuhan, the committee had added the new coronavirus to a grim list of illnesses defined as a "high consequence infectious disease".
That alarming label carried a host of implications for labs and hospitals around the country.
It meant that ambulances had to go through a three-hour cleaning process between patients, and that everyone dealing with the virus had to wear a certain grade of PPE.
That included the FFP3 masks that Dr Butler and others had been poised to wear.
But on 13 March the advisory committee ruled coronavirus would no longer be defined as "high consequence".
The consequences would be far reaching.
Why did this decision matter?
The exact reasons for the decision have not been made public.
A government statement a few days later said it was a "technical" definition that simply reflected the fact that the death rate from the virus was much less severe than expected - far lower than Ebola, for example, where as many as 50% of infected people die.
In any event, the decision acted like a lubricant to the cogs of government.
The Department for Health and Social Care was said to be "moving towards" a shift from FFP3 masks to surgical ones, and a rapid sequence of events then made that happen:
- Prof Jonathan Van-Tam, the deputy chief medical officer, agreed to consult the ACDP, the group advising on dangerous pathogens
- Its chair told him that his committee was "unanimous" in declassifying the coronavirus as "high consequence"
- That day another key committee - Nervtag (the New and Emerging Respiratory Virus Threats Advisory Group) - was told the government supported changing PPE recommendations
So, in a matter of hours, the key figures were aligned and the way was clear for a new message to go out: FFP3s were no longer required on the wards - as Dr Butler would discover when he reached his hospital the following morning.
Cred: David Shukman
BBC Science Editor