Shift workers are up to three times more likely to test positive for the coronavirus than employees with a 9-to-5 job, research suggests.
Working nights has been linked to a host of health conditions, including diabetes, cancer and non-coronavirus infections.
To better understand the risk amid the pandemic, scientists from the University of Manchester analysed more than 280,000 people who were swabbed for the coronavirus in hospital.
Results reveal that those who did irregular night shifts were three times more likely to test positive for the infection.
The effect of shift work was found to be "comparable" to that of being obese, non-white or living in the "most" deprived areas, according to the scientists.
Although it is unclear why this occurs, a person's immune system is regulated by their "body clock", which could become "misaligned" during shift work.
While it may sound alarming, regular hand washing, social distancing and getting vaccinated could mitigate these risks, according to the researchers.
More than a year into the pandemic, coronavirus treatments continue to be "limited", making prevention all the more important, the scientists wrote in the journal Thorax.
Occupation is known to influence some people's infection risk, particularly those in healthcare patient-facing roles.
The effect of different working patterns was less clear, despite coronavirus outbreaks emerging at food-processing factories with overnight staff.
Shift work is said to be increasingly common worldwide, making up 40% of employment in some countries.
As well as throwing off a person's body clock, a night-time rota could also lead to sleep deprivation that discourages a worker from exercising or eating well.
To learn more, the Manchester scientists analysed hundreds of thousands of participants aged 40 to 69 in the UK Biobank study, who were tested for the coronavirus in hospital. It is unclear if they were hospitalised with coronavirus complications.
Overall, the irregular shift workers were 2.4 times more likely to swab positive for the infection than those whose rota consistently fell between 9am and 5pm.
Permanently working shifts was linked to a 2.5 times higher risk.
Daytime shift work, specifically, was associated with double the risk of catching the coronavirus, rising to 2.4 times among employees with a permanent night-time role.
The risk was highest among those who worked "irregular" night shifts, at three times that of employees who never did shifts.
The results remained the same after the scientists accounted for other factors that can influence a person's vulnerability to the coronavirus, such as underlying health and weight.
The scientists questioned whether otherwise healthy staff may catch the coronavirus due to some workers, including medics, care home employees and bus drivers, having to work shifts.
They analysed the participants' "physical proximity to a colleague in the workplace combined with estimated disease exposure".
Regardless of whether the job was essential, non-essential or healthcare-related, shift work was linked to a higher risk of infection.
Watch: The health perils of shift work
Shift work may throw a person's body clock – or "circadian rhythm" – into "misalignment", with research suggesting the sleep hormone melatonin could ward off the coronavirus.
These employees may also endure persistent fatigue, causing them to be less vigilant when it comes to hand-washing and social distancing.
There may also be insufficient time for premises to be disinfected between different workers' shifts, suggested the scientists.
"We do believe it should be possible to substantially mitigate these risks through good hand washing, use of face protection, appropriate spacing and vaccination," said study author Dr Hannah Durrington.
The scientists have stressed their research was observational, and therefore does not prove cause and effect.
Nevertheless, the study "shows quite a strong association" between shift work and catching the coronavirus, according to co-author Dr John Blaikley.
The scientists therefore "advocate that shift work is treated as a modifiable risk factor" via "sensible precautions", like a reduced number of employees per rota.
"It is of paramount importance the health and working conditions for shift workers are improved," added Dr Durrington.
Watch: Shift work ages brain prematurely