NHS England data shows 93% of the 11,998 health care workers at East Lancashire Hospitals NHS Trust had received at least one vaccination by the end of December, meaning 838 were unvaccinated at that point.
The figures also show 10,767 workers had received two jabs – 90% of staff – and 7,777 had received a booster dose (65%).
The Government's mandatory vaccination rules mean that NHS staff must receive a first jab by February 3 and be fully vaccinated by April 1 to continue working in frontline roles.
Despite widespread protests and calls to delay the policy, the Department for Health and Social Care says there are no plans to extend the deadline and that ensuring staff are vaccinated is the "right thing to do".
The Royal College of GPs and the Royal College of Nurses have encouraged the take-up of vaccinations among NHS workers but are among those who have expressed concern over the rapidly approaching deadline.
Mandatory jabs could have a significant impact on staff retention and put further pressure on the NHS while marginalising the vaccine hesitant, according to the RCN.
The NHS Confederation, which represents the whole healthcare system, said there were risks as well as benefits to a mandatory approach.
Chief executive Danny Mortimer said: "Most health leaders support the introduction of a mandate as it reflects the positive impact that vaccination will continue to have against coronavirus, but they would have preferred longer to implement the policy, particularly given the intensity of winter.
"While the majority of health and care workers have been vaccinated, even small reductions in staffing numbers can cause disruption.
"No leader wants to see this given the high standards of care they wish to maintain, the significant vacancies that exist across the NHS already, and the care backlogs that have built up during the pandemic."
Across England, 94% of healthcare workers had received at least one vaccination by December 31, meaning more than 85,000 were still unvaccinated at this point.
Nearly three-quarters of staff have received a booster jab nationally.
A Department of Health and Social Care spokesperson said: “Health and social care workers look after the most vulnerable people in society, who could face serious health consequences if exposed to the virus.
"Ensuring staff are vaccinated is the right thing to do to protect patients and those in care.
"The vast majority of NHS staff have had the vaccine which is our best defence against Covid-19.”
The data is limited to health care workers who appear in the NHS electronic staff record who could be matched to the National Immunisation Management System – meaning some bank staff could be included in the figures.