The move was in response to the high number of deaths in the care sector during the pandemic but was widely criticised, among fears of an "exodus" of care staff.
NHS England data shows 2,167 people were working in older adult care homes across Doncaster on January 2 – the most recent date for which figures are available.
This was 124 fewer than the 2,291 recorded on July 18 – days before a 16-week “grace period” for care workers to get their first jab started.
Across England, the number of staff in older adult care homes dropped by 17,000 over the same period.
It is unclear how many workers left as a result of the mandatory vaccine policy.
The Government announced it is relaxing immigration rules to make up for “severe and increasing difficulties” with recruitment and retention in the care sector.
It follows a recommendation from the Migration Advisory Committee that care jobs be made eligible for the health and care visa, designed to help migrants get work visas to fill jobs where there are shortages.
Care providers are experiencing high vacancy rates and turnover, and pressure on staffing is being exacerbated by the spread of the Omicron variant.
Sam Monaghan, chief executive of MHA, the UK’s largest charitable care provider, said: “Essential care and support for older people is facing a staffing crisis the likes of which we have never seen before.
“The changes to immigration rules are a very welcome step forward in addressing the ongoing care staffing crisis.
“However, it will be some months before older people feel the benefit of these much-needed changes."
Vic Rayner, chief executive of the National Care Forum, said it was "imperative" that all organisations will be able to use the scheme "at speed".
She added: “At present it is complex, and organisations currently using it for wider roles recognise the financial and bureaucratic burdens inherent in the system.”
The NHS data shows 2,098 workers at older adult care homes in Doncaster had received two Covid jabs by January 2 – 97 per cent of staff employed on that date, and up from 1,829 on July 18.
Across England, 95 per cent of older adult care home workers have received two doses of a Covid jab.
The Department for Health and Social Care said new starters can be deployed to work care homes 21 days after receiving one dose of the vaccine and are required to get a second jab within 10 weeks.
Others not fully vaccinated may consist of those on maternity leave, long term sickness or otherwise not currently deployed, a DHSC spokeswoman added.
They said £462.5 million had been provided for recruitment and retention, and the department was working with the care sector to encourage booster uptake.