England's health service said it expected by Monday that every older resident of care homes would have been offered a Covid-19 vaccination.
British Prime Minister Boris Johnson has called the achievement "a crucial milestone".
Britain, which has one of the world's highest Covid-19 death tolls, is one of the first countries to introduce its vaccine programme.
Mr Johnson's administration is hoping that a successful vaccination programme will restore public faith in his leadership.
He last month said the government hoped to complete the vaccination programme for all care home residents and workers by the end of January.
England's National Health Service said it had offered a Covid-19 shot to people living at more than 10,000 care homes with older residents, while a small remainder have had their visits deferred during a local outbreak.
Mr Johnson said it was "a crucial milestone in our ongoing race to vaccinate the most vulnerable against this deadly disease".
"There will be difficult moments to come and the number of cases and people in hospital remains dangerously high," he said.
"But vaccines are our route out of the pandemic and having protected 8.9 million people with a first dose so far, our roll=out programme will only accelerate from here on."
The government has promised to immunise the most vulnerable people against Covid-19 by mid-February and to offer a shot to every adult by autumn.
So far given 8.98 million people have been given their first dose.
