The EU's campaign to vaccinate Europeans against COVID-19 has got off to an uneven start in what will be a marathon effort to administer shots to enough of the bloc's 450 million people to defeat the viral pandemic.

In one mishap, eight workers at a care home in Stralsund, on the north German coast, were injected with five times the recommended dose of the vaccine developed by Pfizer and BioNTech. Four were hospitalized.

"I deeply regret the incident. This individual case is due to individual errors. I hope that all those affected do not experience any serious side effects," district chief Stefan Kerth said on Monday.