The U.K. has become the first western country to begin a mass vaccination program against the novel coronavirus on Tuesday as hospitals around the country take part in “the biggest immunization program in history.”

National Health Service (NHS) staff made their final preparations throughout the weekend for the rollout, which will begin with over 80s, front-line health workers and carers with 50 hospital hubs that have been converted to administer the first wave of vaccinations, and more hospitals to begin vaccinating over the coming weeks and months.

“Despite the huge complexities, hospitals will kickstart the first phase of the largest scale vaccination campaign in our country’s history from Tuesday,” NHS Medical Director Stephen Powis said in a statement. “The NHS has a strong record of delivering large scale vaccination programs – from the flu jab, HPV vaccine and lifesaving MMR jabs – hardworking staff will once again rise to the challenge to protect the most vulnerable people from this awful disease.”

The first patient to receive the vaccine outside of clinical trials was Margaret Keenan, a 90-year-old woman from Northern Ireland who has been self-isolating for most of the year. After receiving the first dose, she said, “I wasn’t nervous at all. I don't know what to say, it's just overwhelming as the first really,” before encouraging others to follow suit as "it's the best thing that's ever happened."