It marked the monarch’s first appearance in public since she paid tribute to fallen troops on Remembrance Sunday last November.
After being treated to fly-by from the Red Arrows, the monarch told crowds: “It is a rather nice day. I’m delighted to be here.”
Her Majesty also cracked jokes with Australian High Commissioner George Brandis QC, after he told her coronavirus travel rules have left many Australians stuck in the UK.
The monarch replied: “There are worse places to be stuck.”
The Queen lent her support to the UK’s coronavirus vaccine roll out in February, appearing on a video call to tackle jab hesitancy.
Her Majesty talked about her experience getting the vaccine, and said: “As far as I could make out it was quite harmless. It was very quick, and I’ve had lots of letters from people who have been very surprised by how easy it was to get the vaccine. And the jab – it didn’t hurt at all.”
Turning her attention to those not taking up the vaccine, she said: “I think the other thing is, that it is obviously difficult for people if they’ve never had a vaccine…
“But they ought to think about other people rather than themselves.”
Rachel Bowie and Roberta Fiorito, hosts of the Royally Obsessed podcast, said the monarch’s vaccine rallying call was a “slap on the wrist.”
Ms Bowie said: “What a massive slap on the wrist by the monarch to everyone.
“She is like ‘can’t you think of anyone else other than yourself?'”
Ms Fiorito added: “Yes, she does not normally get that personal and she said it so quickly.”
Prince William, Catherine, the Duchess of Cambridge and Prince Charles have also been vocal in their support of vaccines.
The Duke and Duchess of Cambridge appeared at Westminster Abbey last week, where they were married in 2011, to praise doctors, nurses, and volunteers who set up a makeshift vaccine centre at the historic cathedral.
On March 23, Charles also noted the UK’s resilience as part of the National Day of Reflection.
He said: “We have all been inspired by the resourcefulness we have witnessed, humbled by the dedication shown by so many, and moved, beyond words, by the sacrifices we have seen.
“We are emerging from this time with a renewed confidence in one another and with a strengthened faith in our society—richly diverse in its many communities and cultures, but united in its commitment to the common good and the welfare of others, particularly those most vulnerable.”