Britain's Prince Harry and his wife Meghan on Thursday asked fans to donate money for Covid-19 vaccines as a way of celebrating the second birthday of their son Archie.

"We have been deeply touched over the past two years to feel the warmth and support for our family in honor of Archie's birthday," said the couple, who now live in California after renouncing their royal duties.

In a letter posted on the website of their Archewell non-profit foundation, they praised supporters for their charity donations on Archie's birthday.

"Many of you donate to charities on his behalf, and mark the occasion by giving back or doing an act of service - all through the goodness of your hearts. You raise funds for those who need it most, and continue to do so organically and selflessly. We remain incredibly grateful."

"This year, our world continues to be on the path to recovery from Covid-19. Yet too many families are still struggling with the impact of this pandemic," they said, asking for donations for the purchase of vaccines for "families in the world's most vulnerable places."

"We will not be able to truly recover until everyone, everywhere, has equal access to the vaccine," said the couple, who co-hosted a concert to raise funds for vaccines that is due to air on Sunday.

Along with US President Joe Biden and First Lady Jill Biden, Vice President Kamala Harris will also appear at "Vax Live: The Concert To Reunite The World" where performers will include Jennifer Lopez, Eddie Vedder, J Balvin and HER.

Put on by Global Citizen, an international advocacy organization, the campaign is pushing businesses to "donate dollars for doses," and for G7 governments to share excess vaccines.

It also urges pharmaceutical companies "including Moderna to make vaccines available at not-for-profit prices."