COVID-19 vaccine equity"

In the letter, Harry - who has previously undergone public testing for HIV - says: "It is striking to now see the world's leading AIDS activists are also leading the call for COVID-19 vaccine equity.

"Vaccinating the world is a test of our moral character and we are experiencing a spectacular failure when it comes to global vaccine equity. Similar to the AIDS crisis, we've yet again revealed over the past year, that the value of life depends on whether you were born and/or live in a rich nation, or a developing country."

In his letter, Harry paid tribute to people who have lost their lives to AIDS.

The prince also referenced Princess Diana's efforts to break the stigma surrounding AIDS and HIV in the 80s and 90s.

Harry - who now lives in the US with his wife and their two children -

wrote: "We honour those whose lives have been cut short and reaffirm our commitment to a scientific community that has worked tirelessly against this disease.

"My mother would be deeply grateful for everything you stand for and have accomplished. We all share that gratitude, so thank you."

Earlier this year, Harry blamed "mass-scale misinformation" for COVID-19 vaccine hesitancy.

The royal - who has Archie, two, and Lilibet, five months, with the Duchess of Sussex - explained: "Until every community can access the vaccine and until every community is connected to trustworthy information about the vaccine, then we are all at risk."