Children's charity UNICEF has warned that millions of doses of COVID-19 vaccines could be wasted if rich countries send large amounts of leftover doses to poorer nations in one go, BBC News reported on Tuesday.

UNICEF stated that there needed to be a steady supply throughout the year because poor countries do not have resources to use them all at once.

Reportedly, the UK and other countries have promised to donate their surplus doses, but they have been asked to give more earlier.

The charity's vaccine lead, Lily Caprani, told BBC Newsnight that countries needed to vaccinate their own populations at the same time as the rest of the world.

"At some point, no doubt, we will need to vaccinate under-18s. But the priority at this moment has to be making sure that all of the vulnerable and priority groups around the world get vaccines," she said, adding, "So we're saying countries like the UK and the G7 need to donate their doses to those low income countries now, while still vaccinating their populations at home."

Caprani called on G7 countries to start donating vaccines now, as well as throughout the summer and the rest of the year.

"Low income countries need a steady supply that they can get off the tarmac and into the arms of health care workers. The unintended consequence of saving all these vaccines up to Christmas time is that countries won't be able to absorb them and roll them out and therefore they could end up going to waste. We could see millions of doses of vaccines not used and expiring, and that will be a tragedy," she said.

However, UK Health Secretary Matt Hancock had said last week that vaccinating children in the UK would take priority over sending doses abroad. Unlike other countries, the UK has not revealed how many doses it plans to donate to the global COVAX vaccine-sharing scheme, saying only that it will donate its excess doses. On 4 June 2021, Hancock reportedly said the UK did not currently have any spare doses.

Celebrities, including Billie Eilish and David Beckham, are backing UNICEF's plea ands have signed a letter to the G7 group of rich countries - including the UK - asking them to donate 20% of their vaccines by August 2021.

In the letter, the celebrities said UNICEF was already delivering vaccines in poor countries, but the charity was 190 million doses short.

According to the letter, the G7 countries - the UK, Canada, France, Germany, Italy, Japan and the US - will soon have enough to donate 20% of their doses between June and August 2021, without significant delay to their own rollouts, and doing that would provide more than 150 million doses to COVAX.