The Red Cross launched a plan Thursday to help vaccinate 500 million people against Covid-19 in over 100 countries, warning that leaving out the world's poorest could seriously backfire.

The International Federation of Red Cross and Red Crescent Societies said it would throw its weight into the distribution and acceptance of vaccines among some of the hardest-to-reach communities.

The Geneva-based IFRC said it would spend 100 million Swiss francs ($111 million, 92.5 million euros) on the push and was already working with governments in more than 60 countries to see where its help could be the most effective.

"The current lack of equity in the rollout of Covid-19 vaccines is alarming and could backfire to deadly and devastating effect," IFRC secretary general Jagan Chapagain told reporters.

He said nearly 70 percent of vaccine doses administered so far had been in the world's 50 richest countries while only 0.1 percent had been deployed in the poorest 50.

"It could prolong or even worsen this terrible pandemic," Chapagain said, noting that if the virus continued to circulate and mutate in large areas of the globe, even those who have been vaccinated in wealthier countries would not be safe.

He called for richer countries to share vaccines once they had immunised their most vulnerable populations.

Otherwise, "the emergence of variants in far-away low-income countries will shatter the illusion of safety in wealthier countries," said Chapagain.

The IFRC, which calls itself the world's largest humanitarian network, said it will bolster national vaccination efforts, including supporting logistics and countering misinformation about vaccine efficacy.

IFRC health director Emanuele Capobianco it was already supporting vaccination campaigns in Austria, Brazil, Morocco and Kuwait, among other countries.

It is also aiming to reach refugees and undocumented migrants.

On Wednesday, the Covax programme to ensure equitable worldwide access to Covid-19 vaccines published its first distribution list.

Some 145 countries are set to receive an initial 337.2 million doses -- enough to immunise 3.3 percent of their collective population by mid-2021, with first deliveries expected in late February.

For many poorer countries, the scheme will be their only way of accessing vaccines.

"The equitable distribution of Covid-19 vaccines between and within countries is more than a moral imperative: it is the only way to solve the most pressing public health emergency of our time," said Chapagain.