GENEVA/LONDON (REUTERS, BLOOMBERG) - The head of the World Health Organisation said on Monday (Jan 18) that the world is on the brink of a "catastrophic moral failure" on distributing vaccines, urging countries and manufacturers to share Covid-19 doses more fairly around the world.

"Not only does this me-first approach leave the world's poorest and most vulnerable at risk, it is also self-defeating," WHO Director-General Tedros Adhanom Ghebreyesus said at the opening of the body's annual Executive Board meeting.

"Ultimately these actions will only prolong the pandemic," he added.

Global gaps in access to Covid-19 vaccines are raising concerns that the continued spread of the coronavirus will breed more dangerous versions of the pathogen, weakening medical weapons and further crippling economies.

In a race to catch up with emerging coronavirus variants, wealthy countries are already benefiting from potent vaccines. While the United States, Britain and European Union have given citizens about 24 million doses so far - more than half of the shots administered globally - vast numbers of countries have yet to begin their campaigns.

Disparities in immunity pose a threat to both have and have-not states. Giving the coronavirus an opportunity to advance and generate new mutants would have significant economic and public-health consequences, adding to the pain as the death toll surpasses two million.

"We cannot leave parts of the world without access to vaccines because it's just going to come back to us," said Dr Charlie Weller, head of vaccines at health research foundation Wellcome. "That puts everyone around the world at risk."

Countries are relying on effective immunisations to save lives and revive businesses. The World Bank's projection for 4 per cent growth this year depends on widespread deployment of vaccines. Surging Covid cases and a delay to the delivery of inoculations, however, could limit expansion to just 1.6 per cent.

High-income countries have secured 85 per cent of Pfizer-BioNTech's vaccine and all of Moderna's, according to London-based research firm Airfinity.

Much of the world will be counting on British drugmaker AstraZeneca, whose vaccine is cheaper and easier to distribute, along with other manufacturers such as China's Sinovac Biotech.

Of 42 countries rolling out coronavirus vaccines as at Jan 8, 36 were high-income countries and the rest were middle-income, according to World Health Organisation director-general Tedros Adhanom Ghebreyesus.

A growing number of countries are pursuing their own supply deals, in addition to participating in a global collaboration known as Covax.

Urgency is increasing as the pandemic extends into a second year. New variants that surfaced in the UK, South Africa and Brazil appear to spread significantly faster than earlier versions. Just in the past month, a "new dimension of risk has opened up for the world", said Dr Rajeev Venkayya, president of Takeda Pharmaceutical's vaccines business.

Reducing deaths and illnesses has been seen as the main driver of delivering vaccines rapidly, said Dr Venkayya, who worked in the George W. Bush administration to develop a US pandemic flu plan and directed vaccine delivery for the Gates Foundation.

"We now understand it's also very, very important to control transmission, not just to protect those most vulnerable populations, but also to reduce the evolutionary risk associated with this virus," he said.

While there is no evidence to suggest that the current crop of vaccines are ineffective against those variants, future mutants may be less responsive, Wellcome's Dr Weller said.

Drugmakers say they could tweak their shots to counter new variants within weeks if needed. The likelihood that such adaptations will be necessary has increased, Dr Venkayya said.

Said anti-poverty group Oxfam's health policy adviser Anna Marriott: "The longer the virus is allowed to continue in different parts of the world where we don't have a vaccine, the greater the danger of new variants that could be more aggressive, more virulent or transmissible."

Coronavirus shots have been tested for their ability to prevent symptoms, not transmission. Still, their performance in clinical trials gives an indication of how effective they might be against spread.

The roll-out of shots from Pfizer-BioNTech and Moderna that achieved efficacy levels of about 95 per cent has raised questions about whether everyone will have access to such high levels of protection.

"The gap isn't just about access to vaccines," said Dr Yanzhong Huang, senior fellow for global health at the Council on Foreign Relations. "It's also about access to effective vaccines."

One of the shots that lower- and middle-income countries are relying on, from AstraZeneca and the University of Oxford, sparked worries in Australia that it may not be effective enough to generate herd immunity. Health authorities there, however, said they believe it will be comparable to the Pfizer-BioNTech and Moderna shots in preventing people from getting seriously ill.

The vaccine developed by the UK partners, introduced in the country earlier this month, delivered an average efficacy rate of 70 per cent. That appeared to climb to 80 per cent with a longer gap between doses, based on limited data available, according to regulators.

Lengthening that period to as many as three months from one allows more people to get protected faster, while data shows that the level of antibodies also increases, an AstraZeneca spokesman said.

"An optimised regimen which allows the vaccination of many more people upfront, together with a robust supply chain, means we can have a real impact on the pandemic," he said.

Four vastly differing protection rates have been released on Sinovac's shot, ranging from about 50 per cent to more than 90 per cent. The Chinese developer said the lower number seen in a trial in Brazil is due to participants being medical workers facing a high risk of contracting Covid-19.

"Despite the difference in efficacy rate, they all point to the vaccine's ability for protection, especially against mid- and severe disease," Sinovac said.

While the picture is still coming into focus, cleared vaccines are likely to be similarly effective in preventing serious sickness and death, said Takeda's Dr Venkayya. Where they could diverge is on side effects, the duration of protection and impact on transmission, an even more critical factor in the light of new variants, he said.

Even shots with a lower efficacy level could have a considerable impact. US regulators set a 50 per cent threshold for deeming a candidate effective. But they would require a higher percentage of people willing to get vaccinated to achieve herd immunity, Dr Huang said.

If less-effective vaccines are distributed to emerging markets, it could have significant economic implications, too, and "sharpen differences in pandemic outcomes across countries", World Bank senior economist Justin-Damien Guenette wrote in an e-mail.

Many countries are depending on Covax, which aims to deploy vaccines equitably to every corner of the planet. Yet not all lower- and middle-income nations are waiting for a lifeline. Countries such as South Africa and Malaysia are also pursuing their own supply deals through direct talks with manufacturers, and some regions are set to receive Pfizer-BioNTech's vaccine as well.

"There seem to be indications that countries are losing patience," said Dr Huang of the Council on Foreign Relations.

Covax has secured access to almost two billion doses, with deliveries due to begin in the first quarter, and set a goal of vaccinating up to a fifth of countries' populations by the end of the year. That is far short of the levels of two-thirds or more that many nations are targeting. Some may not get vaccines until 2024, researchers estimate.

The mobilisation is ramping up.

India, a nation of more than 1.3 billion people, kicked off a massive inoculation drive on Saturday, an effort expected to encounter challenges as it extends into rural areas.

Vaccine advocates have called on rich countries to share while pushing companies to scale up manufacturing capacity.

While it is early, the trends are concerning, Dr Venkayya said. "Success is defined as getting vaccines to people everywhere and we're not yet successful in that endeavour," he said.