Global demand for Covid-19 vaccination surged over the weekend as a rapidly growing number of people worldwide were reported to have been infected with the Omicron variant of the coronavirus.
As governments rush to boost vaccine supplies for their populations, experts have raised concern that the new, heavily mutated variant - already widely seen as a consequence of vaccine inequity - now risks also becoming a contributor to increasing that disparity.
In the United States, where Omicron cases have been recorded in at least 16 states, officials have reported long lines at vaccination clinics and delays in booking new appointments.
Britain, which has confirmed at least 160 cases of the variant, saw an uptick in vaccination turnout after halving last week the waiting time for adults getting booster shots to just three months and offering second doses to more children.
"Omicron will essentially make rich nations hoard vaccines even more, be even less generous about donations, give boosters to entire populations (and) close borders. How will we vaccinate the world at this rate?" said Dr Madhukar Pai, an epidemiologist at McGill University's School of Population and Global Health in Canada.
As Covid-19 vaccines started being rolled out at the end of 2020, public health experts said at the time that to end the pandemic, 11 billion shots on a two-dose regimen would be needed to inoculate 70 per cent of the global population.
Today, 8.14 billion shots - 74 per cent of the initial 11 billion-dose target - have already been administered, yet only 44 per cent of the world has been fully inoculated, according to Our World in Data.
While more than three-quarters of people in the richest nations have received at least one dose, the figure is just 6.2 per cent for those in the low-income countries, most of which are situated in Africa.
"That puts the entire world at higher risk of new, potentially dangerous variants," said Dr Tom Frieden, former director of the US Centres for Disease Control and Prevention. "Uncontrolled spread gives Covid-19 opportunities to evolve."
In addition to their vaccine shortages, which are set to continue, low-income countries are also facing a host of other complications in getting their people inoculated against Covid-19.
"Vaccine supply (to regions of low vaccine coverage) is unpredictable," said Dr Frieden. "Countries don't know how much vaccine to expect and are often given short notice of shipments."
Take for example exports from India - the world's biggest vaccine manufacturer - to the Covax global vaccine-sharing initiative, which helps supply poorer nations with Covid-19 shots. India abruptly suspended all vaccine exports and donations in April to focus on inoculating its own people first. It initially said it would lift the suspension in October, but that was delayed, and it resumed exports suddenly only at the end of November.
On top of supply unpredictability, most donations "do not include necessary supplies such as syringes and diluent, or cover freight costs", said Dr Frieden.
Some vaccine shipments also come with "a very short shelf life, about to expire in three or two months", Dr Lul Riek, southern Africa coordinator for the Africa Centres for Disease Control and Prevention, told Time magazine.
Right now, scaling up production of the shots is of the utmost urgency for alleviating vaccine inequity, according to Dr Peter Muennig, health policy and management professor at Columbia University's Mailman School of Public Health.
"We need a better coordinated global effort to scale up production - of the vaccines, as well as syringes and needles - in many different countries that have existing capacity. That requires international government investment," said Dr Muennig.
"This has the added benefit of allowing countries to lock down China-style without compromising access and reduces bottlenecks in the global supply chain. A few billion dollars a year to maintain this capacity is all that would have been needed."
Yet, year-long talks have stalled over a broad proposal for intellectual property protections covering Covid-19 technologies - and vaccines, in particular - to be waived so that more of the life-saving shots can be manufactured across the globe.
Experts have warned that if wealthy nations and the rich corporations controlling the world's vaccine supplies and technologies do not urgently act to ensure that the poorest countries get the help they need to raise their vaccination rates, then everyone - populations and economies alike - is set for longer, greater suffering.
As Sir Jeremy Farrar, director of British health research charity Wellcome Trust, wrote on Twitter: "Inequity is what will extend the pandemic… Equitable access (to Covid-19 vaccines) is almost the definition… of enlightened self-interest… It is needed urgently."