More than 60 million people in conflict zones and lawless regions could remain unvaccinated against Covid-19, the head of the Red Cross warned.
A global operation to vaccinate billions of people is due to begin.
But millions of the most vulnerable people may never receive a vaccine.
These include about 26 million refugees and tens of millions of internally displaced people.
One of the vaccines must be stored at minus 70°C, creating unique challenges for isolated communities.
"Producers of vaccines must be aware of the special conditions in which hundreds of millions of people are living, who are not close to any cold-chain supply," Peter Maurer, president of the International Committee of the Red Cross, told The National.
“Since the pandemic, we have focused on the very difficult to reach conflict areas, where we are active.
“Our estimate is there are probably more than 60 million people living in areas outside of recognised government control.
“To have access for vaccines in northern Nigeria, parts of Somalia or rural Afghanistan is difficult.
“We must continue to negotiate there to prepare the ground for vaccines to be delivered.”
Specific requirements of the Pfizer and BioNTech Covid-19 vaccine mean healthcare providers must store it either in dry-ice for shorter periods or in specialised freezers at minus 70°C.
The vaccine has proved to be more than 90 per cent effective in trials and is the leading candidate for viral protection, with several others promising similar efficacy.
Daily distribution in the US requires a carefully choreographed project including 12 trucks, 20 daily flights and specifically designed "pizza box" packaging that will keep vaccines safely stored.
The vaccine developed in the US by Moderna remains stable at a regular freezer temperature of minus 20°C for up to six months. After thawing it can last for 30 days and can be kept at room temperature for up to 12 hours.
Once approved, several distribution operations are planned for other vaccine manufacturers elsewhere in Europe, Russia and China that will have similar demands on cold-chain logistics.
Conflict zones most vulnerable to vaccine shortfall
Geographical challenges, poor infrastructure and active conflicts will make it particularly difficult for aid workers to reach populations of refugees, asylum seekers and stateless people.
In Nigeria, a decade-long conflict between militias and the government has forced more than two million people to flee their homes. According to the UN, seven million in the country are reliant on humanitarian aid for survival.
Meanwhile in Somalia, warring factions have displaced close to three million and a further million have been displaced in Afghanistan.
The World Health Organisation is working with its partners Gavi, the Vaccine Alliance, and the UN children's fund to ensure that the infrastructure and technical support is in place to safely deliver as many doses to conflict areas as possible.
“Our focus is to negotiate with state authorities so underprivileged groups and displaced people have access to vaccines,” said Mr Maurer.
“We cannot have distribution cold chains required for the vaccines in some areas, such as northern Nigeria for example."
Inside conflict zones, poor healthcare centres or a total collapse of services often mean regular vaccination programmes are abandoned. Precarious infrastructure and disputed borders can also make delivery of vaccines extremely difficult and dangerous.
These areas often have limited access to electricity, making the consistent refrigeration required for safe deliver a major issue, particularly in rural areas and warmer climates.
"Some regions never make the headlines and by nature are doubly underprivileged as they never get attention," said Mr Maurer.
"I am worried about the forgotten conflicts in Iraq, Myanmar and Central America, which is very often out of the picture and context.
"Yemen falls into the news and then oblivion. We want to equalise these visibility discrepancies.
"No conflict emerges as more serious than another."
Which vaccines will be delivered?
Many different vaccines are likely to become available in 2021 and the ICRC said it would consider which are available to use on staff and vulnerable populations.
“We are exploring all the vaccines that may be available and will decide which staff who are most at risk before we administer,” said Mr Maurer.
“As a default position we will wait for WHO approval on which vaccines are safe. This is a duty of care that is of critical importance.
“We have not taken a decision yet on which one. We should also be talking about testing and medicine.
“There is no reason why we will not use the vaccine that is locally available and considered safe, if it is available in certain places.
“We will not look for a uniform decision for all our operations around the world.”
Funding gaps create uncertain 2021 for aid organisations
Serious funding shortfalls during the pandemic threaten to derail some of the supporting work planned by aid organisations next year.
The ICRC, which employs about 20,000 people in more than 80 countries has run up a $139 million deficit.
Cutbacks have been restricted to operations in largely peaceful countries and at the organisation’s Geneva headquarters, where 100 staff are expected to lose their jobs.
One of the most publicised service cuts was the closure of a specialist centre in Lebanon to treat people wounded in conflicts in Syria, Iraq and Yemen.
Further spending cuts are planned for 2021, with $94m slashed from food aid and operational budgets in 30 countries.
The ICRC has made an appeal for 2.3 billion Swiss Francs ($2.6bn) for 2021 to support its work for people affected by conflict.
Mr Maurer called for a more united international co-operation to help the most vulnerable communities.
“In this region, it is inevitable that burden sharing is discussed again in the wake of the pandemic,” he said.
“Work is needed by humanitarian organisations, but also by political actors.
“There is a powerful argument to develop that you cannot shield yourself and your economy by only investing in your own country.
“Your economy will be haunted if you do not manage the global pandemic and stabilise the most fragile areas. Pandemics will not stop.
“These are issues that must play out in the dynamics of countries who need to stabilise their own economies but also invest in the global public good, such as fighting the pandemic.
“We hope this will lead to more generous support for humanitarian organisations.”