Dr Tedros Adhanom Ghebreyesus appealed again for drug companies to prioritise the UN-backed COVAX initiative designed to share vaccines globally.
The World Health Organization has urged countries with high vaccination rates to fulfil their COVID-19 dose-sharing pledges for those countries at immediate risk.
More than 5.5 billion vaccine doses have been administered globally. Some Western countries are already offering third so-called "booster jabs".
"Vaccine inequity is a solvable problem," said WHO Director-General Dr Tedros Adhanom Ghebreyesus, appealing again for pharmaceutical companies to prioritise the UN-backed initiative known as COVAX, which is designed to share vaccines globally.
"We call on manufacturers to prioritize COVAX and AVAT (African Vaccine Acquisition Trust). We call on countries that have already achieved high coverage levels to swap their near-term vaccine deliveries, with COVAX and AVAT to fulfill their dose-sharing pledges immediately and to facilitate the sharing of technology, know-how and intellectual property to support regional vaccine manufacturing."
"I may sound like a broken record. I don't care. I will continue to call for vaccine equity until we get it," he added, using a phrase he has used before for other issues.
Tedros called last week for a “moratorium” on the use of boosters in healthy populations until the end of the year.
Countries including Israel, France and Germany have already started dispensing third doses to certain people; the UK announced plans on Tuesday to offer boosters to anyone over 50 as well as younger people who might be more vulnerable to COVID-19.
Drugmakers -- including Pfizer-BioNTech and Moderna -- have shown no indications they are eager to switch their current tactics, which involve appealing to rich countries and their regulators to authorise booster shots.
To date, fewer than 4% of Africans have been fully immunised and most of the 5.7 billion vaccine doses administered around the world have been given in just 10 rich countries.
COVAX has missed nearly all its targets and has now resorted to begging rich countries to share their vaccine doses.
The WHO and its partners said they hope to provide Africa with about 30% of the COVID-19 vaccines the continent needs by February, badly missing declared targets.
"WHO's global targets are to support every country, to vaccinate at least 40% of its population by the end of this year and 70% of the world's population by the middle of next year. So far, just two countries in Africa have reached the 40% target, the lowest of any region," Tedros said.
"As I said last week, that's not because African countries don't have the capacity or the experience to rollout vaccines, it's because they have been left behind by the rest of the world."