The anti-poverty NGO called for governments to improve wealth distribution and to end the "shameful vaccine apartheid".
The world's 10 richest men doubled their fortune during the pandemic while the income of the 99% of humanity has gone down, according to a report by Oxfam.
The anti-poverty charity typically releases its report into inequality ahead of the World Economic Forum in Davos.
The gathering sees thousands of business and political elites descend on the Swiss ski resort for discussions, panels and networking.
For the second year in a row, the event will be held virtually due to COVID-19.
According to Oxfam, a new billionaire has been minted almost every day since the pandemic erupted in March 2020. The fortunes of the world's 10 richest men — including Elon Musk, Jeff Bezos and Bill Gates — more than doubled to $1.5 trillion (€1.3 trillion), making them six times more wealthy than the world's poorest 3.1 billion people.
The ranks of the super-rich have swelled during the pandemic thanks to ample financial stimulus that pumped up stocks, it explained.
"The pandemic has been a billionaire bonanza," said Oxfam International Executive Director Gabriela Bucher. "When governments did the rescue packages and pumped trillions into the economy and to financial markets in order to support the economy for all, what happened is a lot of it went into the pockets of the billionaires."
Meanwhile, 160 million people are projected to have been pushed into poverty. The charity warned that at least 21,300 lives are lost globally every day to inequality, amounting to one death every four seconds.
It said that an estimated 5.6 million people die every year for lack of access to healthcare in poor countries and that hunger kills over 2.1 million people at a minimum.
Oxfam called for rich countries to waive intellectual property rules on COVID-19 vaccines in an effort to expand their production.
"2021 is defined above all by this shameful vaccine apartheid, a stain on the history of our species," it said.
A one-off 99% tax on the 10 richest men’s pandemic windfalls could earn more than $800 billion (€700.8 billion) and be used to fund that effort and other progressive social spending, the group said.
The money "would be able to pay for vaccines for the whole world, have health systems for everyone," Bucher said. "We would also be able to compensate for the damage of climate change and have policies that address gender-based violence," while still leaving the 10 billionaires $8 billion (€7 billion) richer than they were at the start of the pandemic, she added.
It urged governments to focus policies on boosting equality by pouring more money into healthcare and social spending and by pursuing efforts to put an end to tax havens and corporate tax evasion.