Bill Gates says the pandemic set world progress on disease back decades in just 25 weeks.
Gates made the claim in a new book which looks at how we can build a practical plan to tackle climate change - even with Covid controlling the way we live, work and socialise.
According to the World Health Organisation, Covid 'substantially hindered' routine immunisation services in at least 68 countries in 2020.
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The disruption could affect 80 million children under the age of one, who are at risk of diphtheria, measles and polio.
Gates, 65, writes: "Globally, Covid-19 has undone decades of progress on poverty and disease.
"As governments moved to deal with the pandemic, they had to pull people and money away from other priorities, including vaccination programmes.
"A study by the Institute for Health Metrics and Evaluation found that in 2020, vaccination rates dropped to levels last seen in the 1990s.
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"We lost 25 years of progress in about 25 weeks."
The business magnate writes that rich nations will now need to invest even more in strengthening world healthcare to be better prepared for another pandemic.
Along with several vaccination campaigns being cancelled in 2020 - Covid has also dented global immunisation efforts by causing fear of travelling to appointments, interrupting transport and bringing in the need for restriction of movement.
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WHO Director-General, Dr Tedros Adhanom Ghebreyesus, said: "Vaccines are one of the most powerful tools in the history of public health, and more children are now being immunised than ever before.
"But the pandemic has put those gains at risk. The avoidable suffering and death caused by children missing out on routine immunisations could be far greater than Covid-19 itself. But it doesn't have to be that way.
"Vaccines can be delivered safely even during the pandemic, and we are calling on countries to ensure these essential life-saving programmes continue."
In Gates' book, How To Avoid A Climate Disaster, he proposes that world leaders should work on projects that simultaneously boost Covid-hit economies and fight climate change.
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Gates states by investing in clean energy development, governments can create jobs quickly and help reduce emissions.
Gates writes: "The year 2020 was a huge and tragic setback. But I am optimistic that we will get Covid-19 under control in 2021.
"And I'm more optimistic that we'll make real progress on climate change - because the world is more committed to solving this problem than it has ever been."
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How To Avoid A Climate Disaster - The Solutions We Have And The Breakthroughs We Need is available from 16 February 2021.
Topics: World News, bill gates