Katalin Karikó and Drew Weissman have won the Nobel Prize in Medicine for discoveries leading to the messenger RNA vaccines that played the most important role in the scientific battle against the Covid-19 pandemic.

The two laureates shared the 1 million dollar prize for their “contribution to the unprecedented rate of vaccine development during one of the greatest threats to human health in modern times”, the Nobel Assembly in Stockholm said on Monday.

The work by Hungarian scientist Karikó and her US counterpart Weissman led directly to the rapid development of mRNA Covid vaccines by Moderna and BioNTech/Pfizer during 2020. These vaccines prevented millions of deaths and played a major role in stemming the growing tide of coronavirus infections, helping authorities end the range of restrictions on social activity during the pandemic.

Karikó, 68, and Weissman, 64, discussed collaboration after meeting by a laboratory photocopier at the University of Pennsylvania in 1998. Over the following 12 years they formed a productive research partnership, as the pair discovered how mRNA — the biological molecule that translates genetic information into proteins — could be manipulated and delivered to human cells in a stable form. They worked out how to prevent the immune system from destroying mRNA, so that its instructions to make useful proteins could be applied in pharmaceutical and vaccine development. Their most important research paper initially attracted little scientific attention on its publication in 2005, the Nobel committee said, but interest picked up after follow-up studies in 2008 and 2010.

Several biotech companies began to work on vaccines against viral infections — culminating in the successful rush to produce Covid jabs that were approved by regulators in the winter of 2020-21. According to Airfinity, a UK-based health analytics company, 5.5bn doses of mRNA Covid vaccines have been administered worldwide to date, with a total sales value of $ 117bn. The impressive flexibility and speed with which mRNA vaccines could be developed has paved the way for the potential use of the technology to produce vaccines against a wide range of infections including flu and treat some cancers and non-transmissible diseases.

Weissman remains a professor at the University of Pennsylvania. Karikó joined BioNTech as a research vice-president in 2013 and she is a professor at Szeged university in Hungary. Much of Karikó’s academic career in Hungary and the US was a struggle for research funding, security and recognition, said Thomas Perlmann, secretary of the Nobel Assembly. Although Karikó is now an adjunct professor at Penn, she made clear in her Nobel Prize interview on Monday that she was not happy with the way the university treated her 10 years ago. “I was kicked out, forced to retire from Penn,” she said. After Karikó’s struggles, the Nobel Prize marked “a dramatic change in her circumstances” following the success of mRNA vaccines, Perlmann said. Biomedical scientists celebrated news of the award. “Kati Karikó is one of the most inspirational scientists I have met,” said John Tregoning, professor in vaccine immunology at Imperial College London. “The ideas that she and Drew Weismann developed were critical for the success of mRNA vaccines.” The medicine award is the first of this year’s six Nobel Prizes. Laureates in physics, chemistry, literature, peace and economics will be announced in the coming days.