Washington: The American dictionary of reference Merriam-Webster on Monday revealed "vaccine" to be its word of the year for 2021, reflecting both the hopes and deep divisions sparked by vaccination as the world wrestled with year two of the Covid-19 pandemic.

"The word vaccine was about much more than medicine in 2021," the dictionary -- which based its decision on surging interest in the term’s definition -- said in a post on its website.

"For many, the word symbolised a possible return to the lives we led before the pandemic. But it was also at the center of debates about personal choice, political affiliation, professional regulations, school safety, healthcare inequality, and so much more."

Merriam-Webster said the development of messenger RNA (mRNA) vaccines required it to expand its definition of the word "vaccine," because the technology triggers an immune response by telling human cells to create antigens, versus classic vaccines, which inject a neutralized form of a virus or antigens.

The word "vaccine" saw a 601 percent increase in definition lookups over the year, compared to 2020.

But "the prominence of the word vaccine in our lives... becomes even more starkly clear when we compare 2021 to 2019, a period in which lookups for the word increased 1048%," Merriam-Webster said. Vaccines are back in the spotlight once again after the discovery of a new Covid-19 variant, prompting renewed appeals for people in the developed world to get vaccinated or boosted against the virus.