The reason: “Vax” was used 72 times as much as it was in 2020. 

A contributing factor to its rise—aside from its obvious relation to the COVID vaccine drive—is its versatility, Fiona McPherson, a senior editor of the Oxford English Dictionary, told the New York Times. It can be used colloquially as a noun or a verb, and it is the root of many other phrases such as “vax cards” and “getting vaxxed.”

Runners-up on this year’s list were “vaccinate,” which increased in use 34-fold this year, and “vaccination,” up 18-fold. The report also noted other new terms that have taken over social media, from “inoculati” to “Fauci Ouchie.”

Oxford’s rankings were based on data from September 2020 to September 2021, a period marked by COVID vaccines’ development and availability.

In 2019, Oxford picked “climate emergency” as that year’s top term. But in 2020, it opted against a single word or phrase and instead published a review of how the pandemic had influenced our communication through new words, or neologisms, like “doomscrolling.” The report also mentioned terms like “allyship” and “decolonize,” which reflected the social justice movements like Black Lives Matter that also defined the year.

Another shift in English usage this year was the word “jab,” Oxford pointed out. In the past, it was most often paired with words like “verbal” and “subtle.” But now it has taken on a new meaning, most commonly referring to the sharp sting of a needle. Yet the phrase “get the jab,” to describe an injection, is more commonly used in the U.K. than in the U.S., where “get the shot” is more frequent. 

The origins of the word “vaccine,” from the Latin vacca, or “cow,” stem from an entirely different virus. Between the 1790s and early 1800s, scientist Edward Jenner used pus from cows infected with smallpox to inject into people’s skin and thus protect them from the disease. “Vaccine” was used to denote the actual infectious cowpox. And “vaccinate” and “vaccination,” once used to refer to inoculation against only cowpox, has taken on a more general meaning.

In 1801, “vaccinator” started being used to describe someone who advocates for or performs vaccinations, and in 1804, the preferred term morphed to “vaccinist.” In 1851, “vaccinationist” took over for describing vaccine supporters. 

The word “vax” itself first appeared as a noun in the 1980s and then as a verb at the start of the 21st century.

Vaccines have always been a contentious issue, which has influenced the English language. “Anti-vax,” used in the early 1800s as a short form of “anti-vaccinist,” came before “vax.” It has since taken on a number of different spellings, such as “anti-vaxx,” which arrived in 2000.

Social media has been the site of linguistic transformations, both playful and galvanizing.

The Oxford report mentions that in December of 2020, actor Alan Alda tweeted about a conversation he’d had with Dr. Anthony Fauci in which he coined a new term: “Don’t just take a selfie, take a Vaxxie! #vaxxies”

And in May of this year, Secretary of the Australian Council of Trade Unions Sally McManus took to Twitter with her irritation over the pace of vaccine rollouts: “We don’t have a vaccine rollout, we have a vaccine strollout.”

According to Oxford, vaccination-adjacent phrases are plentiful, but so far “strollout” is the one that has graduated from social media to being a frequently cited term in news sources, with an appearance in The Guardian in July.

More health care and Big Pharma coverage from Fortune:

• Foreign travelers to the U.S. will need to be vaccinated and present a negative COVID test before entering starting Nov. 8
• Florida Gov. DeSantis offers $5,000 bonus to lure anti-vaxx police from out of state
• Who is eligible for a Moderna booster?
• Thera-who? These biotech firms are looking to push what’s possible with blood
• 3 states limit nursing home profits in bid to improve care