Vax has been chosen as the word of the year by lexicographers at the Oxford English Dictionary (OED).
Words related to vaccines have spiked in frequency in 2021 due to Covid, with double-vaxxed, unvaxxed and anti-vaxxer all seeing a surge in use.
OED senior editor Fiona McPherson says vax was an obvious choice as it has made "the most striking impact".
"It goes back at least to the 1980s, but according to our corpus it was rarely used until this year," she said.
"When you add to that its versatility in forming other words, it became clear that vax was the standout in the crowd."
Vax and vaxx are both accepted spellings but the form with one x is more common.
Oxford English Dictionary definitions for vax:
n. A vaccine or vaccination
v. Treat (someone) with a vaccine to produce immunity against a disease; vaccinate
n. A photograph of oneself taking during or immediately before or after a vaccination, especially one against Covid-19, and typically shared on social media; a vaccination selfie
adj. Opposed to vaccination
n. A person who is opposed to vaccination
adj. Having received two doses of a vaccine
Use of the word pandemic has also increased by more than 57,000% this year.
This year's Oxford-winning word, vax, was first recorded in English in 1799, while its derivatives vaccinate and vaccination both first appear in 1800.
All of these words ultimately come from the Latin word vacca, which means cow. According to the OED, this is due to English physician and scientist Edward Jenner's pioneering work on vaccination against smallpox in the late 1790s and early 1800s.