Merriam-Webster gives "vaccine" a new definition

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Prefatory note:  In this post, I take the noun "vaccine" as the basic word under discussion, but also consider other cognate terms ("vaccinate", "vaccination").

Here's a standard dictionary entry for "vaccine":


1. any preparation of weakened or killed bacteria or viruses introduced into the body to prevent a disease by stimulating antibodies against it.
2. the virus of cowpox, used in vaccination, obtained from pox vesicles of a cow or person.
3. a software program that helps to protect against computer viruses.

[1800–05; < New Latin (variolae)vaccīnae cowpox = vacc(a) cow + -īnae, feminine pl. of -īnus -ine]

Random House Kernerman Webster's College Dictionary


Let us compare that with the new M-W entry for "vaccine":

: a preparation that is administered (as by injection) to stimulate the body's immune response against a specific infectious disease:

: an antigenic preparation of a typically inactivated or attenuated (see attenuated sense 2) pathogenic agent (such as a bacterium or virus) or one of its components or products (such as a protein or toxin)

: a preparation of genetic material (such as a strand of synthesized messenger RNA) that is used by the cells of the body to produce an antigenic substance (such as a fragment of virus spike protein)

Examples of vaccine in a Sentence

Recent Examples on the Web

//At the time, J&J had been committed to delivering 24 million doses of its vaccine to the U.S. by the end of April.

Melissa Holzberg, Forbes, "FDA Issues Scathing Report Of Baltimore Warehouse Where Johnson & Johnson Vaccines Were Ruined," 21 Apr. 2021

//Pfizer has asked the Food and Drug Administration for emergency use authorization of its vaccine in children ages 12 to 15.

NBC News, "With vaccines open to 16- to 17-year-olds, high schools set up shop to give the shots," 21 Apr. 2021
First Known Use of vaccine

1882, in the meaning defined above

History and Etymology for vaccine

earlier,* "fluid from cowpox pustules used in inoculation," noun use of vaccine "of cowpox" (in the phrases vaccine disease, vaccine matter), borrowed from New Latin vaccina (in variolae vaccinae "cowpox"), going back to Latin, feminine of vaccīnus "of or from a cow," from vacca "cow" (perhaps akin to Sanskrit vaśā "cow") + -īnus -ine entry 1; in extended sense, "preparation of organisms administered to produce immunity," in part borrowed from French vaccin, masculine derivative of vaccine "cowpox, matter from cowpox pustules," borrowed from New Latin or English

*VHM:  emphasis added

From the current M-W entry on "vaccination":

Examples of vaccination in a Sentence

Recent Examples on the Web

//But if the operator demands proof of vaccination or a negative test, the venue can more than double capacity to 35%.

oregonlive, "California’s reopening rules encourage venues to require proof of COVID-19 vaccination," 20 Apr. 2021

//Two of them were within three weeks of full vaccination.

Kristen Jordan Shamus, Detroit Free Press, "Sterling Heights couple among 334 statewide who got COVID-19 after being fully vaccinated," 20 Apr. 2021
Here are some additional etymologies for "vaccine" and "vaccination":

1800, used by British physician Edward Jenner (1749-1823) for the technique he publicized of preventing smallpox by injecting people with the similar but much milder cowpox virus (variolae vaccinae), from vaccine (adj.) "pertaining to cows, from cows" (1798), from Latin vaccinus "from cows," from vacca "cow," a word of uncertain origin. A mild case of cowpox rendered one immune thereafter to smallpox. "The use of the term for diseases other than smallpox is due to Pasteur" [OED].

The earlier 18c. method of smallpox protection in England was by a kind of inoculation called  variolation (from variola, the medical Latin word for "smallpox"). There are two forms of smallpox: a minor one that killed 2% or less of the people who got it, and a virulent form that had about a 30% mortality rate and typically left survivors with severe scarring and often blinded them. Those who got the minor form were noted to be immune thereafter to the worse. Doctors would deliberately infect healthy young patients with a local dose of the minor smallpox, usually resulting in a mild case of it at worst, to render them immune to the more deadly form. Jenner's method was safer, as it involved no smallpox exposure.

(Online Etymology Dictionary)

The terms vaccine and vaccination are derived from Variolae vaccinae (smallpox of the cow), the term devised by Edward Jenner (who both developed the concept of vaccines and created the first vaccine) to denote cowpox. He used the phrase in 1798 for the long title of his Inquiry into the Variolae vaccinae Known as the Cow Pox, in which he described the protective effect of cowpox against smallpox.[12] In 1881, to honor Jenner, Louis Pasteur proposed that the terms should be extended to cover the new protective inoculations then being developed. The science of vaccine development and production is termed vaccinology.


According to Wiktionary, Latin vacca ("cow") — also in Corsican, Dalmatian, Interlingua, Italian (descendant in Alemannic German [Wagge]), Romansch, Sardinian, and Sicilian — is from the Proto-Indo-European *woḱéh₂.  Wiktionary lists dozens of descendants in Romance languages.  (source)

A longer account of the derivation and nature of "vaccine" is given in the American Heritage Student Science Dictionary, 2nd ed.:

A substance that stimulates cells in the immune system to recognize and attack disease-causing agents, especially through the production of antibodies. Most vaccines are given by injection or are swallowed as liquids. Vaccines may contain a weaker form of the disease-causing virus or bacterium or even a DNA fragment or some other component of the agent. See Note at Jenner.

Did You Know? In the 1950s, polio epidemics left thousands of children with permanent physical disabilities. Today, kids are given a polio vaccine to keep them from catching the virus. That vaccine, like most others, works by stimulating the body's immune system to produce antibodies—substances that defend the body against infection by recognizing and destroying disease-causing agents like viruses and bacteria. Scientists usually prepare vaccines by taking a sample of the disease-causing agent and weakening it with heat or chemicals. That way, the agent loses its ability to cause serious illness but is still able to stimulate the body to produce antibodies and provide immunity. But finding safe vaccines that are also effective is a challenge. Today, scientists are able to change the structure of viruses and bacteria at the level of their DNA. They remove the most harmful fragments of DNA and then use what is left in vaccines. New vaccines containing harmless bits of DNA from disease-causing germs have also been developed—all to make diseases like polio a thing of the past.


To refresh our memory, here's the new M-W "b" definition for "vaccine":

a preparation of genetic material (such as a strand of synthesized messenger RNA) that is used by the cells of the body to produce an antigenic substance (such as a fragment of virus spike protein)
Compare the new M-W "b" definition of "vaccine" with this statement from the CDC:

COVID-19 mRNA vaccines give instructions for our cells to make a harmless piece of what is called the “spike protein.” The spike protein is found on the surface of the virus that causes COVID-19.


To determine when the new "b" definition was added to the entry for "vaccine" by M-W, I read through all the screenshots for that entry on Wayback Machine of the Internet Archive beginning from January, 2019.  The first time the new definition ("b") occurs is on January 26, 2021 at 06:51:43.

I wonder if and when other dictionaries will follow suit.


  1. Peter Taylor said,

    April 30, 2021 @ 9:28 am

    Does Webster's have any citation for the computer anti-virus software definition? There isn't one on the linked website, nor any mention of the word "vaccine" in the Wikipedia article about anti-virus software.

  2. Kenny Easwaran said,

    April 30, 2021 @ 11:14 am

    I've never heard anyone use "vaccine" in English to refer to anti-virus software. But several years ago I watched the classic episode of the Pokemon anime that introduce Porygon (which is a computer program Pokemon, rather than a physical creature like most of the others), and it had lots of discussion of a computer virus and a nurse character injecting the computers with vakkushīnu to eliminate the virus. (This episode is also famous for having triggered epileptic seizures in many kids watching it with its flashing lights and colors.)

  3. Charles in Toronto said,

    April 30, 2021 @ 11:14 am

    Interestingly, viral vector vaccines like J&J or AstraZeneca are BOTH a & b. They contain a weak virus that has been modified with genetic material to convince human cells to produce the antigenic substance.

  4. David Marjanović said,

    April 30, 2021 @ 11:35 am

    …but the virus shell is from an adenovirus, not from a coronavirus. It is merely a container that is used to get the coronavirus DNA into the cell.

  5. Cervantes said,

    April 30, 2021 @ 2:25 pm

    Well, the underlying concept is the same — an injected preparation that causes antigens of a pathogen to be presented to the immune system, eliciting a response that protects the subject from future infection by that pathogen. The means of accomplishing this are now more various. A "car" originally meant a wheeled horse-drawn vehicle. Then we had train cars. Now we have automobiles. It's actually still the same basic idea, just accomplished by changing technology.

    Motion pictures are still called "films" and audio recordings are still called "tapes."

  6. Ethan said,

    April 30, 2021 @ 6:52 pm

    It seems to have taken a century for the dictionary to catch up with medical practice. Vaccination against diphtheria using "diphtheria toxoid", a modified version of the toxin produced by the C. diphtheriae bacterium, dates back to the early 1920s. The anti-tetanus vaccine similarly based on modification of the tetanus toxin was introduced a few years later. These are covered by (a) of the new definition but are not caught by the quoted "standard dictionary entry".

    20th century dictionaries may be allowed some leeway because starting in 1948 the most common delivery vehicle for these toxoids was a combined DPT vaccine, which brought in a third component made from inactivated whole-cell B. pertussis. So the standard dictionary entry did apply to the vaccine as delivered, on the basis of the third "P" component.

    Here in the 21st century the anti-pertussis component in the combined vaccine (Tdap or DTaP) is also "acellular" in that it consists of specific selected proteins rather derived from the bacterium. So all three components of the current standard vaccines fall outside that old definition.

  7. Sean Fearnley said,

    April 30, 2021 @ 11:15 pm

    @Kenny Easwaran

    I think you mean 'wakuchin'

  8. Daniel Barkalow said,

    May 1, 2021 @ 1:53 am

    Even in the diphtheria and tetanus cases, the preparation included a less-harmful analogue of the harmful substance that they stimulate antibodies to (although that wasn't a micro-organism). The thing that's really novel with both the viral vector and mRNA vaccines is that they don't contain any of the spike protein or anything similar to it; rather they contain instructions to make spike protein, packaged in something that gets your cells to follow the instructions, thereby causing your own cells to produce what would be a vaccine by definition (a).

    It may also be the case that the viral vector vaccines are incidentally definition (a) vaccines against the vector, but that's an undesired side effect, because the viruses that they deactivate to make the vaccine are pretty unimportant as diseases in humans and having immunity to them may make future vaccines using them as vector less effective.

  9. I've never heard anyone use "vaccine" in English to refer to anti-virus software. said,

    May 1, 2021 @ 7:22 am

    @Kenny Easwaran

    "I've never heard anyone use "vaccine" in English to refer to anti-virus software. "

    I have done so, because I'm a computer guy. I do a fair bit of "How do I stay safe" consulting, I define viruses and malware as infections that have vectors by which they infect the host body, Ward the vector and block the infection.

    The primary vector for viruses is email. I use web based email (Gmail) my mail lives in the cloud, and never actually reaches my PC. I don't run A/V. I warded the vector. (Well, yes, I do run Windows Defender because Windows complains I if don't. But it's low resource, set and forget, and automatically updated. If I *did* disable it, I wouldn't miss it.)

    The primary vector for malware is the browser. I use a browser where security is a design goal. (Firefox, but others are increasingly secure too.) There are add-ons to enhance security, but most strike me as irrelevant. Malware has *never* been a problem here. I warded the vector.

    People I speak to understand the metaphor, as the process of blocking infections by not going to places where you might get infected makes sense to them.

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