Is there a difference between “inoculation” and “vaccination”?

Fluzone vaccine
Fluzone vaccine; image Wikimedia Commons/CDC

In a recent family Zoom call, my mum (who’s now in her 80s) made an interesting observation: the main topic of conversation these days – because let’s face it, what else is there to talk about? – is vaccines and vaccinations; but back in the day, when my sibs and I were infants and littlies, the talk was more of inoculations. I still have my old “inoculation” booklets for myself and for my own children when we were babes in arms or toddlers; these were the jabs to prevent diseases like Diptheria and Tetanus, Measles, Mumps and Rubella (“MMR”) that we all had to get before going to school and taking part in the big party called life. But then there’s my yellow “vaccination” booklet, which first started getting stamped with names like cholera and smallpox and yellow fever back in the late ’60s when my family started to travel and live abroad. Do those two words – inoculation and vaccination – have essentially different meanings? Is it to do with what exactly is being injected or ingested, or perhaps to do with their respective goals or the way they are being delivered? Or are they in fact synonymous, with vaccination simply being more trendy in our pandemic-torn times?

Let’s look first at the word inoculation. In its broadest sense it means to introduce a microbe into a system; slightly more specifically it refers to any transfer of tiny amounts of a material to a living organism. When we have a blood test, or even a COVID test, for example, an inoculation is taking place: a culture is inoculated with our body fluids (from our blood or from a nasal swab) to test for the presence of a bacteria or virus. Then there’s the inoculation we’re all more familiar with: an injection (or ingestion) of biological material with the aim of providing or prolonging immunity to certain diseases. So inoculation can refer (and it often does, in popular everyday speech) to an immunization procedure, such as a vaccination, but it doesn’t necessarily or always mean that…

The word’s history is curious – and I think a little back to front. It started off quite specifically, soon after the turn of the 18th century, having just the immunization sense, referring to the intentional introduction of one specific virus – smallpox – “in order to induce a mild and local attack of the disease, and render the subject immune from future contagion”. It wasn’t until almost a century later that it came to refer more widely to the prevention of other infectious or contagious diseases (thanks to Louis Pasteur, as explained below). And it’s only relatively recently that it now also applies to the introduction – accidentally or otherwise – of a virus or germs of any disease into the body through a wound, as well as the deliberate introduction of cells or organisms into a culture medium to see what does or doesn’t thrive and grow.

Now it’s probably becoming clear what vaccination means. It’s a particular form of inoculation, where someone is inoculated with a vaccine specifically in order to induce or increase their immunity. We can thank the British physician Edward Jenner (1749-1823) for both pioneering the vaccination itself and for giving it its name. Jenner, a family doctor from Gloucestershire, noticed that local milkmaids never seemed to show the scars of the dreaded smallpox, with their invariably clear and unmarked complexions. Seeking an explanation, he discovered that the milkmaids had all contracted cowpox through their work, and this was what had apparently protected them from the more terrible disease ravaging the land at that time. Jenner experimented on his gardener’s young son by injecting him with the puss of a cowpox-afflicted milkmaid, and Jenner was thrilled (as I’m sure little James Phipps was too) to see that a subsequent injection of the more lethal pox failed to infect the inoculated child. And so the vaccination was born – but at this stage only for the smallpox virus. As for the name itself: Variolae vaccinae was the name Jenner had given to the milder version of smallpox suffered by cows (and milkmaids), and it derived from the adjective vaccine, “pertaining to cows’, or “from cows”, from the Latin vaccinus (“from cows”). [The Latin word vacca (“cow”) is of uncertain origin, so we’ll never know why the French moo-ers are called “vaches”, the Dutch “koes” or the Danish “kos”.] It wasn’t until almost 90 years after Jenner’s auspicious experiment that the French microbiologist Louis Pasteur developed another vaccine – the first vaccine against rabies, in fact – which involved inoculating an attenuated and much less dangerous form of the virus to effect immunity. And so to the term inoculation he added the word vaccination to refer to inoculations against different diseases, and eventually inoculation alone took on the general sense of immunization.

As my sister pointed out in our family conversation, the British prime minister, Boris Johnson, doesn’t really need to know the difference between a vaccination and an inoculation, because he uses another word entirely: “jab”. Yes, in Blighty they wonder when and where they’ll get their “jabs”. Just as in the US we think and talk and dream about our hypothetical “shots”. (Not to be confused with the shots that deliver a whole other kind of inoculation …). And kudos to anyone who knows what the Scots call these jabs and shots; please insert your suggestions in the comments section below.

Incidentally, the word inoculation was originally a mid-15th-century horticultural term meaning the “act or practice of grafting buds,” deriving from the Latin verb inoculare, meaning to “implant a bud into a plant” – from inoculus meaning “bud” or originally “eye”. Here are a couple of early citations for inoculation in the pathology sense, courtesy of the OED. First, from 1714: E. Timone in Philos. Trans. Abridged 1713–23:  “An Account of the procuring of the Small Pox by Incision or Inoculation, as it has for some time been practised at Constantinople. And from a letter written by Lady M. W. Montagu in 1722: “Accounts of the Growth and spreading of the Innoculation of the small pox, which is become allmost a General practise, attended with great success.”

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