The word "vaccine" comes from the Latin word for cow (vacca), as many people know. Infecting people with cowpox (whose medical name is now vaccinia) cross protected them against smallpox, a piece of folk knowledge exploited by Jenner in 1796, when he introduced the practice of inoculating people with cowpox as a preventative for smallpox, then one of world's most deadly scourges. Originally called vaccine inoculation it was quickly shortened to vaccination, and Pasteur later employed "vaccine" for another preventative prepared from infectious material to protect against disease. The back and forth swaying gait of cows also gives us "vaccilate." But I digress. The origin of the word for vaccine isn't news to most people. But what about the other end of the contraction of vaccine inoculation that gave us vaccination? Less known and a bit more interesting.
Again, most people know that oculus in Latin means or is related to the word for "eye." But inoculation doesn't have to do with eyes, at last not directly. Indirectly, plant buds look like small eyes, and the same word, oculus, was used for these small undeveloped flowers or embryonic shoots. Here's a pic (source: Wikipedia), and you can see the resemblance to an eye, at least in shape.
Inoculare in Latin meant to graft a bud from one plant onto another. According to Katherine Barber it came into English around 1400 with this meaning and was used this way for the next 300 years. Again, its modern use was related to smallpox, and again it was folk knowledge that once you got smallpox and recovered you didn't get it again that gave rise to the common practice of intentionally infecting people by "grafting onto them" the infectious matter from a smallpox pustule. In the 1700s the word used for this was "inoculation" in recognition of the analogy with plant grafting.
Now the irony is vaccinia is more dangerous than smallpox, mainly because no one is exposed to smallpox but vaccinia is now again being used to immmunize US military personnel. For most people vaccinia infection is benign, causing nothing but a superficial pustule followed by a scar and longterm immunity to smallpox. But in some people the vaccinia virus develops into a systemic infection that is life threatening. There are risk factors for this aberrant reaction and one of them is a history of eczema. Recently a toddler with a history of eczema came close to death when he developed generalized vaccinia after his soldier father, also with a history of eczema was infected him with his fresh smallpox vaccination (courtesy the US military).
A more common complication is illustrated by the case of an Alaskan woman developed genital vaccinia after having sexual relations with a recently vaccinated partner.
Contact vaccinia, as in the woman's case, is more common than the more severe eczema vaccinatum or progressive vaccinia. According to the US Department of Defense (DoD) Web site, 61 cases (36 lab-confirmed) of contact vaccinia occurred, mainly to spouses and adult intimate contacts, between Dec 13, 2002, and Apr 12, 2007. The MMWR report said lab-confirmed vulvar vaccinia after sexual contact with vaccinated military members has also been reported in New York and Texas since the DoD resumed its smallpox vaccination program.
This is a weird world. We have to be more afraid of the vaccine than a deadly disease.
Sorry, but it's vacillate, not vaccilate.
I'm skeptical of your etymology for 'vacillate', that it derives from the swaying motion a cow makes. It's appealing, but there is something about the single 'c' in 'vacillate' that divorces it from the double consonant in 'vaccinate'.
May I please ask you to cite your source?