Why is the smallpox vaccine administered in a bunch of little pokes?

Why don’t they just inject you with one jab from a hypodermic? I read that it takes 15 “pokes” with a bifurcated needle to administer the smallpox vaccine. It’s like getting 15 shots, it seems to me.

Actually, the experts argue about exactly this question, “How many pricks does it take to vaccinate against smallpox?”

But as to why the smallpox vaccine is given with multiple, very shallow insertions of vaccine into the superficial layers of the skin rather than as a single injection deep into the skin or even deeper into the muscle, it is because the smallpox vaccine is actually a live virus, called vaccinia, that causes an infection in the superficial layers of the skin. Only by having an active infection in the skin (a “take”) does your body develop immunity to both vaccinia and to smallpox virus. Other immunizations either stimulate your immune system without causing an infection or, injected below the skin, cause a systemic (whole body) infection, not a skin infection.

Where did the number fifteen come from?

Some stuff doctors should know, other stuff they should know where to look it up. This falls in the second category.

From Harrison’s Principles of Internal Medicine: “Vaccine is applied to the skin, which is punctured several times by a sterile needle to penetrate the epidermis.”

Why not one intramuscular needle? “Attempts at control of smallpox began once it was noted accidental exposure to smallpox by scratch on the skin resulted in less severe infection”… guess skin application is safer.

But not without problems of its own. Even skin application can cause vaccinia gangrenosum (local destruction of skin and tissue in immunosuppressed patients, usually fatal); eczema with bacterial superinfection, sometimes fatal; satellite lesions around the inoculation site and encephalitis (swollen brain). Using the skin might also make it easier to test for antibodies in lesser developed countries.

Hope that helped a bit.

The fact that the skin infection caused by the vaccinia virus leaves a characteristic scar is simplified the smallpox eradication program because it enabled the vaccinators to see who was already vaccinated and who wasn’t.

Here are the vaccination method recommendations of the (American) Advisory Committee on Immunization Practices (released this Wednesday) and found at :http://www.cdc.gov/mmwr/preview/mmwrhtml/m2d226.htm

Vaccination Method
The skin over the insertion of the deltoid muscle or the posterior aspect of the arm over the triceps muscle is the preferred site for smallpox vaccination. Skin preparation for vaccination is not required unless the area is grossly contaminated, in which case soap and water should be used to clean the site. If alcohol or another chemical antiseptic is used, the skin must be allowed to dry thoroughly to prevent inactivation of the vaccine virus by the antiseptic. The multiple-puncture technique uses a presterilized bifurcated needle that is inserted vertically into the vaccine vial, causing a small droplet of vaccine (approximately 0.0025 mL) to adhere between the prongs of the needle. The droplet contains the recommended dosage of vaccine, and its presence within the prongs of the bifurcated needle should be confirmed visually. Holding the bifurcated needle perpendicular to the skin, punctures are made rapidly, with strokes vigorous enough to allow a trace of blood to appear after 15–20 seconds (4). According to the product labeling, 2–3 punctures are recommended for primary vaccination and 15 punctures for revaccination. If no trace of blood is visible after vaccination, an additional three insertions should be made by using the same bifurcated needle without reinserting the needle into the vaccine vial. If no evidence of vaccine take is apparent after 7 days, the person can be vaccinated again. Any remaining vaccine should be wiped off the skin with dry sterile gauze and the gauze disposed of in a biohazard waste container.

[slight related hijack] My husband has the option to get vacinated at work, because he is emergency personal. They told his that he could not scratch the scab, or touch the scab then touch his eye. I can understand this. But, they also told him no one can physically touch him for a week. I’ve never heard this before in my life. It sounds wrong to me.Does that mean any health care workers who get vacinated get a week off? If any one has heard of this or knows the reason why, please let me know.[/slight related hijack]

It’s because the vaccine actually causes a disease.

It’s a live virus. You’re getting a small illness to prevent a big illness. Because it’s a live virus, the condition (being infected with the vaccinia virus) is contagious. Just as touching the scab then touching his eye can cause your husband to infect his eye, touching others (or others touching him) can also cause transmission of the infection.

Vaccination information materials caution that those who are vaccinated should avoid all contact with organ transplant recipients, cancer patients, HIV+ people, anyone with either eczema or even a history of eczema, and anyone with an impaired immune system because if the vaccination virus is transmitted to thiem it could kill these patients. This poses a problem for medical workers who are, of course, exposed to such people as part of their job.

Thanks for the replies, everyone. I did Google first to find the answer, but only found sites describing how to vaccinate, not why vaccination is only done just under the skin. That’s where I got the “15 pokes” data.

Hey, I have a smallpox scar from when I was done as a kid. Am I still immune?


The vaccination is only good 7-10 years, typically. On the other hand, being vaccinated at all during a lifetime makes you much less likely to die of smallpox should you happen to get it, and also makes re-vaccination less of an ordeal.