Why are vaccines given in the arm instead of the buttocks? How many "vaccine marks" do you have on your arm?

Expert in this article: Li Xue, Peking Union Medical College, Doctor of Medicine

In order to prevent diseases, we have been vaccinated with various vaccines since birth, such as BCG vaccine, hepatitis B vaccine, polio vaccine, diphtheria, pertussis and tetanus vaccine, meningococcal vaccine, measles, mumps and rubella vaccine, hand, foot and mouth vaccine, varicella vaccine, HPV vaccine, and the new coronavirus vaccine in recent years, etc.

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Some vaccines will leave scars while others will not; some people have “vaccine marks” on their arms while others do not.

What is going on here? Let’s talk about the “vaccine mark”.

How did the “vaccine mark” come about?

There are many types of vaccines:

1

Live vaccines: vaccines made from live viruses or bacteria, such as the earliest smallpox vaccine. Since this type of vaccine is equivalent to a single infection and has a greater reaction, this type of vaccine is now basically non-existent.

2

Attenuated live vaccines: As the name suggests, they use live pathogens with reduced toxicity or very similar low-toxic pathogens. The BCG vaccine for preventing tuberculosis is an attenuated live vaccine.

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3

Inactivated vaccines: use complete, killed (inactivated) or modified pathogens to make them unable to reproduce and thus cause disease, such as the Sinopharm inactivated COVID-19 vaccine used in our country.

4

Recombinant protein vaccine: It is not a complete virus, but is composed of one or several important parts of the virus, such as HPV vaccine.

5

In addition, there are nucleic acid vaccines, polysaccharide vaccines, etc.

The immunogenicity of live viruses/live attenuated viruses is generally stronger than other types of vaccines. After vaccination, the human body's immune response is also stronger, which may leave a "vaccine mark" at the injection site.

For example, BCG will cause an inflammatory reaction about 3 weeks after vaccination. The vaccination site will become red and swollen, and the middle will soften to form a small pustule. The pustule will then burst, and a scab will begin to form 1-2 weeks after the pus is drained. Finally, the scab will fall off to form a round scar, also called a "BCG scar."

What kind of vaccines will leave marks?

Although there are many types of vaccines, there are currently only two types that will leave a "vaccine mark": smallpox vaccine (also called cowpox vaccine) and BCG vaccine.

In May 1980, the World Health Organization announced that the smallpox virus had been eradicated from humans. my country canceled the nationwide cowpox vaccination in March 1981.

Therefore, most people born in the 1980s, 1990s, and 2000s have not been vaccinated with the smallpox vaccine. They usually only have one "vaccine mark" left by the BCG vaccine on their arms, while people born before the 1980s may have two scars on their arms.

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Not everyone who has received the above two vaccines will have a "vaccine mark". There are exceptions to scarring depending on individual constitution. For example, some newborns do not have such a strong immune response after vaccination, so the scars may not be obvious. The scars will gradually fade with age and will basically be invisible in the end.

Why is the vaccine given in the arm?

Most vaccines are given by intramuscular injection, which is injected into the arm. In addition, there are oral vaccines, such as the "sugar pill" vaccine for preventing polio virus, and the measles vaccine, which is injected under the skin.

The arm is the most common vaccination site, which is related to the following factors:

1. The fundamental purpose of the vaccine is to stimulate the body's own immune response, to remember the pathogen, so that it can respond quickly and eliminate it the next time it is encountered.

The human body's lymph nodes are a key part of the immune system. Vaccination close to the lymph nodes is more conducive to activating the immune response. Many vaccines are injected into the deltoid muscle of the arm because the deltoid muscle and the lymph nodes under the armpit are very close.

If the vaccine is given in the thigh, it is not far from the inguinal lymph node collection.

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2. Intramuscular injection can keep the vaccine reaction local. If it is injected into fat tissue, reactions such as redness and swelling may be more severe.

The size of the muscle also affects the choice of injection site. Children under three years old have smaller arm muscle tissue, so intramuscular vaccines are usually given in the thigh close to the inguinal lymph nodes.

3. From the perspective of convenience, injecting the needle on the arm is the most convenient and acceptable.

What should I pay attention to when getting vaccinated?

✔ If you suffer from tuberculosis, nephritis, heart disease, immunodeficiency, etc., you should postpone vaccination, consult your doctor whether you meet the vaccination conditions, and get a booster shot at the appropriate time.

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✔ Children should not eat warm or hot food or drink within half an hour after receiving oral polio vaccine.

✔ Make sure to get enough rest the day before vaccination. Try not to stay up late, drink alcohol, or eat spicy or irritating foods to keep your body in the best condition.

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