Why do we usually get the upper arm vaccinations?

Over the past year and this year, millions of people have rolled up their sleeves to receive the COVID-19 vaccine. But the question arises here and you may have thought about it, why do we receive vaccinations on the upper arm in particular?

Why are vaccinations and the vaccine given in the upper arm?

First of all, it should be noted that most, but not all, vaccines are given into the muscle - this is known as an intramuscular injection.

Some other types of vaccines are given as drops in the mouth, such as the rotavirus vaccine.

Others, such as the measles, mumps, and rubella vaccine, are given just under the skin. However, most types of vaccinations are given into the muscle.

But what is the importance of giving the vaccination into the muscles? Specifically in the deltoid muscle located in the upper arm?

muscle immune cells

Muscles are an ideal site for giving vaccinations because muscle tissue contains important immune cells.

These immune cells recognize the antigen, which is a small piece of virus or bacteria that is introduced into the body through vaccination to trigger an immune response.

In the case of COVID-19 vaccines, it is not the introduction of an antigen but the administration of a scheme to produce the antigens.

Immune cells in muscle tissue pick up these antigens and present them to the lymph nodes. Injecting the vaccine into muscle tissue keeps it localized, allowing immune cells to sound the alarm and tell other immune cells to start working.

Once the vaccination is recognized by immune cells in the muscle, these cells carry the antigen to the lymphatic vessels, which transport the antigen-bearing immune cells to the lymph nodes.

Lymph nodes, which are the main components of our body's immune system, contain more immune cells that recognize the antigens in vaccines and initiate the immune process to produce antibodies.

Clusters of lymph nodes are located in areas close to the sites where the vaccine was given. For example, many vaccines are injected into the deltoid muscle because it is close to the lymph nodes just under the armpit.

Likewise in the groin, when vaccines are given in this area, the lymphatic vessels do not have to travel far to reach the lymph nodes in the groin.

Muscles keep irritation in place
Muscle tissues also tend to keep graft reactions localized. Injecting it into the deltoid muscle may cause local inflammation or soreness at the injection site.

If certain vaccines are injected into adipose tissue, the chance of irritation and an inflammatory reaction increases because adipose tissue has poor blood flow from muscle tissue, resulting in poor absorption of some components of the vaccine.

Vaccines that involve the use of adjuvants — or ingredients that boost the immune response to an antigen — must be administered into the muscles to avoid widespread irritation and inflammation. Adjuvants work in several ways to stimulate a stronger immune response.

Another critical factor at the site of administration of the vaccine is muscle size. Adults and children three years of age and older tend to receive vaccinations in the upper arm in the deltoid muscle.

Younger children receive their vaccinations in the middle of the thigh because their arm muscles are smaller and less developed.

A final thing is that receiving vaccinations in the arm is easier and faster for the health worker and the recipient of the vaccination, especially in the case of vaccinations against epidemics, which means vaccinating the largest possible number of people in a short time.