Explained: Why are Covid-19 vaccines administered into the upper arm?
Almost everyone vaccinated for Covid-19 over the last 16 months will remember that he or she received a quick prick in the upper arm. This is because most vaccines, including those for Covid-19, are most effective when administered through the intramuscular route into the upper arm muscle, known as the deltoid, experts say.
Why are vaccines generally administered into muscle?
There are several reasons, but the most important one is that the muscles have a rich blood supply network. This means whenever a vaccine carrying an antigen is injected into it, the muscle releases the antigen, which gets dispersed by the muscular vasculature, or the arrangement of blood vessels in the muscle. The antigen then gets picked up by a type of immune cells called dendritic cells, which function by showing antigens on their surface to other cells of the immune system. The dendritic cells carry the antigen through the lymphatic fluid to the lymph node.
“Through the course of research over the years, we have understood that the lymph nodes have T cells and B cells — the body’s primary protector cells. Once this antigen gets flagged and is given to the T cells and B cells, that is how we start developing an immune response against a particular virus, which in this case could be any of the new viruses like SARS-CoV-2, the virus that causes Covid-19, or the previous viruses which we have been running vaccination programs for,” said Dr Rahul Pandit, director of critical care, Fortis Hospital, Mumbai, and a member of the national Covid-19 task force.
