The injection of medicine into a muscle or vein does not constitute eating or drinking because the medicine does not enter the body by mouth, the normal way that we eat and drink. It may very reasonably be compared to moisture seeping in through the skin, which does not amount to eating or drinking and which, if it happens, does not break one’s fast. So long as there is no intent, by means of the injection, to seek relief from the hardship of not eating and drinking during the day, then it is lawful.
In sum, taking the covid-19 vaccine while fasting in Ramadan or outside of Ramadan does not invalidate the fast because it is for a legitimate medical purpose, necessary for the individual and society, and by no means a substitute for nourishment. Nor can it be likened to taking medicines by mouth. Muslims should not therefore seek to delay their vaccinations on account of fasting.
Shaykh Mohammad Akram Nadwi