With vaccines there is a risk of antibody-dependent enhancement (ADE), in which antibodies acquired through past infections or vaccinations behave abnormally, causing the ailment in the patient to become severe.
The people taking it now are likely people who have taken numerous other vaccines in the past. Those previous substances injected into their bodies (or the antibodies from them) might be reacting with the new substances injected and producing the horrible effects some are experiencing.
Key sentence from that article:
The people taking it now are likely people who have taken numerous other vaccines in the past. Those previous substances injected into their bodies (or the antibodies from them) might be reacting with the new substances injected and producing the horrible effects some are experiencing.