I am sorry to hear this I was interested to listen to your talk to learn & understand another perspective from my own. I am a Christian and a doctor. I take my understanding of biology deeply for granted. Multiple myleoma causes a severe immunocompromised state & most people with MM won’t mount an immune response to vaccinations taken while they have MM. It is no surprise the covid vaccination failed in this man’s case. Many of the vaccinated who get more severe covid infections are immunocompromised and a third vaccine dose may help them achieve a little more immunity, but not always enough. Those who are healthy with robust immune systems will mount a protective immune response to lessen the severity of a covid infection if they are to contact covid. I pray that God can heal your anger & your grief & my heart hurts for the loss of your older brother. I pray he believed in God & Jesus & that he is in peace in Heaven.