80% Covid immunity lost in 6 months in some after Pfizer shot: US study

Covid-19 antibodies produced by the Pfizer vaccine decreased more than 80 per cent in senior nursing home residents and their caregivers six months after receiving their second dose, a US study has found.

The research led by Case Western Reserve University and Brown University in the US studied blood samples of 120 nursing home residents and 92 health care workers.

The researchers particularly looked at humoral immunity — also called antibody-mediated immunity — to measure the body's defences against the SARS-CoV-2 virus, which causes Covid-19.