People who have had Covid could be just as vulnerable to new South African variant Nervtag chairman says mutations in virus could dull effectiveness of antibodies people had built up from previous infections People who have already had coronavirus could be equally susceptible to the new South African strain of the virus, the chairman of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) has warned. Professor Peter Horby said mutations in the virus could dull the effectiveness of antibodies people had built up from previous infections, warning on Thursday that the new strain could also make new vaccines "less effective".