The threat or hazard is SARS-CoV-2, however different jobs may have different activities and possibly multiple exposures, and thus have different risk profiles for each hazard. Therefore, the risk assessment must assess each activity and exposure as it may have a multiplicative or additive effect on the health of workers.
In addition, some tasks may involve more touching of surfaces and may increase breathing rates putting workers at additional risk.
Please note that no control measure reduces risk 100%, therefore when determining which control measure to implement it is important to weigh the advantages and disadvantages, maintenance and technical data sheets. https://www.nioh.ac.za/covid19-guidelines/