Employers have a duty to follow government advice in order to meet their responsibilities under the HSE Act:- https://www.hse.gov.uk/workers/employers.htm
Firstly, they need to determine what work actually needs to be performed onsite (i.e. that which is “essential”). This will constitute what percentage of work is to be rotated “on-site”.
Secondly, they need to look at individual risk. The following grouping can help:-
Group A: These are people with no underlying conditions, under 70 and have no dependants who are at risk. As healthy children are low risk, this includes some people with healthy families. These people are most likely to recover easily from any illness and should be in the first wave of any infection and can be on a rota.
Group B: These people have no underlying conditions and are under 70 but hay have dependants which are at risk. For example, they live with people who have asthma or conditions who would benefit from a delayed infection. This group would form a second wave of infections and would be on a rota after Group A has been infected/recovered.
Group C: These are people who have an underlying health condition or are over 70. We should try to delay an infection in this population as long as possible so that the NHS is best prepared (e.g. developed a vaccine, have enough ventilators) and should isolate.
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