health and safety, environmental protection or other reasons, should it still be regarded as on-topic?
My view is yes. As someone who has one MSc. in policy economics I can personally attest that health and safety regulation and environmental protection is part of policy economics.
Economics by widely used definition is:
“the science which studies human behaviour as a relationship between ends and scarce means which have alternative uses” (Robbins, 1935, p. 16).
The above is textbook definition of economics, and while we can have a debate on whats the demarcation of science I think it is fair to say that most people will accept the Robinson definition (its prevalence in textbooks should indicate mainstream acceptance).
Using the definition of economics we can have a look at some examples of what is economics and what isn't.
how much does Pfizer vaccine reduce rate of infection?
is not economic question as it does not study human behaviour as a relationship between ends and scarce means which have alternative uses
does vaccine mandate increase social welfare?
Is economic question. Social welfare is one of the many ends our society has, mandates are costly in terms of scarce resources such as political capital, or resources spent on vaccination stuff etc. So this is perfectly good economic question.
For example, lockdowns are primarily studied by economists specializing in economics of public health. This John Hopkins lockdown study was done by economist. Reducing spread of disease is also one of the ends humans strive for and lockdowns are not without cost the resources that go into implementing lockdowns could go elsewhere.
However, asking just if lockdowns reduce transmitting the virus without contrasting the transmission to costs to society just looking at transmitting itself is just epidemiology.
For example, asking whether it is optimal for a country to have the same minimum health regulation for food (e.g. no chlorinated chicken) in every region is valid economic question. This is economic question, why should we waste resources implementing the same regulation in every region given our ends of promoting public health? Its not self evident that every region should have the same food regulation to maximize societal welfare.
Asking why chlorinated chicken is bad for your is not an economic question.