Regardless of the context – professional or domestic, in relation to the state, or in relation to private entities, human rights are inviolable. Indeed, under extreme conditions (e.g., war, natural events), human rights can be restricted under strict conditions. However, no matter how critical the situation is, human rights can never lose their ‘essence’. If every human being has the right to physical integrity, it means that the act of requiring a person to get a COVID-19 vaccine will automatically cancel the fundamental right to physical integrity. Similarly, the act of requiring a person to provide proof of vaccination as a condition for work will lead either to the cancelling of the person’s right to work or to cancelling of the person’s right to physical integrity. If we can imagine a totalitarian society where vaccination would be mandatory for work, we will observe that, in a such society, a human being should choose between the two rights: the right to work or the right to physical integrity. Let us imagine a pyramid of rights! The basis of the pyramid would be, more than likely, the human dignity. Could you contradict me if I say that the dignity is the main source for all human rights? Probably not. But in a sci-fi scenario (e.g., Big Brother, Apocalypse Z…) in which a person would be forced to a medical procedure as a condition to work, would human dignity still have any value? Probably not.
I partially answered the question in the title by saying that vaccination cannot be mandatory because the human rights and mandatory vaccination cannot coexist. Human rights are stipulated in the primary legislation of the States (in the Constitutions or, at EU level, in the EU Charter of Fundamental Rights). If the mandatory vaccination is incompatible with the primary legislation on human rights, it will be, legally speaking, impossible for a secondary law to require employees to get a COVID-19 vaccine as a pre-condition to go to work. The Charter of Fundamental Rights of the EU (‘the Charter’) stipulates, in Article 8, the right to the protection of personal data. The right to data protection is applied horizontally in the relationship between the employee and the employer. The status of the person (vaccinated or unvaccinated) falls under the notion of personal data, and, as a consequence, the employees are forbidden to process this information without the consent of the subject or without another legal basis. In other words, to legally process the vaccinated/unvaccinated status of the employee, the employer will have to comply with the GDPR (e.g., conditions for consent, legal basis, etc.). Since the abolition of slavery, employees are human beings endowed with rights, and dignity is neither at a discount nor negotiable.