Indeed, Sayyid Sistani says that it cannot be worn if it becomes a source of fitna or general disapproval. This is certainly a possibility, and maybe even likely, in the West. Thus, wearing a face mask, if done with the intention of not allowing people to see your face, or at least to the extent of hiding the parts that are attractive and being stared at, should suffice – Sayyid Sistani says it must be covered and does not mention the niqab. Yet, remember that this is situational and does not constitute a continuous requirement