Let me address several important considerations. For the WHO to advise against travel to Rio for the Olympic Games would have significant implications. It would impact travel to every country impacted by Zika virus with potentially significant economic consequences - often borne disproportionally by the poor. Saying "don't travel to Rio" is saying don't travel to a large part of the world - and for how long? Peter Singer is optimistic that the travel ban on Brazil would be temporary because a vaccine will be found, however in 2002 it was announced that a vaccine for the closely related West Nile Virus was in preparation with licensure anticipated within three years. But there are currently no vaccines licensed for preventing West Nile Virus disease in humans. Despite millions of dollars of development attempts, there is no human vaccine available for SARS virus recognised in 2003 or for the MERS virus first reported in 2012.
There is a guiding ethical maxim of medical practice: "first do no harm". There are always academis and others willing to "sound the alarm" as if there is no down side to scaring people. As an ethicist Peter Singer may be well versed in assessing ethical arguments but he is clearly not schooled in assessing epidemiological risk assessment, risk communication in outbreaks and risk management. Not to say an ethicist cannot inform technical debates outside their field but it probably should be done in support of international expert groups. While Peter Singer claims the "facts are not clear", it is clear that there is not enough evidence to recommend against generic travel to the Rio Olymics - to do so would cause harm and the benefit is extremely uncertain. Adding his voice to this call may well be unethical.
