I'm not even sure how he came up with that conclusion. The article linked sure doesn't lead to that either. It basically says there is nothing guaranteeing immunity, so therefore a "risk free certificate" or something similar to allow people back to work without restriction cannot be reasonably assumed accurate.
It's basically an argument against opening up economies, really has nothing to do with what he is saying about short term or long term immunity...
These two statements in the link are the crux of their release:
Quote:
Some governments have suggested that the detection of antibodies to the SARS-CoV-2, the virus that causes COVID-19, could serve as the basis for an "immunity passport" or "risk-free certificate" that would enable individuals to travel or to return to work assuming that they are protected against re-infection. There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.
As of 24 April 2020, no study has evaluated whether the presence of antibodies to SARS-CoV-2 confers immunity to subsequent infection by this virus in humans.