The WHO also raises questions about the validity of results from some of the tests on the market, which it says are not sufficiently sensitive or accurate.
False positives could lead people to think that they are safe from future infection, despite never having had the disease. False negatives would also mean infected people might fail to self-isolate. Advice from the WHO is that immunity certificates may in fact risk continued transmission of the virus, and lead to people ignoring public health advice.
Some experts think enforcing two-tier restrictions on who can and cannot socialize or go to work also raises legal and practical concerns, and that it could have the adverse effect of incentivizing people to seek out infection to avoid being excluded.COVID-19: What are immunity passports and how would they work? | World Economic Forum