One of President Joe Biden's first moves upon arriving in the Oval Office has been to require international travelers to get a negative COVID-19 test before departing, then quarantine on landing; Britain too is considering tighter measures for arrivals. Both basic protective moves are long overdue. They are also an acknowledgment that carefree trips are still many months away.

In part, that's because the virus is still advancing fast — aided by a new, more transmissible and potentially deadlier variant — and vaccinations are not yet keeping up.

It's also because for all the hopes tied up with vaccine or immunity passports, even fast-moving research is not where we need it to be to rely on these certifications alone. To many, they sound like digital versions of old-school yellow fever booklets stapled to travel documents — a familiar, simple fix. Not quite.

Some version of such passes will become part of our lives for the coming years, for the simple reason that there will not be a return to the status quo ante, certainly not anytime soon. There are valid objections around privacy and the risk of exacerbating inequalities. Fortunately, good technology and sound policy should be able to surmount both. Unequal experiences, as a group of academics noted in the Lancet in October, have rarely been cited as a good reason to bar health care treatments altogether, and sound public health measures should not hurt more people than they have to. Governments have time to focus, for example, on catering to often-marginalized groups first, not last; speeding up access to jabs; and ensuring that initiatives facilitate, rather than limit, access.

On the personal data front, there are already encouraging developments. CommonPass — backed by the World Economic Forum and the Commons Project, a nonprofit which develops technology for public use — is a tool that allows anyone to check whether a traveler meets the requirements of the place or country he or she is arriving at. Critically, it also minimizes personal information used, and stores it only in the user's phone or at the source. That doesn't mean that these laissez-passers are about to get us all moving again.

First, consider vaccine passports, which, at their simplest, register that the user has had the required COVID-19 shots. The first problem here is that there are simply not enough vaccinated people to qualify and make the effort significant.

More worrying, though, we lack a lot of the information required for them to replace quarantines and travel bans. We don't know enough about the efficacy of all vaccines that will be provided at scale — nor do we know exactly how long protection lasts. We also do not have enough information about whether vaccination limits transmission, or eliminates it.

More worrisome, for those of us sitting outside Europe and the U.S., is that we do know that not all shots are viewed the same way, with plenty of geopolitics and opaque data muddying assessments of Russian, Chinese and Indian offerings. Will they all be regarded the same way as Western options at the border, when it comes to that, or, say, at the entrance to the Olympic Games? Should they be? Critical questions, given so much of the world will receive these inoculations.

So what about an alternative that focuses on immunity, by testing for antibodies to COVID-19? With this option, we would focus on whether the holder is immune at a specific point in time, whether that is through past illness or vaccination, with no reason to focus on the specifics of the jab. It's an attractively neutral option.

Criticism here usually revolves around the frequency of testing that would be required and the resulting squeeze on capacity, even if the second could arguably be resolved with time. There's also a less-convincing argument that it creates perverse incentives, encouraging people to get infected on purpose to acquire the necessary antibodies. There is little evidence for that: As with debates around Social Security fraud, the free rider problem tends to be exaggerated.

The bigger issue is that we just do not know enough about the markers that signify protection from COVID-19, for the individual or for others, when it comes to transmission. We also need tests that can be done more easily, outside a laboratory, to identify not just antibodies, but actual immunity. Those two basics remain out of our reach for now.

Clara Ferreira Marques is a Bloomberg Opinion columnist covering commodities and environmental, social and governance issues.