Several countries and business sectors are pushing for the quick roll out of digital COVID-19 vaccine passports, as a means to open up the economy and in particular the travel and tourism industry. The question is whether such vaccine passports are actually useful.
To answer this question, let us consider the use of vaccine passports for (inter)national travel, as a necessary requirement to be allowed entry into a certain country or region. The (assumed) goal of vaccine passports here is to control the spread of the virus. Therefore to answer their usefulness, we need to know whether vaccinated people are less likely to be carriers of the virus and transmit. Unfortunately, the jury is still out on whether COVID-19 vaccines prevent its transmission, although initial research shows that it may reduce transmissibility. The higher the reduction of transmission, the more useful COVID-19 vaccine passports become. But as long as the transmission is not guaranteed to be zero, such passports do nothing to fully prevent the spread of news variants of the virus that have developed elsewhere.
Moreover, a vaccine passport is only useful for a limited period of time, and in a limited set of circumstances.
If a country has a high rate of incidence, preventing people from other countries entering is the least of its worries, especially if the other country has a lower incidence rate. So it is only useful to limit travel from other countries with a high incidence rate to a country with a low incidence rate. If the departure country has a high incidence rate, there are relatively few people that are vaccinated (otherwise the incidence should be low), and so there are relatively few people that can apply for a COVID-19 vaccine passport. In this case, such passports only serve transit travellers that pass through such countries. Also if the destination country has a low incidence rate, there are three possibilities. Either these countries have pursued a zero-COVID strategy (like New Zealand and Australia), or they are well underway to vaccinating their population. (Note that a country may simply have a low incidence rate because it is summer. This is not relevant for this analysis.) In the first case, COVID-19 vaccine passports give little assurance, much less than a recent infection test. And even then, visitors to such countries are required to go in quarantine. In the second case, a country that is well underway vaccinating its population will soon (after several months, but at most within a year) have vaccinated all of them (excluding the hopefully small fraction that refuse to be vaccinated). Once a country is fully vaccinated, it shouldn’t matter whether infected people visit that country or not: the effect on infecting the population should be small. Local people may get infected, but the vaccine prevents them from getting (seriously) ill. So only in this case, a vaccine passport might be useful, but for at most a year or so.
On top of that there are objections against the early use of COVID-19 vaccine passports as a requirement for travel or entering buildings, shops, malls or other establishments. When supply of vaccines is still short, and only a limited number of people have been granted the opportunity to get vaccinated, it is unfair to allow only this select group of people a greater freedom of movement. Especially because in most countries older, more vulnerable, people are vaccinated first while young, healthy, people - that have been denied access to proper education, sport, events and in essence have been denied to live the normal life of youth - are last in line.
Given this, COVID-19 vaccine passports seem to me to be an utter waste of time and effort.
And this is not even considering all the problem that will arise when implementing them, especially when going for digital vaccine passports (what’s wrong with the traditional yellow-cover paper-based one?). Privacy is first concern, of course. But also reaching a global standard quickly. Especially challenging will be to ensure that the authenticity of vaccine passports, issued by all these different countries or their health authorities, can be verified reliably. Because there will for sure be a huge market for fake vaccine passports as soon as they become a travel requirement.
(The introduction of the EU RFID/biometric passport a few decades ago does not instil any confidence, to be honest. Up to a few years ago, no country could/did check the signatures of the data on foreign passports!)