The European Union’s much anticipated coronavirus digital certificate, which is intended to facilitate unrestricted movement across the continent for vaccinated travelers, will begin Thursday amid widespread confusion about how the rollout will go.

But many vaccinated would-be travelers — particularly those from poorer countries — do not meet the program’s criteria because they received AstraZeneca shots produced by India’s Serum Institute, which has not been approved by E.U. regulators.

The Serum Institute, however, is approved by the World Health Organization and is a major supplier to the Covax initiative, which is intended to ensure an equitable distribution of coronavirus vaccines and is a main procurer of doses for many poorer countries.

As of Wednesday, only four Western-produced vaccines qualify under the E.U. certificate’s criteria: Moderna, Pfizer-BioNTech, Johnson & Johnson and AstraZeneca doses, also called Vaxzevria, manufactured in Europe by AstraZeneca, which developed the vaccine with Oxford University.

Not on the list is the Serum Institute’s AstraZeneca vaccine version, called Covishield, as it is not approved by the European Medicines Agency, the European Union’s medical regulatory body.

WHO and Covax issued a joint statement Thursday criticizing as “counter-effective” vaccine travel certificates that do not include all WHO-sanctioned versions.

“Any measure that only allows people protected by a subset of WHO-approved vaccines to benefit from the re-opening of travel into and with that region would effectively create a two-tier system, further widening the global vaccine divide and exacerbating the inequities we have already seen in the distribution of COVID-19 vaccines,” the statement said. “It would negatively impact the growth of economies that are already suffering the most.”

It continued, “Such moves are already undermining confidence in life-saving vaccines that have already been shown to be safe and effective, affecting uptake of vaccines and potentially putting billions of people at risk.”

Serum Institute chief executive Adar Poonawalla said Monday that he was working to resolve the issue as fast as possible. The institute has applied for EMA authorization.

“I realize that a lot of Indians who have taken COVISHIELD are facing issues with travel to the E.U.,” he said on Twitter. “I assure everyone, I have taken this up at the highest levels and hope to resolve this matter soon, both with regulators and at a diplomatic level with countries.”

The Serum Institute’s shots are chemically the same as those produced in Europe.

The European Union’s coronavirus vaccine passport is intended to provide a streamlined way for vaccinated travelers to bypass quarantines and ensure they are virus-free. But because each E.U. country can set its own rules for entry, there are concerns that a lack of coordination could hamstring the program.

Under the rules, which are not obligatory for member states to follow, each country can also choose to waive quarantines for travelers vaccinated against the coronavirus with versions approved by the WHO.

The Covax initiative has distributed more than 89 million vaccines to 133 mainly low- and middle-income countries across Africa, Asia and Latin America.

On Tuesday, the African Union warned that Africans could face discrimination because the majority of Covax-procured AstraZeneca shots delivered on the continent have been produced by the Serum Institute. The current E.U. rules would therefore still classify many vaccinated Africans as effectively unvaccinated.

The WHO has cautioned against using vaccination as a travel prerequisite, given the widely unequal spread in vaccine availability between Western and wealthy countries compared to poor and lower-income ones.

This report has been updated.

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