With the coronavirus pandemic nearing its one-year mark and a slower-than-expected vaccine rollout beginning in many nations, some governments and companies are signaling that they will require vaccinations of international visitors or future customers.

United Kingdom cruise company Saga announced this week it will require all future guests to be fully inoculated by at least two weeks before their voyage. Some governments, including those of the Seychelles and Cyprus, have also announced they will reopen their borders and allow international visitors to skip quarantine only if they have received the vaccine. And this week the Biden administration issued an order calling for an assessment of international certifications of vaccination that could eventually be recognized by other nations requiring the shots.

The groundwork for a vaccine passport system is well underway and, in some ways, already exists. But should nations or companies require vaccines? And will the travel world at large follow suit? While vaccination requirements seem to be prioritizing people’s health, an increasing number of health experts and tourism officials are saying vaccine passports should not be made mandatory for international travel any time soon because of short supply of doses and potential lapses in the amount of protection vaccines provide; current health measures like testing and quarantines, they say, should stay for vaccinated people. And the World Health Organization recently said that it opposes vaccine requirements for travel because of equity issues in the current state of the global vaccine rollout.

“At the present time, do not introduce requirements of proof of vaccination or immunity for international travel as a condition of entry as there are still critical unknowns regarding the efficacy of vaccination in reducing transmission and limited availability of vaccines,” the organization said in a meeting statement last week. “Proof of vaccination should not exempt international travellers from complying with other travel risk reduction measures.”

The organization’s doctors are warning that a vaccine will not be a cure-all for travelers before there is global herd immunity — which will take years. WHO Global Outbreak Alert and Response Network chairman Dale Fisher said this month that global herd immunity will not occur by the end of 2021.

Requiring vaccines for travel is not a new concept: Many nations have long required inoculations against various types of illnesses, from yellow fever to polio, for entry. But because we know very little about the novel coronavirus and its current vaccines compared to illnesses that have come before, doctors say it is possible vaccinated travelers could still potentially harbor the virus and sicken unvaccinated people.

“The vaccines in the U.S. right now have not proven that they decrease transmission, so the patient may still get mild or asymptomatic versions of the disease and they may then be able to transmit it,” says Carlos Acuna-Villaorduna, an infectious-diseases physician at Boston Medical Center. “We also don’t know how long [vaccine] immunity lasts, so a vaccine or immunity passport could possibly give you a false perception of security from the virus that you might not have after a number of months.”

Outside of vaccine efficacy, there is also the problem of equity in distributing the much-needed vaccines globally, and not just to leisure travelers. Some officials say requiring vaccines could discriminate against those in nations where they are unable to be vaccinated soon, and it may drive vaccine availability down overall, which is an ethics issue.

“The World Health Organization doesn’t want [vaccine requirements for travel] because it’s a health equity issue,” David Freedman, an expert in travel epidemiology at the University of Alabama at Birmingham. “It is not fair to people in impoverished countries to have all the vaccine be used by rich people going on vacation instead of giving it to older people in poor countries.”

Doctors have warned that one in four nations will not see any coronavirus vaccinations this year. “The U.S., Canada, U.K. expect widespread vaccinations by the spring.” Acuna-Villaorduna says. “Countries in South America and Africa are way behind that right now. That’s not going to happen for people in those places until 2022 or so.”

Tourism voices have long been against required vaccinations, though for different reasons than health officials. Travel trade groups including the International Air Travel Association and Airlines for America have been calling for a uniform global approach to testing, not vaccines, that will allow travel to restart.

“The airlines are not in favor of mandatory vaccination — and their reason is a business reason,” Freedman says. “Since the vaccines are not widely available and airlines are a worldwide business, they don’t want to see that requirement because it’s going to take so long to get everybody vaccinated. If that was the main requirement their business is going to suffer for much longer.”

Increasingly, even voices encouraging the use of vaccine passports are saying they should not be a requirement for everyone. Prime Minister Kyriakos Mitsotakis of tourism-dependent Greece — who is leading the European Union’s campaign for a vaccine passport system for international travel — has said he does not plan to ban unvaccinated travelers. Instead, Mitsotakis has said that allowing free travel for those who are vaccinated would “provide an incentive” for more people to become vaccinated; he has not clarified what health protocols unvaccinated travelers would be subject to.

European Commission Vice President Maros Sefcovic has also said that vaccinations should not be required and that European travel protocols will include “different options.” European Union members are debating this week if it should begin to award greater travel freedom to those who can show proof of vaccination.

Outside of Europe, Canadian Prime Minister Justin Trudeau has also expressed disillusionment in requiring vaccinations. Trudeau said this month that some people may decline a vaccination for health or other personal reasons, and should be able to.

If vaccines do work to prevent transmission of the virus for a substantial amount of time, however, doctors agree that vaccine passports could be useful for those who are going to travel and nations that would welcome them back.

Despite its stance against mandating coronavirus vaccinations for travel right now, the World Health Organization already has a long-standing system for internationally recognized proof of vaccinations, called the Carte Jaune, or yellow card, which has been employed for required yellow fever vaccines in the past. European Union Commission President Ursula von der Leyen has noted that system in her recent public comments recommending that all vaccinated people acquire proof of their administered shot.

The main question is when and how those vaccination passports will be a responsible path forward for travel.

“In general, vaccines are the best way to help people return to some sort of normality we had before,” Acuna-Villaorduna says. “But it’s very unlikely that it’s going to happen soon.”

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