The United Nations is demanding world leaders arriving in New York for its General Assembly adhere to an “honor system” to attest they are fully vaccinated against the coronavirus.

But that mandate will be tested in the general debate’s very first moments.

Jair Bolsonaro, who contracted the virus last year and as recently as last week said publicly that he does not need to be vaccinated because he has naturally acquired antibodies, is scheduled to kick off the 76th U.N. General Assembly’s general debate on Tuesday.

It’s U.N. tradition that the president of Brazil speaks first — yet the body seems to have little ability or appetite to enforce the mandate if Bolsonaro enters the General Assembly Hall without first getting a shot.

“Everyone who has contracted this virus are vaccinated, even in a way that’s more effective than the vaccine itself. So don’t argue it,” Bolsonaro has said. Brazil has the second-highest covid-19 death toll in the world — behind only the United States — with nearly 590,000 deaths and 37 percent of its population fully vaccinated, according to Our World in Data.

President Biden is set to arrive in New York City on Monday before also giving a speech Tuesday at the opening of the general debate.

A U.N. official familiar with the matter, who spoke on the condition of anonymity because they were not authorized to speak publicly about security details, told The Washington Post that it will not bar unvaccinated people from entering its building and participating in U.N.-related events. New York authorities are providing free testing and vaccination and have said foreigners traveling to the city for the event must be vaccinated, but U.N. officials said they did not have the ability to enforce a vaccination mandate.

The United States, which serves as the host annually to the event at the U.N. headquarters, initially tried dissuading as many participants as possible from coming: In a letter sent in August seen by media outlets, the U.S. mission to the United Nations asked those who could to attend virtually to avoid turning the annual gathering into “a super-spreader event.”

More than 100 are expected to show up anyway, spokesman for the U.N. secretary general Stéphane Dujarric de la Rivière told The Post.

Separately, the spokesman said at a news conference that the vaccine “honor system” means that “by swiping a badge to enter the [General Assembly] Hall, delegates attest that they are fully vaccinated, that they have not tested positive for covid-19 in the last 10 days and have no symptoms.”

The pressure is on the United Nations as all New York City residents older than 12 must prove they have had at least one dose of a vaccine to attend large indoor events as of mid-August.

New York Mayor Bill de Blasio (D) said he had told António Guterres, the U.N. secretary general, that this rule does apply to the General Assembly Hall — and the United Nations, while initially reluctant, agreed to align itself with the policy. But some U.N. officials were not pleased with what they saw as an intrusion on the United Nations’ extraterritoriality.

The coronavirus rules at one of the top diplomatic events of the year underscore the vast disparities of the global coronavirus vaccine rollout.

While the United States has a plentiful supply of vaccines, nearly 57 percent of the world has not received any doses, according to Our World in Data.

A further complication for world leaders and their teams is the fact that in many countries, the only available vaccines are those that have not been approved by U.S. health authorities, including the ones produced by British-Swedish company AstraZeneca, Chinese companies Sinovac and Sinopharm, and the Serum Institute of India.

These have all been approved for use by the World Health Organization, and New York City allows proof of a vaccine approved by either the WHO or the U.S. Food and Drug Administration.

Dujarric, the spokesman, said that “the honor system does not specify which vaccine” and noted that all delegates traveling for the meetings are also subject to health requirements of the U.S. federal government and would also need to show proof of vaccination to enter certain places in New York City, such as restaurants and theaters.

The mandate has already inflamed tensions among some dignitaries. Russian U.N. Ambassador Vasily Nebenzya wrote in a letter last week that the mandate is “clearly discriminatory” and that the “rights of people who can not be vaccinated for medical reasons, status of those who have just recovered from the COVID-19 and have antibodies, rights of people who received vaccines that are not approved by CDC, etc.” should be taken into account. (Russia’s Sputnik V vaccine is not authorized for emergency use by the United States or the WHO.)

When asked about the Russian ambassador’s comment, de Blasio said at a news conference that “if their vaccine isn’t good enough, then they should go and use one of the other vaccines.”

The mayor, referring to clinics offering the single-dose Johnson & Johnson vaccine that the city plans to make available to UNGA attendees, added that “anyone who’s had a nonapproved vaccine can get one of the ones that we’re using here that are effective.”

Others may wish for stronger action. In the case of Bolsonaro, Brazilian author and U.N. Messenger of Peace Paulo Coelho tweeted that it “would be a victory to prevent the delegation of Brazil’s president from entering” the General Assembly Hall if he is not vaccinated.

John Hudson contributed to this report.