Proof of immunity? Pa. and N.J. aren’t making plans for vaccine ‘passports,’ but the topic is hot.

You’re vaccinated, excited, and ready to return to the world. But will you know whether people around you are vaccinated? Will you have to show proof of your own shots?

Weeks after the idea of vaccine “passports,” or credentials showing proof of immunity, captured the public imagination, the answer likely will depend on where you’re going. Pennsylvania and New Jersey aren’t planning to implement statewide systems, and the federal government has indicated it will be up to the private sector. So it remains to be seen whether requests for credentials or the use of an app, whether at sports venues, theaters, universities, theme parks, restaurants, or other locations, could become widespread.

Catching a SEPTA train? Taking the family to Hersheypark? No one will ask you about your vaccination status. But coming back to some of the region’s universities or entering certain events, you might need to have had a shot. And some places could make it optional, like at a Flyers or Sixers game, where there’s a chance you will be able to choose to sit in a section for vaccinated people.

Those in favor of a standard way of verifying vaccination say it could help fast-track the country’s reopening and provide peace of mind for Americans venturing back to normalcy, particularly if the system were accessible to all, including those without smartphones. Others say the idea comes with serious equity and privacy issues. And like many issues related to the pandemic, some critics and advocates have framed it along political lines, arguing the idea poses a threat to freedom.

Efforts are underway by many companies and organizations to create an app that would allow Americans to show they had been vaccinated or recently tested negative. Some have already created their own systems. Private businesses — whether airlines and sports venues or office employers and stores — could require proof of vaccination, just as various immunizations are already required for many educational institutions or for international travel.

The Biden administration has said development of a passport would be “driven by the private sector,” though the federal government would likely want a credential system to meet certain standards. Israel is already using its “Green Pass” to give vaccinated residents entry to businesses, the European Union is working on a digital pass, and several other countries are examining or implementing the idea, as are some international airlines.

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New York state made headlines nationwide in March when it implemented an app that shows whether someone is vaccinated or has tested negative; it’s optional but has so far been used by restaurants, sports venues, and other event hosts. Hawaii is also working on a “safe travels” pass.

Pennsylvania is not considering “anything like that,” Gov. Tom Wolf said in response to a question about passports at an April 7 news briefing, indicating it was up to the private sector.

“If a cruise liner wants to make sure everybody’s safe on a cruise ship and they say you have to have some proof you have a vaccine. … If [organizers of] a sporting event [say], ‘We want to keep our spectators safe,’ I’m not sure why the government would weigh in either way,” Wolf said.

New Jersey Gov. Phil Murphy has said that he’s “open” to the idea but that the state would follow federal guidance. He added: “I think there are real issues, including issues of equity. This is like any other government-issued passport. Particularly given that we are not there yet on our objectives of achieving equity with the vaccine rollout. We’ve made a lot of progress, but we’re not where we want to be yet or will be. … That’s a concern.”

As private companies, researchers, and states look at various ways of handling credentials and other countries also roll out verification systems, the idea has become culture-war fodder for conservatives in Pennsylvania and elsewhere who have cast it as a government-overreach flash point.

Republicans in Pennsylvania and New Jersey have introduced bills in the legislatures to ban their states from implementing passports, even though credentials have not actually been proposed by either state. Their counterparts in other states have done the same, and some Republican governors have issued executive orders to the same effect.

“The idea of so-called vaccine passports is an opening to unfathomable government intrusion into people’s personal lives,” Pennsylvania House Majority Leader Kerry Benninghoff (R., Centre/Mifflin) said at the end of March, referring to New York’s system and warning the commonwealth should not follow the same path.

A spokesperson for Wolf said that some Republicans were continuing “to politicize a global public health crisis” and that all elected officials needed to encourage their constituents to get vaccinated.

Republicans are much less likely to want the vaccine — 43% of those surveyed in a mid-April Monmouth University poll said they didn’t plan on getting the vaccine, compared with 5% of Democrats.

“Getting vaccinated is politicized. It would’ve been so much better if we just didn’t go there,” said Henry Raymond, a professor at the Rutgers University School of Public Health.

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The other major concern experts have about immunity credentials is the potential effect on vulnerable or historically disadvantaged populations. SEPTA, for instance, has no plans to sort riders by vaccination status because it would cause serious equity concerns, a spokesperson said.

“The key test has to be: Is this increasing inequity, is it maintaining it, or is it reducing it?” said Harald Schmidt, a medical ethics and health-policy professor at the University of Pennsylvania. “And it seems much more likely that such approaches will maintain or increase inequities.”

He said immunity certification could harm undocumented people, who could end up with limited employment options or be unable to get certificates without ID. It could also provide a false sense of security that would lead the public to prematurely drop other mitigation measures, and could perpetuate inequity for people who have difficulty accessing the shot and subsequently can’t get a passport.

Nationwide, 59% of Americans believed immunity passports should be issued as proof of vaccination, according to a survey by MyBioSource.com, a biotechnical products distribution company.

That number was lower in Pennsylvania, at 49%, and much higher — two-thirds or three-quarters of residents — in some other states. New Jersey saw 53% of residents in agreement.

Asked whether the city could impose more restrictions on people who are unvaccinated, Philadelphia Health Commissioner Thomas Farley said last week that it would be too difficult to implement a passport-type system giving people proof of vaccination.

“Right now, if you’re vaccinated, you get a card that is very easy to forge. And so I think it would just create a risky business of people creating fake vaccination cards,” Farley said. “Creating one that is really something that can’t be forged or can’t be faked is a huge enterprise.”

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Raymond, the Rutgers professor, said vaccine credentials may not be necessary if the country reaches herd immunity, which experts generally say could happen if at least 70% to 80% of the population is vaccinated.

“It would be nice,” he said, “if we got to a point where the epidemiologists could say, ‘Well, we’ve had enough people get vaccinated that we’re not going to have big outbreaks again.’”

Staff writers Allison Steele, Erin McCarthy, and Laura McCrystal contributed to this article.