Bill de Blasio’s vaccine mandate in New York is nothing less than a grandstanding move by a lame duck and may last only a few days.

One telltale sign: He announced it Monday on MSNBC, which seems to be the primary venue for most of his policy pronouncements. He’s the "Morning Joe" mayor.

Keep in mind that de Blasio, whose presidential campaign utterly fizzled, is now planning to run for New York governor.

But his decision to impose a vaccine mandate on the city’s private businesses wouldn’t take effect until Dec. 27 — and he leaves office four days later.

Bill de Blasio

Mayor of New York City Bill de Blasio attends the opening of a vaccination center for Broadway workers in Times Square on April 12, 2021 in New York City. (Photo by Noam Galai/Getty Images)  (Noam Galai/Getty Images)

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What’s more, the incoming Democratic mayor, Eric Adams, has already said "we need to revisit" some of de Blasio’s mandates. He was on vacation in Ghana and a statement said he would evaluate the new rule after taking office.

I’ve spoken out in favor of Covid vaccinations, and the rate has jumped by a third since the emergence of omicron and wider approval of booster shots. But I understand the debate about mandates, and de Blasio has just given the Republicans fresh fodder about government overreach by the Democrats.

Democratic candidate for New York City Mayor Eric Adams reacts as he speaks at an election night party in Brooklyn, New York, U.S. November 2, 2021. REUTERS/Andrew Kelly (REUTERS/Andrew Kelly)

"Omicron is here, and it looks like it’s very transmissible," the mayor said in the television interview. But what experts don’t know is whether it’s more deadly than Covid-19 or the delta variant, or relatively mild.

New York City workers, like those employed by the federal government, are already covered by a vax mandate. This sweeping, first-in-the-nation rule would apply to private businesses, and--this is key--there is no testing option for those who decline to get the shots.

President Biden’s mandate would cover large businesses, but it has been blocked in court.

Just under 90 percent of New York adults have already gotten at least one shot, so this is as much about headlines as health care.

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How exactly would de Blasio enforce this? Hire a new army of vax police? He couldn’t exactly answer that by when asked by Mika Brzezinski, other than to muse about cooperation.

New York, New York (iStock) (iStock)

The city already requires employees and customers at restaurants, gyms and entertainment venues to be vaccinated.

De Blasio does plan to allow medical and religious exemptions, but no details have been released. It’s a huge task, with 184,000 businesses to be covered. Now the rules for restaurants and theaters will be extended to kids aged 5 to 11, which in effect would block families with young, unvaccinated children.

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That amounts to undue pressure on parents who may well be vaccinated themselves but are understandably hesitant about having children as young as 5 get the shots.

A New York Times reporter quoted Kathryn Wylde, head of a major city business group, as saying: "We were blindsided. There’s no forewarning, no discussion, no idea about whether it’s legal or who he expects to enforce it."

It’s hard enough trying to build public support for vaccinations, which have become embroiled in partisan politics, with participation rates much lower for Republicans than Democrats. This kind of heavy-handed move by an outgoing mayor isn’t going to help, even if it lands him a spot on MSNBC.