The black sheep of the vaccine family just arrived in Ontario, the province revealing on Thursday that a limited supply of the single-dose Johnson & Johnson COVID-19 vaccine is now available as part of a final push to inoculate holdouts in the face of the threatening new omicron variant.

Approved by Health Canada back in March, this is the first mass-rollout of the Johnson & Johnson vaccines in the province, though it has been available on a limited basis for a select few for some time now.

News of the single-dose shots' arrival came in conjunction with the announcement of an expanded booster program that opens eligibility to anyone aged 50 and over starting in mid-December.

Freshly delivered Johnson & Johnson vaccines are aimed towards anyone aged 18 and over with an allergy or contraindication to mRNA vaccines, but those looking to get their vaccine in a single dose can also apply via their local public health unit.

But anyone racing to get in on this newly-offered one-and-done shot should be wary if other options are available, as all this convenience comes at a cost.

Unlike the mRNA vaccines that have become the most popular options in Canada, the Johnson & Johnson is a viral vector-based vaccine like the Oxford AstraZeneca shot.

And like the AstraZeneca vaccine, Johnson & Johnson's jab is said to offer less protection against the virus than phased Moderna or Pfizer shots, though it's much less of a headache with its simpler single-dose process.

Canada ran clinical trials showing the J&J vaccine was just 66 per cent effective in protecting trial participants against COVID-19, compared to 94 and 95 per cent respectively for twinned shots of Moderna or Pfizer mRNA vaccines.

Still, any protection is better than none, with Solicitor General Sylvia Jones saying, "Getting vaccinated is the best way to protect ourselves, our families and our communities."

Jones continues that this is why the province is now "providing Ontarians aged 18 or older who have not yet been vaccinated, with the option to request the Johnson & Johnson vaccine."