What's the monkeypox vaccine and who should get it?

As the number of confirmed monkeypox cases continues to rise in Canada, infectious disease and public health experts are providing vaccinations to those at risk of infection.

Since monkeypox and smallpox are both part of the orthopox family of viruses, experts say some vaccines will work against both.

But the vaccines being recommended for use against monkeypox today are different from those used in the last century's global effort to eradicate smallpox, the World Health Organization (WHO) says.

"Some countries have maintained strategic supplies of older smallpox vaccines from the Smallpox Eradication Programme (SEP) which concluded in 1980," said the WHO's interim monkeypox vaccination guidance issued on Tuesday.

"These first-generation vaccines held in national reserves are not recommended for monkeypox at this time, as they do not meet current safety and manufacturing standards."

Monkeypox causes flu-like symptoms and skin lesions, and spreads through close contact.

Both WHO and Canada's National Advisory Committee on Immunization (NACI) have now released guidelines on what vaccine to use against monkeypox, and who might benefit from it.

The vaccine approved for immunization against monkeypox in Canada is MVA-BN, or Modified Vaccinia Ankara - Bavarian Nordic. Bavarian Nordic, headquartered in Denmark, is the company that manufactures it.

In Canada, the vaccine has the trade name Imvamune. (It's called Imvanex in the European Union and Jynneos in the U.S.)

Imvamune was originally authorized in Canada for "extraordinary use" against smallpox in November 2013, as part of the federal government's emergency plan to immunize people if the deadly disease were ever to resurface. In 2020, Canada expanded the vaccine's authorization to include immunization against monkeypox, NACI documents say.

Routine smallpox vaccinations stopped in Canada in the early 1970s. But because the viruses are related, those smallpox vaccinations may have provided some degree of immunity against monkeypox as well, experts say.

"It's likely that this, you know, mass immunization campaign for smallpox really kept monkeypox in check for many years," said Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital.

But most people under 50 in Canada didn't get that protection — and that might be one of the reasons we're seeing monkeypox now, he said.

Imvamune contains a weakened strain of the vaccinia virus, which provokes the immune response to fight off smallpox and monkeypox.