As the number of confirmed smallpox cases continues to rise in Canada, infectious disease and public health experts are providing vaccines to people at risk for infection.
Because smallpox and smallpox are part of the orthopox virus family, experts say some vaccines will work against both.
But the vaccines recommended for use against monkeypox today are different from those used in the global effort of the last century to eradicate smallpox, according to the World Health Organization (WHO).
“Some countries have maintained strategic supplies of smallpox vaccines from the Smallpox Eradication Program (SEP) which ended in 1980,” he said. Provisional guide to WHO smallpox vaccination issued on Tuesday.
“These first-generation vaccines kept in national reserves are not recommended for monkeypox at this time, as they do not meet current safety and manufacturing standards.”
Smallpox is caused by flu-like symptoms and skin lesions, and spreads through close contact.
Both the WHO and Canada National Immunization Advisory Committee (NACI) have now published guidelines on which vaccine to use for monkeypox and who could benefit from it.
What monkeypox vaccine is available in Canada?
The approved vaccine for monkeypox immunization in Canada is MVA-BN, or modified Vaccinia Ankara – Bavarian Nordic. Bavarian Nordic, based in Denmark, is the company that makes it.
In Canada, the vaccine has the trade name Imvamune. (Imvanex in the European Union and Jynneos in the US)
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 recurred. In 2020, Canada extended the vaccine authorization to include immunization against monkeypox, NACI documents say.
An employee of the Bavarian Nordic vaccine company is working in one of his laboratories near Munich, Germany, on May 24th. The company’s Imvamune vaccine is approved in Canada for monkeypox immunization. (Luke Barth / Reuters)
Routine smallpox vaccinations stopped in Canada in the early 1970s. But because the viruses are related, these smallpox vaccines may also have provided some degree of smallpox immunity, experts say.
“It is likely that this, you know, massive smallpox immunization campaign really kept the smallpox under control for many years,” said Dr. Isaac Bogoch, an infectious disease specialist at Toronto General Hospital.
But most people under the age of 50 in Canada did not receive that protection, and that could be one of the reasons we are seeing monkeypox now, he said.
How is Imvamune different from the old school smallpox vaccine?
Imvamune contains a weakened strain of the vaccinia virus, which causes the immune response to fight smallpox and monkeypox.
Unlike the original smallpox vaccine, this weakened virus does not replicate, that is, it cannot make copies of itself.
First-generation vaccines based on vaccine strain replication caused unpleasant side effects for some and could be problematic for immunocompromised people, said Dr. Zain Chagla, an infectious disease specialist at McMaster University in Hamilton.
In addition, the older generations of the smallpox vaccine are administered differently. Instead of a normal syringe, the healthcare provider uses a “bifurcated needle” with two points and puncture the skin repeatedly to get the dose.
Who should consider monkeypox vaccination?
Infectious disease experts say that right now, smallpox is not affecting the majority of the Canadian general population, although anyone can get the virus if they are in close physical contact with an infected person.
The LGBTQ community, especially men who have sex with men, have a disproportionate risk of infection in this outbreak, they say. Healthcare or laboratory workers who work directly with orthopoxviruses may also be at risk.
As a result, experts say smallpox vaccinations should be offered to at-risk populations as a precautionary measure. The vaccine can also be given to those who have already been exposed to someone with monkeypox, known as post-exposure prophylaxis.
In both cases, they say, the spread of immunization against monkeypox should be targeted.
“This is not a widespread vaccine for everyone; it is a risk-based vaccination,” Chagla said.
Bogoch agreed.
“I don’t think we’re close to starting, you know, vaccine campaigns for the general public,” he said.
“Right now, this should be a very focused and targeted vaccination campaign for people who have been exposed and for people who are at the highest risk of getting this infection.”
How many doses?
Both the WHO and the NACI recommend two doses of Imvamune, administered 28 days apart.
A possible exception, according to NACI guidelines, is someone who has been vaccinated against smallpox in the past. In this case, they could be given only one dose to act as a booster.
Are there potential allergens to the vaccine?
Yes. NACI says Imvamune includes the following ingredients:
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Traces of residual host (egg) DNA and protein cells.
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Tromethamine (Trometamol, Tris).
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Benzonase.
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Gentamicin and ciprofloxacin.