What Is Monkeypox and Should We Be Worried About It?

Cases of a rare virus related to smallpox have been reported in the US, UK, Canada and Spain. Here’s what we know

Monkeypox-like lesions are shown on the arm and leg of a female child.
By Therese Raphael and Sam Fazeli
May 19, 2022 | 10:27 AM

Bloomberg Opinion — While we no longer worry as much about the severity of Covid, there are questions about whether the pandemic has left us more exposed to other serious illnesses. Massachusetts officials reported a rare case of a virus related to smallpox, called monkeypox, on Wednesday. A small number of cases has also been reported in the UK, Canada, Spain and Portugal. Therese spoke with Bloomberg Intelligence senior pharmaceutical analyst Sam Fazeli about monkeypox and what we know so far.

Therese Raphael: How is monkeypox related to smallpox and how is it transmitted?

Sam Fazeli: Monkeypox virus comes from the same family as smallpox — the orthopoxviruses. It’s the most common of its family infecting humans after smallpox was eradicated. It was not really thought of as a distinct infection until it was detected in a patient who was thought to have smallpox in Democratic Republic of the Congo in 1972. The disease that is caused by the virus is similar to smallpox, with early fever, headache and fatigue, followed by a rash two to four weeks later. Monkeypox has an incubation period of one to two weeks, similar to smallpox. The average case fatality rate of monkeypox in unvaccinated persons has been reported at as high as 10%-13%.

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On transmission, the first thing to note is that monkeypox is a zoonotic infection, i.e. it goes from animals to humans, and it can infect a wide variety, but there is little detail on this. Human-to-human transmission of monkeypox is thought to be through saliva or respiratory droplets or contact with skin lesions, but it is not clear how efficient airborne transmission is. It is possible for the virus to be shed by infected individuals prior to them having skin lesions, suggesting that asymptomatic transmission can theoretically occur. While transmission is thought to be less efficient than for smallpox, there really haven’t been many epidemiological studies on this.

TR: There are two strains of the virus, one more serious than the other. What are we seeing so far?

SF: The Congo Basin monkeypox virus strain is more pathogenic than the West African strain, with higher morbidity as measured by lesion count and mortality, which for the former has been pegged at 10%–13% compared with 1% for the West African strain. So the good news is that, at least in the U.K., the cases so far appear to be of the West African strain.

TR: Does the fact that transmission is not airborne suggest we aren’t likely to see the kind of exponential growth in cases that we got used to with SARS-CoV-2? What sort of numbers would raise concerns about an outbreak?

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SF: There can be transmission through respiratory droplets, though this has not been studied extensively enough to be sure how efficient it is. Remember that the problem with SARS-CoV-2 was that it was also transmitted by aerosol, which can hang around in a room for much longer than droplets, which tend to fall to the ground relatively quickly. But given its mortality rate, even of the less virulent West African strain, and the fact that many younger people born after the 70s do not have immunity to the virus, even low rates of transmission can have dramatic societal impact.

TR: Do existing vaccines protect against monkeypox? Are there antiviral treatments that work for those who become ill?

SF: We have both. Two vaccines are approved for smallpox, though one has actually been approved for monkeypox. Bavarian Nordic’s Jynneos has been approved by the US Food and Drug Administration and many other regulatory agencies for both smallpox and monkeypox, whereas Emergent BioSolutions Inc./Sanofi’s ACAM2000 is only approved for smallpox, though is also likely to work against monkeypox.

The biggest difference between the two vaccines is safety, with ACAM2000 carrying a black-boxed warning on its FDA label about the risk of myocarditis/pericarditis, which was seen at a high rate of 5.7 cases per 1,000 people. There are other side effects that could preclude its broad use.

There are also drugs. Chimerix’s Tembexa capsules and liquid formulation, which the company is in the process of selling to Emergent BioSolutions, was approved by the FDA in June 2021 for the treatment of smallpox infections. It has shown activity against monkeypox in animal models, but I am not aware of data in humans. SIGA’s Tpoxx capsules were approved in 2018 and a liquid formulation has been developed since.

TR: The fact that we’re seeing this emerge now — is that pure coincidence or does that suggest the pandemic has weakened immunity enough to allow something like this to seed?

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SF: It has nothing to do with weakened immunity associated with the pandemic. You could say that about flu or the common cold virus or even Respiratory Syncytial Virus, but not this. What is likely going on is that the global level of immunity to orthopoxvirses has declined, as the last smallpox vaccination campaigns ended in the 1970s. As such, not only have a lot of people been born since and not been vaccinated with a smallpox vaccine, but also there is probably some decline in immunity against infection, even in those who did get a vaccine a long time ago.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

--Therese Raphael is a columnist for Bloomberg Opinion covering health care and British politics. Previously, she was editorial page editor of the Wall Street Journal Europe.

--Sam Fazeli is senior pharmaceuticals analyst for Bloomberg Intelligence and director of research for EMEA.