ViroBlogy

An in-press article in Vaccine that was tweeted by MicrobeTweets (well worth signing up to, BTW) has the intriguing title “Whither monkeypox vaccination?”

Now, some background to this: monkeypox virus is a rather nasty relative of smallpox (family Poxviridae; subfamily Chordopoxvirinae, genus Orthopoxvirus), meaning it is a large dsDNA virus (170-250 kb) with a complex structure.  The virus is endemic in remote forest areas in central Africa – principally in the Democratic Republic of the Congo – and naturally infects a number of animal species, including giant pouched rats (Cricetomys sp.), dormice (Graphiurus sp.) and African squirrels (Heliosciurus, Funisciurus), as well as laboratory monkeys, which is how it was isolated and got its name.

Monkeypox gets transmitted to humans by contact with infected animals: this includes by simple handling, as well as by exposure to meat and blood of butchered animals.  It causes a disease in humans that is very similar in appearance to smallpox, with a case fatality rate of 1-10%, but is apparently far less easily transmitted person-to-person.  It caused only sporadic and limited outbreaks in Africa and was of limited interest until an outbreak in the USA in 2003, which was linked to young prairie dogs kept in a pet store in close proximity to an infected Gambian pouched rat (Cricetomys gambianus) recently imported from West Africa. Seventy-three people were reportedly infected, among whom there were no fatalities.  The CDC recommends vaccination of people exposed to human or suspected animal cases with smallpox vaccine, as this protects animals from experimental lethal monkeypox challenge.

The Vaccine paper makes the point that the potential for monkeypox virus (MPX) to fill the disease niche recently vacated by smallpox was evaluated in the 1970s – and discounted, largely because human-to-human spread was inefficient enough for outbreaks not be self-sustaining – thus, although smallpox vaccine protected against MPX, the WHO thought there was insufficient justification to continue vaccination.

Now, however, the incidence of the virus in humans

“…appears to have markedly increased. In addition to diminished vaccine-induced orthopoxvirus immunity, there have been profound social and demographic changes that have increased human MPX exposures and the likelihood of severe disease. Recurrent civil war and subsequent economic decline have forced rural residents to flee deep into the rain forests for extended periods of time, disrupted traditional village life and increased dependence on hunting for sustenance, thus increasing exposure to animal reservoirs of MPX.”

So, in other words, people are getting a whole lot more exposure to sick animals.  Increasingly, by eating them.  The paper goes on to say:

“Although orthopoxviruses are relatively genetically stable MPX has diverged into two clades with different levels of virulence. As incidence rises, each new MPX infection provides an opportunity for viral evolution or adaptation that may result in a more virulent or contagious variant capable of sustained person-to-person transmission. These new circumstances merit a re-evaluation of the need for immunizing against MPX”.

So – that should be relatively simple, surely?  I mean, South Africa alone has millions of doses of smallpox vaccine safely frozen away from the 1970s?  Not so fast….

“However, in an era where the threat of smallpox is not imminent and there are conditions such as AIDS, tissue transplantation, and therapies for cancer and autoimmunity that cause immunodeficiency, the adverse events associated with live vaccinia are no longer considered acceptable for the general population.”

The paper goes on to mention how all sorts of supposedly safe new smallpox vaccines have been deposited into biodefence stockpiles, based on animal testing.

And there it is again – that word “biodefence”, in the context of human vaccines – implying that there is a “biothreat” to counter.  Specifically, in this case, the spectre of weaponised smallpox.

The authors go on to make reasonable statements about surveilling for monkeypox in central Africa, and vaccinating people at risk, and say that treatment options should also be investigated given that clinical diagnosis is relatively easy.

They also close with this:

“If immunization studies in developing countries are contemplated to support the licensure of orthopoxvirus vaccines for industrialized countries or for military purposes, then provisions from those countries or organizations should be secured to distribute successful products in endemic regions where the products were tested.” [my emphases]

I should hope so.  I should really, really hope so – because then one country’s biodefence interests could end up benefitting quite a few others, who are the ones who really need the product.  Now, while you’re busy with that, what about vaccines for Rift Valley fever, Crimean-Congo haemorrhagic fever and Chikungunya – which are actually far more serious a problem, in a much bigger geographical area?