Covid-19: What you need to know today

The big news of Monday is, of course, on Page 1 of this paper -- on the Pfizer-BioNTech mRNA vaccine being at least 90% effective in preventing Covid-19 according to the first interim analysis of late stage trail data. Pfizer’s CEO termed it a “great day for science and humanity,” and history may well prove him right, although there are still a few hurdles the vaccine has to clear. If it does that, it may well be available by the end of the year (See front page).

But this column isn’t about vaccines; it is about spillovers.

David Quammen’s 2012 book, Spillover: Animal Infections and the Next Human Pandemic, and the chapter on AIDS from it, later published as a separate book, The Chimp and the River: How AIDS Emerged from an African Forest, are among the best reads on zoonotic diseases. A spillover is an infection that originates in a non-human species but spills over into humans. In the case of AIDS, as Quammen chronicles, everything began with one “bloody encounter” between a Cameroonian hunter and an infected chimpanzee. In the case of Mers (Middle Eastern Respiratory Syndrome), a camel figures somewhere in the chain. And in the case of Sars, the virus was traced back to civets (hunted for meat), and further back to a species of horseshoe bats. Sars-CoV2, the virus behind the coronavirus disease (Covid-19), is believed to have jumped from horseshoe bats, perhaps to an intermediary (pangolins are likely candidates), and then to humans, although this chain is still being investigated.

Spillovers are far more common than people think (to be fair, many of the zoonotic pathogens are common ones such as Salmonella), although there are times when a new virus emerges. The virus behind AIDS was new. As were those responsible for Sars, Mers, and Ebola. And, more recently, Covid-19. These are so-called black swan events that result in nightmarish scenarios – and, unfortunately, given indiscriminate commercial farming of animals for meat or fur, and rampant deforestation and hunting (the consumption of bushmeat is widely believed to be behind Ebola), they are becoming far more common than the generic term used to describe them would suggest.

There’s been a lot of interest in spillovers in recent days because of minks in Denmark. Minks are small carnivorous mammals that belong to the same family as weasels, otters, ferrets, and wolverines (Mustelidae). In Dispatch 151 on September 7, I wrote about Netherlands deciding to close its mink farms by next March ahead of a planned 2024 deadline following research by the Erasmus Medical Centre, Rotterdam, that showed workers in mink farms (the animals are farmed for fur) were infected by other workers, who passed on the infection to more workers, suggesting that the virus was anthropozoonotic (capable of jumping from humans to animals), apart from being zoonotic (capable of jumping from animals to humans) in the case of minks.

Last week, Denmark announced that it is culling the entire mink population of its farms – around 17 million – citing mutations in the virus as it jumped from humans to minks, and then back. Worryingly (and scarily), the country’s environment ministry said in a statement that state health authorities “have now found a mutation in tests from five mink farms in Northern Jutland and in tests from 12 persons, and testing shows that the potential vaccines would not work effectively on this mutated virus”.

The statement also clarified that “there is no evidence that those people infected with this mutation experience a more serious disease”. Denmark has already started sharing the results of its genomic sequencing of the mutated virus on scientific databases, and more research is needed to understand and confirm the effect the mutation has on the infectivity of the virus, the severity of the disease, and the response to vaccines under development.

This is the year that proved Murphy’s Law beyond doubt, so how worried should we be? The opinion of most experts is: not much (although they’d like to see more data); many think the link Denmark makes about the mutation and the effectiveness of vaccines may not be backed by research. It’s not uncommon for viruses to jump from humans to animals. And Sars-CoV2 is no longer a strange virus whose effect on the human body is unknown.

Still, it is 2020.