Thread by @dgurdasani1

There have been recent reports of the mink farm related outbreak in Denmark which has received attention in the media, and has concerned many scientists, and health organisations. What's happening in Denmark now is important. Here's why. Thread.

who.int/csr/don/06-nov…

There have been reports of transmission related to mink farming across several countries over the past few months. The recent outbreak in Denmark suggests that a mutated strain of virus passed from minks to humans, and then spread across humans.

Mutations in SARS-CoV-2 occur regularly, and most have minimal or no impact on viral fitness, as far as we can see from the data. But animal reservoirs can be more important in this regard. Mutations in a virus occur randomly through natural processes.

When mutations confer a selection advantage to the virus, these strains predominate and are transmitted. This is important because the selection pressure in different species can be different, which can lead to viruses diverging substantially in animal reservoirs.

This means that viruses that are then transmitted back from animal reservoirs can be quite different from the predominant circulating strains in human populations. This is concerning because some mutations may help the virus 'escape' the immune response.

This phenomenon has been observed for several infectious diseases with animal reservoirs, and we see a different form of this (genetic shift and genetic drift) with the flu. These sorts of changes can influence vaccine efficacy if a different strain is used for vaccination

We don't yet know the implications of the genetic changes in the Denmark strain. Early reports from the WHO suggest that these may be less susceptible to neutralising antibodies, but this needs a lot more assessment.

Scientists and public health officials who find this concerning are not being sensationalist. It's true we don't know whether the implications of this particular strain or outbreak are serious. But the wider implications are very concerning.

We know that SARS-CoV-2 likely spread to humans from an animal reservoir. Movement between animal and human reservoirs is concerning because it indicates that new genetically divergent strains can be introduced into the population in the future.

Irrespective of this particular outbreak, it's the possibility of future outbreaks which introduce different strains back into the human population that's worrying from the perspective of vaccination, and potentially pathogenicity.

Worrying about this and acting in response to this is prudent and cautious, not an overreaction. In the face of uncertainty, we have no choice but to act immediately to contain the outbreak given its *potential* implications. This is in line with the precautionary principle.

It also means that we need to look carefully at farming practices, and transmission in this context, as this represents a threat in the future. It also highlights the need for far more surveillance among farms, and animals that we know can transmit to humans.

I think the reporting of this has been cautious, and balanced. Its right to be concerned about this. With these events, we need to really think ahead, and understand wider implications, rather than those just related to specific events.

To me, this also makes a clear argument for focusing on elimination. The more transmission there is in communities, the more likely these cross-over events will occur, and the higher probability that one of these events will be significant.

It's prudent to be concerned, and respond now, whilst there is uncertainty. This shouldn't be labelled as sensationalist or panicky.

It's important we take a long-term view on this, rather than just the implications of this specific incident.