So various media are reporting a new pandemic flu virus discovered in China.

What does this actually mean?

Let's look at the original paper. Actually, that's not so easy to do because—unconscionably in my opinion— @PNAS has put it behind a paywall. https://www.pnas.org/content/early/2020/06/23/1921186117

The paper reports on a surveillance project looking at flu strains in pigs in China from 2011-2018. Pigs are an important reservoir for influenza, which can jump from this species to humans wholesale or by genomic recombination with a human strain.

The main finding is that a new genotype of H1N1 flu, known as G4, emerged and by 2016 became the dominant strain in pigs.

So that's the first thing to notice. This is not a *new* new virus; it's been very common in pigs since 2016.

I should caution that it became the dominant strain *in the sample population*, which did not include all of China. Below, details from the supplementary information associated with the paper:

The study also finds that the virus is different enough from previous H1N1 strains that human populations would not currently be immune, should it start to spread. Moreover it has a number of characteristics that *could* make it well suited to spreading in humans.

It was formed by recombination between a previous dominant strain in swine, and the human 2009 H1N1 virus, and other sources.

The virus is capable of infecting humans, with two zoonotic cases briefly mentioned in the paper. Neither resulted in human-to-human transmission.

Swine-to-human transmission is probably far more common, however. About 10% of those working with pigs have antibodies to G4, whereas antibodies are rare in humans elsewhere.

So are we facing the start of a double pandemic, COVID + influenza?

Not immanently.

There's no evidence that G4 is circulating in humans, despite five years of extensive exposure. That's the key context to keep in mind.

The paper is not describing an immediate threat to the general public, despite news outlets running headlines that suggest otherwise.

The problem with the click-based advertising model is that there are strong incentives to get you to click.

What the paper does do is something important for the epidemiological community: it points to a virus that we need to be keeping a careful eye on.

That's something we can do. Screening will be important, particularly if clusters of illness emerge in swine workers.

But every indication is that the G4 virus would have to undergo some evolutionary change to spread readily in people, and it may never do that.

If it does? We know how to make vaccines for influenza viruses. It could be included in the seasonal vaccine; the only issue is timing.

So that's the G4/H1N1 story.

Worth watching for people in the field.

No immediate threat to public health.

For the time being, we can all get back to figuring out what we're going to do about the picture below.

That was fast:

https://www.nytimes.com/reuters/2020/06/29/world/asia/29reuters-health-coronavirus-china-pigs.html

. @angie_rasmussen goes into further depth about the paper: https://twitter.com/angie_rasmussen/status/1277731224354648064