New swine flu enters the watchlist, July 7, 2020

New swine flu enters the watchlist

Virus surveillance in animals is an important aspect of pandemic preparedness to know what is out there and could cause zoonotic infections (jumps from animals to humans) or even represent pandemic threats. Researchers have concluded a surveillance study in pigs and identified a new reassortant H1N1 swine flu that shows the minimal characteristics for a virus with pandemic potential.

Here are some important facts to consider.

refseq: HA_A/California/07/2009
A/swine/Jiangsu/J006/2018 EPI_ISL_482259
H1 structure with amino acid differences between new G4 strain and H1pm09 highlighted in red

Is it a new virus outbreak now on top of COVID-19?

No. This virus was identified from a large-scale surveillance study on viruses circulating in pigs. There is no evidence that people are infected beyond sporadic cases in the pig industry. But it is very important to have this virus on the radar for pandemic preparedness.

Can it be detected with current methods if it were to circulate?

Yes. The G4 strain that has become dominant since 2016 has acquired the M segment from pdm09 viruses and thus has the same target for which common flu A primers have been designed. The virus would easily be identified as influenza A virus but further steps are needed to characterize it, based on HA, NA and other segments.

The Figures on the right show the distribution of differences across the HA structure and the antigenic regions are indeed very different even at the stem where "universal" antibodies bind. In short, existing natural immunity or current vaccines may not be cross-reactive. Fortunately, because the virus was found early, there is time to investigate it further and design new candidate vaccine strains if needed.

Does this G4 strain have pandemic potential?

Possibly. There is evidence that it can infect humans based on swine worker serology and occasional zoonoses caused by viruses with a related HA. The virus was found to be transmissible between ferrets, which is taken as a warning for possible transmissibility between humans. Given that most of the world population would not have specific antibodies against HA of the virus (the HA surface protein is only 78.6% identical to the closest recent human virus which is H1N1pdm09), population immunity is likely to be low.

Will this virus cause the next pandemic?

Possibly, but not likely. Influenza viruses have been – and always will be – a problem to watch out for. Reassortment of viruses at the animal-human interface continues to be a serious problem. This G4 virus is one of several swine viruses with zoonotic potential in the world. It is currently impossible to predict exactly which one will cause the next pandemic and therefore we need to respond to each identified threat and be prepared for any emergency response that might arise.