Driven by the introduction of the more infectious Delta variant, cases surged to a record of nearly 26,000 daily cases, over four times that of the wave before it. Then, as quickly as cases rose, they fell once again, and within two months of the peak, cases now rest at around 140 per day. Scientists are aware the rapid rise was due to the Delta variant, but they failed to understand how cases plummeted back down while other nations continue to battle against the virus. .

This protein has been previously shown to be a proofreading enzyme in RNA viruses – that is to say every time the genetic code of the virus replicates, nsp14 scans through the newly-created genetic material to make sure no errors have cropped up. Mutations in proofreading enzymes spell disaster for organisms that don’t replicate often, so in a virus (which enters the cell, replicates into thousands of virions, and bursts from the host cell in around 10 hours), a faulty enzyme would spell utter catastrophe. 

These mutations appear to contribute to a crippled virus that is unable to replicate, which could explain how the Delta variant simply vanished from Japan in a matter of months.  

The theory is certainly interesting but doesn’t quite explain why the crippled virus would outcompete the dominant strain