One Strand? Or Many Strands?

Is there one strand (variation) of SARS-CoV-2, the coronavirus, out there? Or are there multiple strands? On 30^th April, a lab in Los Alamos, announced that a second strand “began spreading in Europe in early February”. And in Europe and the US, it rose in dominance, said the report.

First, let’s see why the multiple strands possibility seems probable to many. We’re told that evolution works through random mutations. A virus, with its short life span, reproduces very frequently. Thus, logically, over so many months, surely there must be multiple strands of the virus out there, right?

Ed Yong wrote this brilliant article on the topic, explaining why things aren’t that simple. Yes, he says, mutations occur. But to call a mutated virus a new strand, it must differ significantly from the rest. The keyword is “significantly”. Since we humans use that term wrt its impact on us, here’s what “significantly” means: (1) Easier to spread, (2) Increased ability to cause disease, (3) Ability to go unrecognized by the immune system, and (4) Higher resistance to medications. To summarize, a mutated virus isn’t called a new strain unless it has changed one or more of the above four fronts. Put differently:

“Not every mutation creates a different strain.”

The flu virus has always mutated rapidly. Luckily for us, the coronavirus family mutates at less than a tenth that speed. Yong points that while scientists have indeed detected multiple lineages of SARS-CoV-2:

“None seems materially different from the others.”

Wait a minute. If Yong is right, then how to we explain the Los Alamos finding? What started in Wuhan is called the “D lineage”. The new “G lineage” was first observed in February. And it is the G lineage which is most common in the West today. Given the havoc the virus has wreaked in the West (compared to China), it sounds like the G lineage is far more dangerous, right? Aha, says Yong:

“But this pattern is hard to interpret.”

Yong elaborates. Yes, it is possible that the G lineage is indeed more transmissible. But here’s another possibility, he says. The G lineage arose at a time (Feb) when China had initiated “intense social restrictions”, thereby preventing the G lineage from spreading in China. By pure luck, at the same time, the G lineage hopped onto its “initial continent-hopping pioneer” to reach Europe (and the West). In which case, the only reason the G lineage is common in the West is because it got there, not the D lineage!

Further, comparing the impact of D v/s G isn’t easy. You have to adjust for the age of people infected, their pre-existing conditions, access to hospitals, quality of healthcare etc. We simply don’t have enough data to do a valid comparison. Trying to do the study in cell cultures isn’t always helpful: you run the risk that what happens in the cell culture doesn’t happen in living things. Erroneous conclusions based on cell culture testing happened with the Ebola virus too, says Yong:

“The bottom line: It will take time to know whether different strains of the new coronavirus even exist, let alone whether any are more or less dangerous than the others. Any claims of that kind should be taken with a grain of salt for the next several months, if not longer.”

Like Yong though, I too feel most people are naturally inclined to believe in the multiple strand theories:

“If we believe that the virus has changed into some especially challenging form, we can more easily explain why certain people and places have been hit worse than others—a mystery whose answer more likely (but less satisfyingly) lies in political inaction, existing inequalities, and chance. Powerful antagonists make for easy narratives. Ineptitude, bias, and randomness make for difficult ones.”