1/ THREAD: Can differences in the genetic makeup of the #COVID19 virus affect its severity? This is a hugely important question that has major implications for how we approach public health measures and vaccine development. nyti.ms/2Biis3n
2/ A few weeks ago I asked what factors might explain why some people have severe Covid illness and others have mild symptoms or none. I continue to think strain differences may be contributing to the differences seen in severity around the world.
3/ Mutations are common in most viruses as they spread, including in enveloped RNA viruses such as SARS-CoV-2. Even if only a small proportion of the genome has changed, we’re not always sure what that small part does, especially in a new coronavirus.
4/ Remember Zika? There’s growing evidence some strains are more likely to cause birth defects than others. bit.ly/2YNKUSu
5/ One mutation in Covid, known as D614G, is associated with worldwide dissemination of the coronavirus, but it’s not yet proven to have any association with severity. bit.ly/3daYhBI
6/ This mutation in the Covid spike protein, pictured here, makes the virus more stable—so perhaps both more infectious and more lethal. It’s common in NYC strains. But...that’s still just a theory. We need more data to confirm or refute. 
7/ Here's why this matters: if some strains of an infectious virus such as Covid are more or less lethal, that changes the risks and benefits of the public health measures we put in place to control it, such as physical distancing.
8/ Mutations can also give us a clue for how to develop vaccines. Perhaps less severe strains are less likely to cause late complications such as inflammatory syndrome in children.
9/ There's much more to be learned. The key is to combine molecular analysis and detailed epidemiology. Real-time sequencing could also help find and stop chains of transmission. And, if some strains are more dangerous, identify when more intensive control measures are needed.
