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# How Can Such a Tiny Virus Have Such a Big Impact?

It's hard to believe that something smaller than a soda can has shut down the world for the better part of a year, but if British mathematician Christian Yates is correct, it has.

Yates, a senior lecturer in mathematical biology at the University of Bath, was asked by BBC Radio 4 to calculate the size of all of the particles of the coronavirus, or SARS-CoV-2. A published expert in all things math, Yates offers a detailed explanation of how he came up with his conclusion on the website The Conversation. Suffice to say, he appears to have been thorough.

He started with how many people are infected, considered how long the infection lasts, and determined how many particles of the virus those people contain at any given point. His conclusion: The world has about 2x10¹⁷, or two hundred million billion, coronavirus particles. That sounds huge, but when you consider just how very, very small each particle is, you get the point: At most, a single virus particle is 120 nanometers in diameter. For comparison, a sheet of paper is about 100,000 nanometers thick. In other words, the entire pandemic has been caused by something you could barely see.

• Although SARS-CoV-2 (which causes Covid-19) and SARS-CoV (which causes SARS) are quite similar, the former virus binds up to 20 times more tightly to human cells, making it much harder to fight.

• The coronavirus can survive on plastic and stainless steel for several days, and even up to 24 hours on cardboard.

• Despite rumors to the contrary, warm, sunny weather does not prevent coronavirus infections, although sunshine can boost your vitamin D levels and help your immune system.