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- Hi, I'm Julie from the Exploratorium. Welcome to "Viral Questions," a series of videos where we answer your questions about COVID and vaccines. It feels like we're in another new phase of the pandemic. More and more people have been vaccinated, and yet there's a surge of COVID infections driven by a new variant of the virus named delta. Some of these new infections are taking place in vaccinated people, and today we'll look into why. A major factor in what's happening right now is the delta variant. In a previous video, I shared how mutations can arise in the spike protein that's on the surface of the coronavirus. Each variant has a collection of several mutations that alter how the virus behaves. One example is a mutation that changes the shape of the spike protein so that it binds more tightly to a target cell in your body. The variants, alpha, beta, and gamma all have a tighter binding mutation in their mix of changes. This mutation, along with others, has resulted in them being more contagious, with the alpha variant around 50% more contagious than the original SARS-CoV-2 strain. The delta variant has its own combinations of mutations in the spike protein. It's pretty straightforward for us to determine what those changes are, but much, much harder to figure out how those changes impact what the virus does. Scientists are actively trying to understand all of the mutations, and one has emerged that seems very important. In order to infect a cell, the coronavirus has to bind to a cell receptor, and then part of the spike protein gets cut in a way that allows the virus membrane to fuse with the cell membrane, so that the virus can spill its guts into the cell, and start to make more viruses. These viruses go on to infect nearby cells, and that's how the amount of viruses present exponentially increases. Now, delta appears to have a mutation that makes cutting the spike protein very efficient, which increases its ability to get into cells, and basically results in more viruses being produced than in other variants. This means infected people are producing more virus, which might make them sicker, and also increases the number that they could pass on to someone else, which makes the variant more contagious. Now remember, the purpose of getting vaccinated is so that you already have antibodies that can recognize and attack any SARS-CoV-2 virus that gets into your body. Even if you're vaccinated, though, if you breathe in a bunch of viruses, some might successfully infect some of your cells before your immune system can take care of them all. The more that get through, the more likely you are to experience symptoms related to COVID, and possibly pass the virus on to someone else. Because vaccinated people have immune systems that are primed for success, they usually experience mild or no symptoms, rather than developing a severe case of COVID before they're able to fight off the infection. Unvaccinated people are starting from scratch, so they're currently at tremendous risk, since a much more contagious variant has evolved, and they don't have a primed immune system ready to help them. Now, delta has other mutations that probably also contribute in ways we don't fully understand yet, but it's becoming clear that this variant is able to multiply so quickly and efficiently that even vaccinated people can pass on active virus while their antibodies go to work. The time that they're infectious seems to be shorter than it is for unvaccinated people. That makes sense since their immune systems are already trained to go, and they'll be able to manage the infection more quickly. Still, this is the reason behind recommendations that vaccinated people continue to use face masks, since they might be spreading virus, even though they don't feel sick. As the virus evolves, so will our knowledge about the impacts of each new mutation. One thing that's unlikely to happen is for a completely new virus to evolve, so the basic things we know about this coronavirus remain true. We know it's primarily transmitted through the air, so if you wear a mask, keep your distance, and interact with people only in well-ventilated places, you'll be doing your part to reduce its spread. If you're vaccinated, you're reducing the overall amount of virus you might produce if you get infected, which protects yourself and others. That's the best chance we have of getting out of this pandemic. Thanks so much for watching, and I'll see you next time.