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Several COVID-19 variants are acting uniquely enough to qualify as a distinct strain. And you might have heard about one on the news: the Delta variant. Today we’re going to talk about what it is, why it’s here, and what you need to know about it.

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This episode was filmed on August 10th, 2021.

For more updates on the COVID-19 pandemic, check out our playlist linked in the description. [♪ INTRO]. Ready for some COVID news?

Yeah, I know, me neither. But we wanted to talk about something that’s been in the news, and that you may even have questions about: the Delta variant. So in this episode, we’re going to talk about what it is, why it’s here, and what you need to know.

The Delta variant is a strain of the SARS-CoV-2 virus, which is the virus that causes COVID-19. It’s one of several variants that’s acting unique enough to qualify as a distinct strain. Those get Greek letters for names right now, like Beta and Gamma, plus the first dominant strain: Alpha.

Since it was identified in late 2020, it’s quickly becoming the dominant strain in many parts of the world. That includes countries that had successfully managed earlier strains and relaxed public health measures, like the United States and France. And what makes this variant worrisome is that it looks like it’s more easily transmissible than previously dominant strains.

The World Health Organization says that the Delta variant is the most transmissible of the variants identified so far. We don’t yet know why it’s able to spread so much more readily, though. One study has proposed that it’s because infected people have higher viral loads, that is, more copies of the virus in their bodies.

If true, that would mean that the Delta variant reproduces faster and is more infectious at early stages than other dominant variants. This variant may also affect our bodies differently than previous dominant versions of the virus. The study I mentioned also suggested high viral loads may be related to a shorter incubation time, meaning infected people show symptoms faster.

However, this paper has not yet been published or passed through peer review, so we’ll need further confirmation. Other data indicates that the Delta variant’s symptoms might be slightly different, with headaches, fever, sore throat, and runny nose being common while cough and loss of sense of smell aren’t. It also comes with some new symptoms, including hearing loss.

But are those infections more severe? Well we’re not sure yet. Some experts say that may be likely, and there are some reports that the Delta variant may be more likely to lead to severe illness compared to other strains.

And a report from Scotland suggests hospitalization for unvaccinated individuals is twice as likely if the patient is infected with the Delta instead of Alpha variant. It might be that the Delta variant is more dangerous. Or that it’s spreading faster through more vulnerable populations.

And easing up of public health measures has certainly played a role as well. The situation in India seems to have been a perfect storm. Their vaccination campaign was just starting to get going.

Officials had relaxed restrictions on large public gatherings, and that plus the heightened transmissibility may have let the. Delta variant spread through the population rapidly. But it’s not a simple matter of India relaxing social distancing and other public health measures.

Because here’s where we run into another wrinkle:. In Australia, most of their public health measures, like contact tracing and social distancing, have been seen as a model worldwide. And the Delta variant has punched right through them.

Relatively speaking, anyway. For most of 2021, Australia has managed under 100 new cases a week, but since July, that number has skyrocketed to around 2000 a week. That’s still low compared to some countries, but it’s pretty troubling.

What Australia hasn’t had, so far, is a high vaccination rate. But even vaccinated individuals may need to be wary. There’s been a lot of attention paid to so-called breakthrough infections, which is where someone who has been fully vaccinated still gets sick.

There have been a few well-documented outbreaks that included a substantial number of vaccinated people. Now, it’s worth noting that some breakthrough cases are expected. No vaccine is ever perfectly effective at preventing infection.

It’s worth the reminder that most of the vaccines in use right now were first tested around their ability to prevent severe disease, not necessarily stop transmission. Later on, we did begin to see evidence suggesting they could help halt the disease, but that wasn’t actually the primary goal. And while we don’t have much in the way of separate data for the Delta variant, overall, it does appear that the vaccines we have are still working by that measure.

They’re helping to prevent severe disease and death. Data from the World Health Organization suggests that a number of vaccines, including Moderna, AstraZeneca, and SinoVac, have so far been over 80% effective against severe disease, hospitalization, and death. So the question becomes whether the Delta variant is more likely than others to infect vaccinated people.

And whether those people would go on to spread it. And I said we didn’t have much data concerning vaccines and the Delta variant, but we have some. A paper published in July in the New England Journal of Medicine suggested that two doses of both AstraZeneca and BioNTech-Pfizer’s vaccines are effective against the Delta variant.

They lost only a few percentage points of efficacy compared to an older strain. Now, both of those vaccines are administered in two doses. And the paper did find that only a single dose of either was less effective against the Delta variant, dropping from about 50% to only about 30%.

That seems to be the case for other variants as well. Altogether, it is possible for someone who is fully vaccinated to be infected with any variant. According to the CDC and some pre-print data, people with breakthrough infections of the Delta variant may have a viral load just as high as someone who isn’t vaccinated.

And remember, the Delta variant might come with a lot. This has raised concerns about how much vaccinated people might still spread the infection. Though it’s worth noting that high viral load isn’t necessarily an indication of heightened infectiousness.

It could be that those viral particles are present in the body, but have been deactivated by the immune system. So they’re not actually a problem. And as more people get vaccinated, the proportion of breakthrough cases to normal cases will rise, because the proportion of vaccinated people to unvaccinated people will rise, and you can’t have a breakthrough case unless you’re vaccinated.

That’s what it is. So, what can we do? Well, we don’t yet have a lot of concrete answers regarding the Delta variant.

But remember that vaccines still seem to work. And by “work”, here, I mean they help limit severe illness, hospitalization, and death even if people do get sick. Some of the vaccine manufacturers are looking into booster shots, but many public health experts say they would rather focus on getting to people who haven’t yet had an opportunity to get even a first dose.

And this isn't just a question of logistics, but equity, as most of the available vaccines have gone to rich countries so far, leaving many vulnerable populations waiting. And we still do have all the stuff we had at the start of the pandemic. I’m talking about you’re quarantining if you’re feeling sick, you’re washing your hands, all that good stuff.

These will continue to be an important part of limiting spread as much as possible. We can see from Australia’s example that social safety interventions like distancing aren’t bulletproof. But vaccines, in the absence of those same measures, aren’t enough either, because breakthrough infections happen, and a lot of people remain unvaccinated.

It’s going to take a comprehensive strategy to stay ahead of this thing. Meanwhile, experts are keeping an eye on this and other variants, like Lambda, which also appears to be more infectious and possibly resistant to vaccines. Unfortunately, even though we all really, really would love to believe otherwise,.

COVID isn’t over yet. Thanks for watching this episode of SciShow. We hope it brought a little clarity to the confusing ongoing situation we find ourselves living in.

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