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With reports about the more transmissible Delta variant, and now "Delta plus," taking the media by storm, here are the essential facts when it comes to the latest variant in the spotlight.

What Is the Delta Variant?

The Delta variant, or B.1.617.2, first emerged in India, with the earliest samples dating to October 2020. However, it didn't raise alarms until India faced down a major COVID-19 surge this spring, when it became a variant of concern, according to both and .

B.1.617.2 is a variant of the first "India" variant, B.1.617 (named Kappa and only a variant of interest). There's also B.1.617.3 (variant of interest) and more recently, B.1.617.2.1, which has been called "Delta plus" in the media and doesn't yet have a spot on the CDC or WHO lists.

The chief concerning mutation in Delta is L452R, which changes the spike protein. "Delta plus" appears to have acquired the K417N mutation, which also changes the spike protein. Both variants also have several other mutations in spike, as well as other genetic changes that appear to have less of an impact.

Is Delta More Transmissible?

Delta does indeed appear to be more transmissible. The CDC cites a of 3,765 cases (household clusters), matched with 7,530 controls (single case in a household), to estimate the odds of household transmission of Delta compared with the Alpha variant (B.1.1.7), which first emerged in the U.K. This study found that Delta was 64% more transmissible than Alpha when it came to household transmission (95% CI 1.26-2.13, P<0.001).

Alpha was already estimated to be 50% more transmissible than the wild-type virus.

Is Delta More Virulent?

It's not clear if Delta causes more severe disease or leads to more deaths. Evolutionary biologists and virologists that there are many reasons why the epidemiology of virulence can be noisy -- if a surge is overwhelming a hospital, for instance.

Still, preliminary epidemiological work from England and Scotland suggests that Delta may be more virulent. of about 43,000 COVID-19 cases found an increased risk of hospitalization with Delta compared with Alpha (HR 2.26, 95% CI 1.32-3.89, P=0.003).

And a study by found that the risk of hospital admission was 85% higher in patients with the Delta variant compared with the Alpha variant (HR 1.85, 95% CI 1.39-2.47).

Do Vaccines Protect Against Delta?

Data from England and Scotland suggest that vaccines do still protect against Delta, though the variant does somewhat reduce their efficacy.

In its , Public Health England reported a 10% absolute reduction in overall vaccine effectiveness (two doses) against symptomatic disease with Delta compared with Alpha (79% vs 89%). As for hospitalizations, full vaccination offered similar protection against Delta (96%) and Alpha (93%).

A Public Health England study found that Pfizer's shot appeared to be more protective against symptomatic disease from Delta than AstraZeneca's jab (87.9% vs 59.8%).

from Public Health Scotland revealed similar results, showing substantial -- albeit somewhat diminished -- effectiveness against symptomatic infection with Delta. This study also found better efficacy with Pfizer's vaccine (79%) than for AstraZeneca's (60%).

Additionally, Moderna announced results from a that showed only a "modest reduction" in neutralizing antibodies against Delta with its mRNA vaccine.

"There are still breakthrough infections after vaccination -- and more so with Delta -- but current vaccines do still provide excellent protection against sickness and death compared to no vaccination," Christina Pagel, PhD, of University College London, told 麻豆传媒.

Do Monoclonal Antibodies Work Against it?

The CDC states that there's a "potential reduction in neutralization" by some of the currently authorized monoclonal antibody treatments.

Last week, the U.S. paused distribution of Eli Lilly's monoclonal antibody combination (bamlanivimab/etesevimab) due to poor performance against the Gamma (P.1) and Beta (B.1.351) variants.

that there's with its monoclonal antibody combination casirivimab/imdevimab. The same goes for GlaxoSmithKline and Vir Biotechnology's .

Are Kids at Greater Risk From Delta?

Parents especially have been asking whether the Delta variant poses a greater risk to children. While there are no data as to whether that's true biologically, experts are concerned about kids' vulnerability simply because they're not vaccinated yet.

Recently, infections in children , tied to the country's schools reopening in May. Still, there's no indication yet that Delta is more severe in kids.

Why Is Everyone Worried?

By the , only about half of the U.S. is fully vaccinated. This has experts worried that when fall arrives, Delta could be particularly problematic for those who still haven't gotten their shots.

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