Thread by @RayMax_99

#DeltaVariant

❓How Delta enters cells
To infect cells, SARS-CoV-2 must enter the body and bind to receptors on the surface of cells. The virus is studded with mushroom-shaped spike proteins that latch onto a receptor called ACE2 on human cells.

This receptor is found on many cell types, including those that line the lungs. Think of it like a key fitting into a lock.

Mutations that help the virus bind more tightly can make transmission from one person to another easier.

Imagine you breathe in a droplet that contains SARS-CoV-2. If that droplet contains viruses with better binding capabilities, they “will be more efficient at finding and infecting one of your cells.”

❓How it infects once inside
But better binding not only lowers the threshold for infection. Because the virus is better at grabbing ACE2, it also will infect more cells inside the body.

The infected person will have more virus in them, because the virus is replicating more efficiently.

After the virus binds to ACE2, the next step is to fuse with the cell, a process that begins when enzymes from the host cell cut the spike at two different sites, a process known as cleavage.

This kick starts the fusion machinery. If binding is like the key fitting in the lock, cleavage is like the key turning the deadbolt. Without cuts at both sites, the virus can’t get into cells.

One of the mutations present in Delta actually occurs in one of these cleavage sites, and a new study that has not yet been peer reviewed shows that this mutation does enhance cleavage.

Whether that improves transmissibility isn’t yet known, but it could. When scientists delete these cleavage sites, the virus becomes less transmissible and less pathogenic. So it stands to reason that changes that facilitate cleavage would increase transmissibility.

It’s also possible that Delta’s ability to evade the body’s immune response helps fuel transmission. Immune evasion means more cells become infected and produce more virus, which then potentially makes it easier for person carrying that virus to infect someone else.

❓Is vaccines still work
Vaccination provides strong protection against Delta:
• The Pfizer-BioNTech vaccine was 88% effective in preventing symptomatic disease due to Delta in fully vaccinated people.

• The AstraZeneca vaccine provided slightly less protection. Two shots were 60% effective against the variant. The effectiveness of one dose of either vaccine, however, was much lower— just 33%.

https://twitter.com/RayMax_99/status/1397909915096604673?s=19