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The Delta variant of Covid-19 is highly contagious.
About 60% more easily passed from person to person than the Alpha version or B.1.1.
Delta variant B.1.617.2
The basic reproduction number around six for Delta, meaning that, on average, each infected person spreads the virus to six others.
The delta variant is the most able and fastest and fittest of such viruses.
It may also cause more severe disease in people who are not vaccinated.
Having an Alpha, Beta, or Gamma variant modestly increased the odds that an infected person would become seriously ill with COVID.
The Delta variant raised the risk even higher, increasing the odds that an infected person would need to be hospitalized or could die from their infection by 50% compared to older variants, regardless of vaccination status.
The Delta variants have about 15 different mutations compared with the original virus.
There are mutations to the spike protein that appear to help the virus escape the antibodies made to fight it.
The P681R mutation appears to enhance the “springiness” of the parts of the virus that dock onto cells, som it’s more likely to be in the right position to infect cells if they come into contact with it.
P681R may also enhance the virus’s ability to fuse cells together into clumps: fused cells are called syncytia.
The syncytia that Delta creates are larger than the ones created by previous variants.
Large syncytia may help the virus copy itself more rapidly, so a person’s viral load quickly builds, or may enhance the ability of the virus to transmit from person to person.
Delta variant of the coronavirus is racing through the country and now is responsible for 83% of all U.S. cases.
A large increase in COVID-19 cases, has occurred in areas with low vaccination rates.
People infected by Delta tested positive earlier than their predecessors had.
In 2020, it took an average of 6 days for someone to test positive after an exposure.
With Delta, it took an average of about 4 days.
When first testing positive, there is more than 1,000 times more virus in their bodies, suggesting the Delta variant has a higher growth rate in the body.
If people are shedding 1000 times more virus, it’s much more likely that close contacts will be exposed to enough of it to become infected.
Shedding earlier in the course of their infections, allows the virus has more opportunity to spread.
Its ability to form syncytia may help the virus hide from our immune system, and it may make the virus more damaging to the body.
When a virus infects a cell, it will corrupt the cell’s protein-making machinery to crank out more copies of itself.
Upon the death of the cell these new copies are released into the plasma outside the cell where they can float over and infect new cells.
It’s in this extracellular space where a virus can also be attacked by the neutralizing antibodies our immune system makes to fight it off.
Antibodies do not penetrate inside the cell.
Delta variant is also able to escape antibodies made in response to vaccination more effectively than the Alpha, or B.1.1.7 strain.
This effect is more pronounced in older adults, who tend to have weaker responses to vaccines in general.
Individuals who have a mild infection of Covid-19 have protection against the virus for at least a year and that vaccinating these individuals substantially enhances their immune response and confers strong resistance against variance of concern including the delta variants.
A single dose of vaccine is only about 31% effective at preventing illness with Delta, and 75% effective at preventing hospitalization.
After two doses, the vaccines are still highly effective, even against Delta, reaching 80% protection for illness, and 94% for hospitalization.