"GB" wrote in message
...
On 04/02/2021 05:35, jon wrote:

The Oxford vaccine is made by taking a common cold virus (adenovirus)
from
chimpanzees and deleting about 20 per cent of the viruss instructions.
This means it is impossible for the vaccine to replicate or cause disease
in humans, but it can still be produced in the laboratory under special
conditions. By removing these genetic instructions there is space to add
the instructions for the spike protein from SARS-CoV-2. Once inside a
human cell the genetic instructions for the spike protein need to be
photocopied many times €“ a process known as transcription. In any
vaccine system, it is these photocopies that are directly used to make
large amounts of the spike protein.

Even though the adenovirus is harmless, I assume that our immune system
may become activated and recognise/destroy that adenovirus when the second
dose of vaccine is given?

Yes. it certainly does and thats why the accidental half first dose
in the Oxford trial got a much better result than with the intended
full first dose. And why the russian sputnik vaccine uses a different
adenovirus in each dose.

Once the spike protein is made, the immune system will react to it and
this pre-trains the immune system to identify a real COVID-19 infection.
So, when the person vaccinated is confronted with the SARS-CoV-2 virus
their immune system is pre-trained and ready to attack it.

Adenoviruses have been used for many years to make vaccines, and these
are
always tested to very high standards to make sure every batch of vaccine
has the correct copy of genetic instructions embedded in the vaccine.
However, thanks to very recent advances in genetic sequencing and protein
analysis technology, researchers at Bristol were for the first time also
able to directly check thousands and thousands of the €˜photocopied
instructions produced by the Oxford vaccine within a cell. In this way
they were able to directly validate that the instructions are copied
correctly and accurately, providing greater assurance that the vaccine is
performing exactly as programmed.

At the same time, the researchers checked the spike protein being made by
the vaccine inside human cells also accurately reflects the instructions
as programmed. This brand-new approach may be more routinely used in the
future to help researchers fine tune the performance of these kinds of
vaccines.