Why the Oxford Vaccine and the Russian Sputnik V Vaccine are effective

Coronavirus whose peplomer is shown in red. Many vaccines specifically target some of the viruses. credit: US CDC / Wikimedia Commons

There was some confusion when the efficacy of the Oxford / AstraZeneca vaccine was announced in late 2020. The overall efficacy of the vaccine to prevent the development of symptomatological COVID-19 two weeks after the second dose was 70%. But this was not the big picture.

This number is the average of the results for the two groups. In one group receiving the full dose of two doses vaccine It was 62% effective in stopping the onset of symptoms. However, in the second group, the dosing error meant that the volunteers received half the dose, followed by the full dose. This ultimately provided 90% protection against the development of COVID-19.

This was intriguing. Why does giving people less vaccine lead to a more effective immune response? The answer to this may be in the design of the vaccine, and it may mean that there are ways to make this vaccine (and others using the same design) more effective.

How the Oxford Vaccine Works

Vaccines work by exposing the immune system to the recognizable part of the pathogen that causes the disease, such as bacteria and viruses, or “antigens.” The immune system then begins to respond. Immune cells, called B cells, make antibodies that destroy pathogens. Occasionally, T cells act to eliminate our own cells infected with the pathogen.

After that, some B cells and T cells memorize future antigens. At some point in the future, if a person is exposed to a pathogen, these long-term memory cells can be ordered to quickly produce more antibodies to destroy the pathogen and attack the infected cells. ..

In effect, the principle of vaccination is to “mimic” an infection, but in a controlled way that immunity is generated without causing illness. After a few weeks, the production of T and B cells protects the vaccinated person. For some vaccines, this requires two doses, as the first dose alone does not generate complete immunity in some people. Booster doses ensure that as many people as possible get protection.

For coronavirus vaccines, many methods are used to present the viral antigens to the immune system.Some like Sinopharm and Sinovac vaccines In China, you only need to present the entire inactivated version of the coronavirus to your body. However, instead, some direct the vaccinated person’s own cells to produce a specific part of the coronavirus, a particularly recognizable antigen, the outer surface of the peplomer.

These vaccines do this by delivering a portion of the coronavirus Genetic code Encodes the spiked protein into the cells of the body and reads the code to start making the protein. Some, such as Pfizer / BioNTech and Moderna vaccines, deliver code in the form of messenger RNA (mRNA).Others use a harmless virus to put the genetic code inside cellThe Oxford vaccine uses a non-reproductive genetically modified chimpanzee adenovirus called ChAdOx1. These are known as viral vector vaccines.

How design affects effectiveness

It is not yet known why the Oxford vaccine weight loss regimen has shown better efficacy in trials, but it can extend to viral vectors.

When a person is given a viral vector vaccine and when it produces an immune response against CoronavirusPeplomer, Immune system It also initiates a response to the viral vector itself. This immune response, when subsequently delivered, can destroy some of the booster dose before it becomes effective.This has Has been recognized for a long time As a problem.

However, low initial doses may not generate a strong anti-vector immune response, leaving booster doses intact and increasing overall efficacy. If this turns out to be the case, future work will need to establish an optimal dosing regimen to generate the strongest immune response.

The Russian Sputnik V vaccine acknowledges that immunity to viral vectors can be a problem, but comes up with another solution.It use Two different human adenoviruses-Ad26 and Ad5 (out of 50 affecting humans)-the two vaccine doses. This heterologous (or hybrid) vaccine, which uses different vectors for prime and booster vaccination, makes it less likely that one jab will generate an immune response against the viral vector, which will interfere with the other. Therefore, the effectiveness of the vaccine is less likely to decline.

The Institute that made Sputnik V, Gamalaya Center, Said After two doses, the vaccine’s efficacy is over 90% (although no complete results have yet been published to substantiate this).This led to the AstraZeneca test. New hybrid vaccine A schedule that includes a single dose of the vaccine and a single dose of Ad26 Vector Sputnik V to see if the Oxford / AstraZeneca vaccine will be more effective.

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