When a pathogenic germ enters the human body, our immune system records the information and remembers it, in order to be able to carry out a rapid counter-offensive if this germ appears. In most cases of viral infections, this memory lasts a long time. But it’s not always the case.
The principle behind all vaccines is to give the subject a version of the germ which will not cause disease, but which will nevertheless remain in the memory of their immune system. This is achieved by various methods depending on the nature of the virus and the extent of our knowledge of the virus.
The two kinds of vaccines
Some vaccines are made to neutralize the pathogen so that it is safe when introduced, but still able to continue its natural life cycle. The idea is to stimulate a response close to that of the natural immune system in order to register it in long-term memory without making the subject sick.
It is the basis of the vaccine that is given against measles, mumps and rubella (MMR). It contains the living, but inactivated, elements of each of these viruses. It is given to children in two doses a few years apart, in case the vaccine does not work the first time: it must therefore be “reminded” in the memory of the immune system. This is not a booster vaccine as such, but rather a second dose in order to avoid possible interference with other childhood infections, and because a child’s immune system preschooler is still in the developmental stage.
This MMR approach is made possible because the measles, mumps and rubella viruses are very common in the population, and virologists have excellent knowledge of their interaction with the immune system. But it takes many years to create a safe and effective live vaccine, and that is why, in the case of SARS-CoV-2, research teams are taking different paths. In this case, an effective approach is to use a dead version of the virus rather than a live version, but modified as is the case with MMRs.
Inactivated polio and flu vaccines both use dead versions of the virus. The disadvantage of these vaccines is that the immune response does not last, and that is why it is necessary to use boosters.
In the case of seasonal flu, mutations in the virus require a new vaccine every year anyway, but even if the virus did not mutate, boosters would still need to be used to boost immune memory, as the virus does not. is not alive.
In the case of polio, most countries use an inactivated vaccine as part of their childhood immunization programs rather than its live version given orally. Since the disease has been virtually eradicated, it is assumed that an injection of just one dose per child should be enough to protect them when they start dating. But in the event of an epidemic, anyone in the close presence of other individuals in a local area should receive a booster vaccine.
What Would a COVID-19 Vaccine Look Like?
The possible vaccine designed by the French company Valneva, which will be manufactured in Scotland, is an inactivated vaccine. If it turns out to be effective in protecting us from SARS-CoV-2, it could certainly help reduce the spread of the virus.
In this case, boosters would undoubtedly be necessary, perhaps on an annual basis, in order to guarantee the sustainability of the immune memory. In the event of an epidemic, everyone in the infected area could receive a dose of the vaccine to limit transmission.
Another vaccine design involves extracting the genetic code from the part of the virus that is known to stimulate an immune response, and inserting it into a carrier organism that cannot cause disease.
The hepatitis B vaccine uses the code for the antigen found on the surface of infectious particles of the virus. This code was introduced into the genome of a harmless yeast to make a vaccine. As it expands, the yeast divides, communicates its antigenic properties to the surface of the virus, and therefore prompts the body to elicit a continuous immune response. Given in three doses over a six-month period, this vaccine requires a booster after about five years for most people.
The COVID-19 vaccine developed by the team at Oxford University, and with promising initial results, basically uses this approach, as the researchers extracted the spike protein code from SARS-CoV- 2 to graft it into a harmless virus vector.
It is therefore possible that the initial schedule for anyone treated with this type of vaccine involves one or two booster doses a few months after the first dose, as is the case for the hepatitis B vaccine. We are not some of the immune duration in the case of COVID-19 under this strategy, but it could be measured in terms of years by analogy with hepatitis B. This may be enough to contain the spread of SARS-CoV -2.
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