A higher number of vaccines are currently available worldwide, in order to of the herd immunity that will allow us to finally combat the pandemic caused by SARS-CoV-2. These vaccines have been developed differently, and the work with different methods to achieve the same objective.
We can define three main methods for designing a vaccine, which differ in terms of whether they use the whole virus, only fragments of it, to provoke the immune response in our body, or only the genetic material that will generate virus proteins for the same purpose.In the method in which the whole virus is used, it has to be inactivated or attenuated, so that it produces a reaction from the immune system, but the disease does not appear. Viral vector vaccines can also be included in this typology.
In the method that uses only a fraction of the virus (called genetic subunits), fragments necessary to activate the immune response are used, and these fragments are usually proteins or carbohydrates. Finally, the genetic approach, or mRNA vaccines, uses a sequence of genetic material that will give instructions to our cells so that virus-specific proteins are made, recognised by the immune system, and a memory is generated to respond to them in the future.
Vaccines are the key to put an end to the pandemic caused by the Covid-29 disease, more and more are being developed every day and many of them are showing excellent results in this regard.
The availability of more than one effective and safe vaccine is the key to this path. In this sense, the efforts of researchers and pharmaceutical companies around the world should not become a competition, because the number of available vaccines must be large enough to maintain herd immunity around the world, as a single company could never supply all countries in terms of production capacity, time, and resources. Recurring questions in this regard are: if there is more than one, which is the best vaccine? and why there are two-dose and one-dose vaccines? is the one-dose vaccine better than the two-dose vaccine?
The answer is simple: there are no better or worse vaccines. Having several options with different specificities makes it possible to administer the most appropriate one according to the individual and the situation, and there will be probably soon third dose vaccines available in search of herd immunity, which is the key to ending the global risk situation. Several vaccines against covid-19 are needed to make up for the shortcomings of others, in order to address factors such as seasonality, or the diversity of geographical, health and social variants.
From the beginning of the Covid-19 vaccination phase, it was clear that vaccines can and have prevented severe coronavirus disease, with cases of severe hospitalisation being significantly reduced, as well as mortality, which means that the effects of covid are milder if you have been vaccinated.
However, it still remains unknown whether vaccines could reduce infection and the transmission of the virus. As far as we know, we could transmit Covid-19 after being vaccinated. While it is clear that currently available vaccines are not ‘sterilising’, which means that they are not preventing virus replication, some recent studies provide very positive data on the ability of available vaccines to also reduce infection and transmission.
Worldwide vaccination against Covid-19 is still in progress, with more than 458 million doses administered in more than 150 countries, according to Our World Data. However, health organizations approve drugs at different times in different countries, and not all territories receive all vaccines.
Vaccines act in our organism by developing immunity against the SARS-CoV-2 virus, without individuals having to suffer from the disease it produces (Covid-19), and that is the reason why we could feel tired after the vaccine and suffer from some of the Covid-19 symptoms.
However, it has not been determined yet how long the immune response that is generated lasts in the long term, that is to say, we do not know how long the memory of our immune system lasts. In order to answer these and other outstanding questions about SARS-CoV-2 immunity, serological studies are being carried out worldwide to determine the degree of immunity of each vaccine and its duration over time. As far as we know from the vaccine developers, vaccines reduce the effects of covid, but they do not produce immunity, and even if you have been vaccinated you can not be in contact with infected people.
Currently, there are some studies already available that have evaluated the memory of T and B cells 6 months after infection, showing that memory cells (T lymphocytes) were found in 90% of cases. Furthermore, B lymphocytes have also been assessed in several studies 6 months later and these memory cells specific for spicule protein, RBD and nucleocapsid were detected in the subjects studied and increased over time.However, it is important to continue studies in this regard, especially around the different vaccines administered, in order to determine all outstanding responses in this regard.
Almost all vaccines are proving to be able to generate an adequate immune response against the variants that have emerged. However, there are exceptions, a study published in the New England Journal of Medicine showed that AstraZeneca’s vaccine does not work against the South African variant B.1.351.
Not all vaccines available and licensed so far have the same response to the different variants or strains currently known. The Pfizer and BioNTech vaccine, for example, has demonstrated to be effective against both the African and British variants. Moderna’s vaccine has also shown to be effective against the British variant, according to another published study.
Research on vaccines and their effectiveness against the different variants is not yet closed and there are no conclusive answers in this regard, given that immunology is very complex, and the virus has not yet been sufficiently researched to predict its behaviour accurately, so it is essential to continue doing exhaustive serological analysis to detect and monitor the evolution of the virus.
The evidence available so far shows that the results of diagnostic tests do not give false-positive results after vaccination. The vaccines available, as we have seen, are messenger RNA or inactivated viruses, and they do not enter our system through the respiratory tract, so they are not detected in the mucosa, which is what is used as a sample in a PCR, for example. On the other hand, the techniques used in PCR tests are specially developed so that this does not happen.
As for antigen tests performed with the same mucosal sample, there is no reason to think that this could affect the results, for the same reason, according to what has been observed so far, it is not possible that the proteins that are developed with the vaccine can reach the respiratory tract in a detectable amount.
On the other hand, it is posible to get covid after being vaccinated, before the second dose, this is because the vaccine have not completely been applied, and the immune system is not protected yet.
Viral load is the amount of virus an infected person has in their blood, which is expressed as a number of viral particles per millilitre of blood. Applied to SARS-CoV-2, a higher viral load is associated with more severe implications and symptoms, and decreases as the infection progresses, which can be used to monitor and assess disease progression in individuals. Moreover, a study published in ‘The Lancet’ showed that patients with a high SARS-CoV-2 viral load increase the risk of transmitting the virus by 12-24% and develop symptomatic disease more frequently.
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