It is clear that vaccines against SARS-CoV-2 is one of the main current issues. Vaccines seem to be the only way to return to a “normal” way of life but, what kind of vaccine will we get? What are their differences? When will we get vaccinated? Will it end the pandemic? Will they give false positives in COVID tests?


What are Viruses?

In order to answer these questions and fully understand the effect of vaccines, we must first understand how viruses work.

Viruses are infectious organisms that enter the cells of a host – for example, us – multiplying within it.

Viruses contain genes that, by infecting our cell, “force” it to form new viruses – to create viral genes and proteins.  In other words, they use our cells as “factories” to multiply.

The presence of foreign intrusive elements causes our immune system to fire up and begin to recognize them, largely thanks to white blood cells (monocytes, T lymphocytes and B lymphocytes).


How do vaccines work?

Vaccines help us build immunity against viruses without having to go through the disease.

There are different types of vaccines (which we will discuss later) but all of them provide us protection by crearing against the vaccine T lymphocytes and B lymphocytes (which generate antibodies) that will remember how the virus must be fought in case of coming into contact with it again.

After vaccination, mild reaction symptoms may occur, such as fever, which are perfectly normal and a sign that our body is working and producing defenses.

Let’s not fotget that we do not become immune immediately, it can take several weeks to produce these T and B lymphocytes, so during that period of time we are susceptible to becoming infected and passing the disease.

This is one of the reasons why we should still be cautious after vaccination and follow all current sanitary measures.


What kinds of vaccines are there against COVID-19?

It is clear that vaccines produce defenses against the virus in our body, but there are differences in the mechanism of action that each one uses to achieve that immunity. In the case of COVID-19, 4 types of vaccines have been developed to date:

  • Messenger RNA (mRNA) vaccine: These contain genetic material from the virus, which is introduced into our cells and “forces” them to produce viral proteins; harmless to us and exclusive to this virus. The body recognizes this protein as an intruder and we generate antibodies. Once this process has passed, the cells destroy the genetic material of the virus that was in the vaccine.

The vaccines of this type that we have heard the most about are Pfizer / BioNTech and Moderna, both licensed in Europe. There is another pending authorization, CureVac.

  • DNA vaccines: They contain DNA plasmids that are introduced into cells, transferring the genetic information they carry to the RNA of our cells. From this point on, they act in a similar way to the previous ones.

These vaccines are currently only being produced in Japan (AnGes-Osaka U.) and India (Zydus Cadilla).

  • Protein subunit vaccines: These include safe portions of proteins from the virus that causes COVID-19. The body recognizes these proteins as foreign and builds immunity against the virus.

We have heard these types of vaccines named as Novavax and Sanofi Pasteur / GSK. In Canada, Medicago has also developed one of this type.

  • Vector vaccines: These use an attenuated version of another virus -the type responsible for the common cold- that has been modified so that it cannot replicate and that contains the genetic information of SARS-CoV2, which causes the proteins of the virus to be produced. viruses that cause our body to create immunity.

In this type of vaccines we find the already known AstraZeneca / Oxford and Janssen / J & J, although there are also others: Gamaleya (Russia) and CanSinoBio (China).

  • Inactivated virus / live vaccine: The virus is inoculated in a weakened or inactivated version so that it is recognized by the body. This is the traditional way of vaccination.

At the moment in Europe no vaccine of this type has been authorized. However, in the rest of the world we find: Sinopharm (China), Sinovac Biotech (China) and Bharat Biotech (India).

The European Commission is in negotiation of a total of 7 vaccines in different stages of development, corresponding to Spain a total of approximately 10% of the negotiated doses.

Of these 7 vaccines, 3 are already authorized by the EMA (European Medicines Agency):

  • Moderna: This vaccine of American origin uses mRNA. Spain has been assigned approximately 52 million doses. It requires two doses per person.
  • Pfizer / BioNTech: It is also an mRNA vaccine. Its use has spread widely throughout the US and Europe. It needs a temperature between -60ºC and -80ºC for its conservation. Approximately 16 million doses have been assigned to Spain. It requires two doses per person.
  • AstraZeneca / University of Oxford: Viral vector vaccine. Its use is not recommended in people with allergic conditions, nor in those under 18 years of age or over 55 years of age. Approximately 31 million doses have been assigned to Spain. It requires two doses per person.

On the other hand, there are 4 vaccines still under review by the EMA, which we hope will soon be available in Spain: Janssen / J & J, Novavax, CureVac and Sanofi Pasteur / GSK. All of them also require two doses like the previous ones, except the one from Janssen / J & J that requires a single dose.


And the tests? Can false positives occur in diagnostic tests for COVID-19 due to the vaccine?

The answer is no. The administration of anti-COVID-19 vaccines does not influence the results of diagnostic tests, so false positives are not possible in these. Another thing is the serological tests.

When we talk about diagnostic tests, we refer to antigen and PCR tests. In these it is not possible to obtain false positives. As we have already commented in previous blogs, in both tests a small sample of the mucosa is collected with a swab in which, in the case of PCR,  we search for the virus genetic material  and, in the case of the Antigens Tests, the presence of virus proteins.

Although vaccines incorporate or generate part of the genetic material of the virus and / or its proteins, these are not found in sufficient quantity in our body, nor do they invade our nasopharyngeal mucosa. In other words, the anti-COVID 19 vaccines have an effect at the local level, where the vaccine has been administered and it is not possible that the viral material can reach the respiratory tract in detectable quantity.

Diagnostic tests are designed to detect if the virus is present in the mucosa and if we are infected. That means that, if after being vaccinated, you get a positive result in a PCR or an antigen test, it is because you are infected with the SARS CoV-2 virus, not because of the vaccine, but a true positive.

However, antibody tests or serological tests (ELISA) look for the defense antibodies that we generate against the virus and, as we have commented in this post, the operation of vaccines is based precisely on the generation of these same antibodies.

That is, as vaccines what they do is, precisely, help us to generate those defenses, if we do an ELISA test or a Rapid Antibody Test after being vaccinated and it tests positive, it is very likely that what it is detecting is the antibodies generated by the vaccine, not an infection.

In short, and given the uncertainty that the pandemic still generates, we must continue to maintain all possible prevention measures, as well as carry out COVID-19 detection tests in case of any minimum doubt of contact with a positive or symptoms.

At Life Length we offer all types of tests 7 days a week.


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