September 29, 2020

what we know about its safety and efficacy


If approved for use, the vaccine developed by the consortium led by the University of Oxford and the pharmaceutical company AstraZeneca will likely be one of the first to be distributed for prophylaxis against COVID-19.

Oxford vaccine produces an immune response against COVID-19, according to preliminary results

Oxford vaccine produces an immune response against COVID-19, according to preliminary results

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But do we know if it is safe, what side effects it can cause and, if it is effective, how it will protect us?

Lets start by the beginning. The ChAdOx1 nCoV-19 vaccine, developed by the University of Oxford, is made up of viruses that affect chimpanzees and have been modified to resemble SARS-CoV-2 (they have a component of their envelope, the S protein). Thus, when this vaccine is inoculated into our body, the immune system reacts as if it were the coronavirus, only without the slightest risk of developing the disease.

The tactic is not new: many of the vaccines we receive as children work the same way. The result is that the body prepares itself so that, if we do contract the infection, it does not produce the disease. Or in any case, if there is any effect, let it be as slight as possible. To put it another way, we “introduce” you to SARS-CoV-2 so that it is not a complete stranger to you.

With vaccination we not only manage to avoid the disease, but we also contribute together so that the virus is not transmitted. We protect ourselves and we protect others. A clear example that the strategy works is found in the recent polio eradication in Africa.

Safety and efficacy in experimental animals

Before starting human trials, the preclinical phase includes mandatory testing of the vaccine in non-human primates, usually macaque monkeys. They are the best model because their immune system is very similar to ours and they suffer from the infection in a similar way. In addition, once vaccinated they are deliberately infected to analyze if the vaccine works.

The Oxford researchers found antibodies against SARS-CoV-2 two weeks after inoculating the animals with the vaccine and were not found in those that had not received it, used as controls. Animals that had received double doses had more antibodies and did not observe adverse effects in either of the two groups. They also detected an increase in interferon as a sign of a good cellular immune response (T cells). These effects are what is intended to achieve in a vaccine.

However, after infecting them with SARS-CoV-2, all the animals had viruses in the respiratory tract, although none of them had pneumonia (according to the analysis of his lungs), or affections in other organs.

The conclusion was that the vaccine appears safe, without adverse effects, but it did not prevent the proliferation of the virus in the animals (they were infected and could transmit it), although it significantly reduced the disease.

But does it work in humans?

The results of the first human studies (phases I and II). In the trials, 543 healthy people (18 to 55 years old) were injected with the SARS-CoV-2 vaccine, and 534 people were injected with a different vaccine (meningococcus, which causes another disease). Why meningococcus? Because comparing results with something known and of proven efficacy provides very valuable information to test new treatments.

Subsequently, the level of antibodies in the blood of the vaccinated individuals was analyzed using serological tests (ELISA) at 28 days after vaccination. What was detected was a clear increase in antibodies from the level before vaccination. When injecting a second dose, the level of antibodies continued to rise, and it was also found that they reacted against the SARS-CoV-2 virus (neutralized it). It was also observed that at 14 days memory lymphocytes (mature T cells) increased, as in monkeys.

And what about your security?

To analyze reactions to the vaccine, part of the individuals was administered paracetamol before vaccination. The observed symptoms described in the figure are the usual ones shown by most other vaccines that have been shown to be safe for a multitude of diseases.

The maximum intensity of symptoms was manifested one day after vaccination. And they disappeared completely before 7 days. Although some reactions showed severe characteristics, in no case was hospitalization necessary. As for the second dose, it also produced some effect, but always milder.

The comprehensive monitoring of the health of the participants will last for one year. It’s one of the reasons it takes time to get a vaccine or drug definitively approved: to check the long-term safety and efficacy of the vaccine.

But there is still …

The researchers note that more tests are needed with more people with different characteristics of age (children and the elderly), health, etc. before you are sure that the vaccine is effective. In fact, the next phase is already in preparation, which includes the vaccination of thousands of individuals in Brazil, South Africa and the United Kingdom.

Why in those countries? Because vaccination in regions where it is currently easier to acquire the disease will allow obtaining the necessary data to complete the experimentation. The results and conclusions of these studies will determine whether the vaccine will be used for the prophylaxis of COVID-19.

Transparency and veracity

What seems indisputable is that the publication in scientific journals on how medicines and vaccines are being developed is a must. Mainly because it implies that these results are meticulously reviewed by other researchers to detect any failure or omission, granting the level of veracity that characterizes the advancement of science.

The current health crisis is making it possible to make known to the whole world the ins and outs of each of the investigations of new

vaccinations to be able to acquire a criterion on them. Society has suddenly become interested in scientific subjects that it did not understand a few months ago, such as the functioning of the immune system.

It should be noted that this is positive and exceptional. Moreover, it is a very important advance to bring scientific research closer to the whole of society, which is to whom it is addressed. On issues as important as health, and specifically vaccines, you must know how they work and how safe they are. One of the responsibilities of scientists is that this information reaches all of society, so that the irrational fear of vaccines does not gain ground.

This article was originally published on The Conversation. You can read it here.

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