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The vaccine is made by using another virus (an adenovirus) that has been modified to carry the gene that gives instructions for producing the S (spike) protein of the virus (the one the virus needs to be able to enter human cells). This adenovirus does not reproduce, nor can it cause any disease.
When we receive the vaccine, some of our cells read the instructions of this gene and produce the S-protein. Our immune system recognises this protein as being foreign, so it produces antibodies and activates T-cells (lymphocytes) to attack it. If we later come into contact with the SARS-CoV-2 virus, our immune system will quickly recognise it and initiate our defence response against the coronavirus.
A clinical trial was carried out with more than 44,000 participants in the United States, South Africa and Latin America. Half of them received the vaccine (vaccinated group) and half were given a placebo (control group).
Two weeks after the injection, the clinical trial showed a 67% reduction (eficacy) in the number of symptomatic cases of COVID-19 in the vaccinated group (116 cases out of 19,630 vaccinated) when compared to the control group (348 cases out of 19,691 unvaccinated).
The Janssen vaccine is not recommended for children under 18 years of age because there is currently no information about the effects on this age group. The EMA has reached an agreement with Janssen to conduct a trial on this population group at a later stage.
Studies in animals do not show any adverse effects in pregnancy. However, the vaccines used mostly in pregnancy are those containing messenger ribonucleic acid (mRNA), which are those from Pfizer and Moderna; so these are more recommended during this period.
In the United States, over 100,000 pregnant women have already been vaccinated with mRNA vaccines, and no safety concerns have been identified in either the mother or baby.
Based on the information available to date and accumulated experience, the vaccination of pregnant women is safe. This is especially recommended, given that SARS-CoV-2 infection during pregnancy increases the risk of complications and of developing severe COVID-19 during pregnancy. It can be administered at any time during pregnancy, and women planning a pregnancy can receive any of the COVID vaccines without having to wait between vaccination and conception.
Breastfeeding women can receive the vaccine without having to stop breastfeeding. Another benefit of vaccinating pregnant and breastfeeding mothers is that the antibodies produced are transferred to the foetus through the breast milk.
Most people who are vaccinated will not experience significant side effects. These may appear during the first week after vaccination. They are not usual after the first two days. The most frequent mild or moderate effects observed in clinical trials were (source EMA):e: EMA):
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Substantiated information by:
Antoni TrillaSenior Consultant Head of the Department of Preventive Medicine and Epidemiology
Eduard Vieta PascualPsychiatristPsychiatry and Psychology Head of Department
Gema Maria Lledó IbáñezMédico internistaServicio de enfermedades autoinmunes
Jacobo Sellarés TorresPulmonologistPneumology Department
Josep M. Miró Meda
Josep Maria PeriClinical psychologist
Maica RubinatSpecialist in Sports MedicineGeneral Secretary for Sport and Physical Activity of the Generalitat de Catalunya
Mariona ViolanSpecialist in Sports MedicineGeneral Secretary for Sport and Physical Activity of the Generalitat de Catalunya
Published: 12 March 2020
Updated: 12 March 2020
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