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It is a vaccinespecifically indicated as a reinforcement dose (“booster”) for people already vaccinated (minimum 2 doses) against the SARS-CoV-2 coronavirus, to reinforce immunity and maintain the prevention of severe forms of COVID-19 in people older than 12 years.
The vaccine does not contain the whole virus (SARS-CoV-2 coronavirus) and so cannot cause COVID-19.
The vaccine includes mRNA adapted to both the original Coronavirus variant (called "Wuhan") and the Omicron variant, specifically the BA.4 and BA.5 types, predominant in recent months.
This booster dose is expected to provide broader protection against the different virus variants.
The vaccine contains a compound called messenger ribonucleic acid (mRNA) from both the Wuhan and Omicron variants. The mRNA molecule contains the instructions to produce the spike (or S) protein in the virus, which is what the latter needs to enter human cells.
After receiving the vaccine, some cells read the instructions on the mRNA and temporarily produce the spike protein. The immune system recognises this protein as foreign, then activates T cells (lymphocytes) and produces antibodies to attack it.
When people come into contact with SARS-CoV-2, their immune system has already been “trained” by the vaccine to quickly recognise the virus and start the defensive response against coronavirus.
Both the original and the bivalent vaccinehave been shown to be very effective in preventing severe forms of COVID-19, reducing the number of cases of hospitalised patients (both emergency and non-emergency) and significantly reducing mortality from COVID-19.
Laboratory tests indicate a significant increase in antibodies directed against both the original variant (Wuhan) and against Omicron (BA.1, BA.4 and BA.5) after receiving the updated bivalent vaccine.
Current vaccines do not prevent contagion or infection as effectively as they did in the beginning. This change is because the currently predominant Omicron variant (especially the BA.4 and BA.5 subvariants) is more transmissible and escapes the action of the immune system better than previous variants. Fortunately, the infection it causes is milder.
Preliminary data indicate that the booster dose may reduce disease transmission, at least for 3-6 months after administration.
It is important to try to better adapt our immune response through this vaccine update.
The vaccine has the same side effects as the original Pfizer vaccine. They are mostly mild and transient.
These effects may appear during the first week after vaccination. They are not usual after the first two days. Side effects of these vaccines are very well known, and are some of the most studied in the history of medicine.
The most frequent mild or moderate effects observed are:
The estimated incidence of myocarditis (inflammation of the heart muscle) or pericarditis (inflammation of the membrane surrounding the heart) in the 7 days after vaccination is 1.3-2.2 cases per 100,000 people per day.
These side effects are more common in young men (18-25 years of age).
They are usually clinically mild cases with complete recovery.
Allergy to the vaccine is very rare: 1-2 cases per 100,000 doses administered.
The vaccine is contraindicated in people who have had a clinically significant allergic reaction to a previous dose of the COVID-19 vaccine or to any of its components. Serious reactions can be: anaphylaxis, angioedema, generalised urticaria, asthma attacks and rhinitis.
The components that could be responsible for these reactions in people with a history of severe allergy to them are polyethylene glycol (PEG) and polysorbate, which are not included in the vaccine but is closely related to PEG.
Allergy to tromethamol (an excipient in the updated vaccine) is very rare. This excipient has not been associated with allergic reactions after vaccination.
Vaccination is not contraindicated in people with allergies to food (including eggs), medications, animals, insects, environmental allergens or latex.
As with all vaccines, it should always be administered under supervision and with all medical resources at hand to deal with a possible severe allergic reaction.
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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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