The vaccine developed by the U.S. pharmaceutical company Pfizer and the German biotechnology company BioNTech, also known as Comirnaty, uses messenger RNA (mRNA) technology. This is a technique that introduces laboratory-synthesised genetic material into human cells so that they learn to produce a protein, in this case, the Spike protein, which is found in the cover of the SARS-CoV-2 virus. In this way, the cells are made to manufacture copies of this protein and create antibodies to achieve immunity against the virus. 

Clinical trials began in April 2020 and the results were presented on 18 November. In total, 43,661 people participated, distributed among the United States, South Africa, Germany, Turkey, Argentina, and Brazil, according to data provided by the pharmaceutical company. Based on these trials, the pharmaceutical company reported an efficacy of 95%.

Pfizer’s vaccine is administered in two doses at an interval of 21 days. By the end of March, 79 countries had authorised its use, including the United States, the European Union, Australia, and the Persian Gulf states, and ten in Latin America, including Mexico, Colombia, Costa Rica, and Peru, as well as by the World Health Organization (WHO).

The most frequent adverse or side effects are pain in the vaccination prick site, fatigue, headache, muscle pain and chills, joint pains or fever, according to the European Medicines Agency. Up to one in 10 people may experience nausea or swelling at the injection site. Rare adverse effects (less than one in 100 people) include swollen lymph nodes, malaise, pain in the limbs, insomnia, and itching at the injection site. Facial paralysis is considered a rare side effect (one per 1,000 people) and no allergic reaction has been detected. 

Pfizer’s vaccine can be stored in a freezer for six months at a temperature between -80ºC and -60ºC. During five days it can be kept between 2ºC and 8ºC.

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