Due to the great similarity with the Pfizer-BioNtech vaccine, authorized two weeks ago, both in the technological platform used (mRNA), and in the reactogenicity and efficacy results, both products are quite equivalent.

There are subtle differences in the composition, particularly in the type of modification made to some letters (nucleosides) of the genetic molecule, in the composition of the lipid covering that covers it and in some salts that are added as buffers (buffers) to improve chemical stability.

Pfizer's vaccine has been licensed for use in individuals over 16 years of age, while Moderna's in individuals over 18 years of age. Both vaccines are already undergoing studies in the age group 12 to 17 years. Pfizer reported a 95% efficacy in preventing symptomatic Covid, determined within a week of the second dose, in 44,000 volunteers.

Moderna reported an efficacy of 94.1%, measured after two weeks of the second dose, in 30,000 volunteers. The efficacy for severe disease was 90% for the Pfizer vaccine and 100% for the Moderna vaccine. The efficacy in adults over 65 years of age was 94.7% for the Pfizer vaccine and 86.4% for the Moderna vaccine. None of the percentages indicated is statistically different from each other, since the confidence intervals (variation margins) intersect. In terms of protection, therefore, they are very similar vaccines.

Both require two doses, separated by 21 days in the case of Pfizer and 28 days in the case of Moderna. Each dose of Pfizer's vaccine contains 30 micrograms (0.3 ml), while Moderna's contains 100 micrograms (0.5 ml). These vaccines are relatively more reactogenic than traditional vaccines that are commonly administered to children and adults. The most common adverse reactions are injection site pain, fatigue, headache, muscle pain, joint pain, and low-grade fever, usually mild to moderate and resolving spontaneously in 2 to 3 days.

These transient discomforts are more evident after the second dose and in younger adults (vigorous immune system) than in older adults (immune senescence). Minor allergic reactions were observed in less than 1% of the participants.

Severe allergies (anaphylaxis) did not occur in the phase 3 studies, but after authorization they have been reported to date in eight people (all with a history of similar events in the past) out of more than 3 million already vaccinated globally (incidence current: 1 anaphylaxis for every 400 thousand immunized). In all cases, there was rapid recovery when treated with adrenaline.

None of these vaccines has been studied in pregnant or lactating mothers, so their use in these circumstances, particularly in the third trimester of pregnancy, should be based on the risks of contracting Covid in a given city. There is also no data in children. We still do not have information on the duration of protection in the medium and long term, on the need to reformulate the vaccine over time, on the prevention of asymptomatic infection or on the potential reduction in contagiousness of someone vaccinated who becomes infected.

These uncertainties make it imperative that all vaccinates continue to comply with biosafety measures until herd immunity is achieved or it is proven that immunization prevents the spread of a vaccinated person who carries the virus asymptomatically to others. Administration of vaccines against other infections should be done at least two weeks before or after receiving the coronavirus vaccine.

Both vaccines are heat labile, requiring transport and storage at freezing temperatures, minus 60-80 degrees Celsius for the Pfizer vaccine and minus 15-25 degrees Celsius for Moderna's vaccine. When thawed, the Pfizer vaccine should be used within a maximum of 5 days and the Moderna vaccine can last up to 30 days. Once reconstituted for injection, both should be administered on the same day, ideally in less than 6 hours.

Each vial of Pfizer gives for 5 doses, while the vial of Moderna gives for 10 doses. Panama will have the Pfizer vaccine in January or February 2021, as the government processed the acquisition of 3 million doses in progressive deliveries. Moderna did not want to negotiate because it does not yet have the capacity for large-scale production and, as it was subsidized by the US administration, it must first satisfy the demand from that country.

Other vaccines are on the way and are sure to be approved in the months to come.