By Andrea Hargraves 
Assuming they are approved only after their efficacy has been demonstrated, all vaccines given against Covid-19 should be safe and useful to fight the pandemic. However, not all are the same, both in dosages and side effects, for example.
According to El Mundo, several factors characterize the Pfizer, Moderna, AstraZeneca and Janssen (Johnson & Johnson) vaccines.
How many doses are needed?
Pfizer and Moderna have developed vaccines that require two doses per person. In the case of Pfizer, the interval between doses is 21 days, while Moderna indicates a distance of 28 days between the first and second vaccinations.
From the beginning, citizens should be more protected from the effects of the new Corona virus, but the protection will not be complete until after the two doses.
AstraZeneca also requires two doses, this time 21 days apart. In this case, immunity only reaches 70% 14 days after the second dose.
Finally, Janssen has the distinction of being the only one of these four that only requires one dose to ensure immunity. The main advantage of this drug will be over others.
How effective are each of them?
According to the scientific journal The New England Journal of Medicine, cited by the Spanish newspaper El Mundo, the effectiveness of the Pfizer and Moderna vaccines is about 95% (95% for Pfizer / BioNTech and 94.5% for Moderna).
In turn, the U.S. Food and Drug Administration notes that Moderna’s vaccine is “highly effective,” although its efficacy declines slightly in the elderly — going from 95.6% in the 18- to 64-year-old to 86.4% in the elderly. Age group over 65 years old. However, given the data available to date, experts point out that it would not be possible to conclude that there is a difference in effectiveness depending on age.
Moving on to AstraZeneca, there is an average efficacy of 70%, according to data published in The Lancet, in December of last year. It can reach 62% or 90%, and the wide range is justified by an error in tests initially conducted with volunteers.
AstraZeneca ensures, however, that clinical trial results show robust responses, with adults producing 100% specific antibodies after the second dose.
About Janssen, a study of more than 44,000 people reports a 67% reduction in the number of symptomatic cases two weeks after the vaccine was given. Currently, the pharmacist is advancing tests with children and adolescents.
How do they work?
The Pfizer and Moderna vaccines are based on mRNA technology, which consists of inserting a set of genetic instructions from the coronavirus S protein into a nanocapsule that then reaches the body to stimulate an immune response.
In the case of AstraZeneca, the vaccine is based on a weakened version of the common influenza adenovirus that causes infections in chimpanzees. Scientists believe that this option generates a stronger immune response with just one dose, moreover, it is not a replicating virus, so it cannot cause persistent infection in the vaccinated person. This is a more classic approach.
As for Janssen, the vaccine originates from a viral vector that does not have the ability to reproduce, human adenovirus (type 26), which encodes the glycoprotein of the new coronavirus. This causes the immune system to recognize and attack the pathogen.
What are the side effects?
According to El Mundo, adverse reactions to vaccines generally do not exceed 40% of those vaccinated. The most common are injection site pain, fatigue, headache, and body aches, which usually do not last more than 48 hours.
Moderna is, to date, the most interacting vaccine, especially among young adults and after the second dose. Older adults, over 65 years of age, seem to react less to the vaccine.
However, AstraZeneca and Janssen are the two drug companies that are most frequently caused by very rare cases of blood clots. However, in both cases, the European Medicines Agency (EMA) determined that the benefits outweigh the risks.
What are the conditions for keeping each of them?
The Pfizer/BioNTech vaccine must be stored at -75°C ± 15°C, which poses some challenges for countries – although they are already developing a more “workable” version. Moderna indicates less demanding conditions for vaccination plans in each country, along with Oxford / AstraZeneca (which is also more economical).
In addition to requiring only one dose, Janssen also has a more favorable cooling temperature stability: it can be kept for three months between two and eight degrees. It can also remain valid for years if kept at -20 degrees.