There are two covid-19 vaccines made from messenger ribonucleic acids (mRNA) that are in phase 3 of clinical trials. One of them is the one developed by the modern US biotechnology company in collaboration with the National Institute of Allergy and Infectious Diseases, which has just presented the intermediate results of its trial. They ensure that the effectiveness of the compound is 94.5%.
These encouraging data indicate that they detected 95 cases of COVID-19 among the trial volunteers. Of these, 90 cases belonged to the placebo group and 5 to the vaccinated group, which explains the efficacy of almost 95%. They also indicated that 11 of the cases in the placebo group were “severe.”
This data is even more promising than Pfizer / BioNTech. Not only because its efficacy was 90%, but because they have not indicated how the cases were detected in the placebo group (mild, severe or asymptomatic). In any case, and given the doubts that the scientific community initially had about whether this new technology was effective, scientific and societal expectations are very high. We all hope that when the clinical trial is over and they are marketed they can give good protection.
What are the differences and similarities between Moderna’s vaccine and Pfizer’s?
Both vaccines have several similarities. First of all, its formula is based on the same technology. It uses mRNA to make the SARS-CoV-2 protein S.
Second, and in both cases, this mRNA is encapsulated in lipid nanoparticles. These protect the mRNA from degradation, maintain its integrity and promote its phagocytosis so that the cells that initiate immune responses can more easily capture them. Since they can bind to internal vesicle receptors that amplify signals, these vaccines generate a very strong immune response.
The third similarity is the route of administration, intramuscular. The fourth is the number of doses, two.
Finally, the side effects that both have presented are very mild: certain discomfort and swelling at the immunization site, small flu-like symptoms, headaches and slight fatigue.
However, the Moderna and Pfizer vaccines also have subtle differences.
Differences in its structural design
Although the goal of the mRNA in both vaccines is to produce protein S, it has two parts or subunits. S1 contains the entry cell receptor binding region of the SARS-CoV-2 virus, while S2 helps the virus-cell fusion to occur and infection begins.
Moderna / NIAID vaccine mRNA (designated mRNA-1273) produces a structural form of protein S that is just prior to membrane fusion of the virus and contains both S2 and S1 subunits intact. Pfizer’s (called BNT162b1) produces only the S1 subunit that binds to the receptor, a domain called RBD.
The consequence is that the type of immune responses that both mRNA structures originate may be slightly different , both in the antibodies they generate and in the cellular responses.
Differences in the formulation of the vaccine
While the Moderna / NIAID vaccine does not include in its formulation any adjuvant that amplifies the immune response, the Pfizer / BioNTech vaccine does. Even so, the formulation has not been indicated in the methodological data that they have shared with the scientific community.
In principle, the fact that good vaccination efficacy can be achieved with both formulations could indicate that one vaccine is somewhat more potent than the other. This should be seen once the full clinical trials have been completed and it can be seen in which groups one and the other work best.
Differences in dose spacing
The Pfizer / BioNTech vaccine consists of two doses that are 21 days apart. Those of Moderna / NIAID are also two, but spaced 4 weeks apart.
In principle, the difference is not much, nor is it foreseeable that this will cause different results.
Differences in its conservation
Another difference that both present is their conservation. While Moderna / NIAID’s vaccine can be stored under refrigerated conditions for one week and is highly stable at -20 ⁰C for up to 6 months, Pfizer / BioNTech’s has a storage temperature of -75 ⁰C, which in principle it makes transport somewhat difficult and implies that you will have to think about certain ways to solve this discomfort. It will also be necessary to see the possibility that it can be distributed in countries where these extreme conditions of conservation are not available.
Both questions remain unanswered: How long does immunity last? What aspects of Covid-19 disease are prevented?
Carmen Álvarez Domínguez, Biochemist and molecular biologist, professor of Health Processes at the Faculty of Education and researcher in Immunotherapy, UNIR – International University of La Rioja
This article was originally published on The Conversation. Read the original.
