A Medical Breakthrough
April 7, 2021
Pfizer-BioNTech’s COVID-19 vaccine was the first to be approved by the FDA, closely followed by Moderna’s vaccine a few days later. Both of these are the first few authorized mRNA vaccines, a significant accomplishment in the medical world.
According to the National Human Genome Research Institute, mRNA is a single-stranded RNA molecule that complements a gene’s DNA strands. It is responsible for leaving the cell nucleus with the DNA’s genetic information as a template to help other structures produce proteins.
While traditional vaccines prompt an immune response by putting a modified germ into the body, mRNA vaccines use a spike protein sequence to teach cells how to make a protein to stimulate an immune response and produce antibodies.
“The mRNA will carry the genetic information of the SARS-CoV-2 virus. When it is injected into the human body, the mRNA will be used as a template to translate into a protein,” said Chunling Wang, a virologist. “That will trigger the immune response, and the body will produce antibodies and other major effectors to protect us from future infection.”
Both mRNA vaccines require two shots, spaced 21 days apart for Pfizer and 28 days apart for Moderna.
“The big efficacy studies were done for Moderna and Pfizer with the idea of giving an initial vaccine called a prime, which gives your body the stimulation to make the antibodies, and then a boost, which is like a reminder,” Brainard said.
Jin expressed similar reasoning.
“From the clinical trial data provided by Moderna and Pfizer, the first shot couldn’t provide high enough protection, and that’s quite normal,” Jin said. “Memory cells will just stay in your body but not produce the antibody until your body faces a second round of the foreign antigen infection. Then, those memory cells will quickly respond and have a higher immune response compared to the first response. That’s called immune boosting.”
Due to the booster shot, Pfizer and Moderna both yield high efficacy rates — 95% efficacy for Pfizer and 94.1% efficacy for Moderna — for protecting an individual against the coronavirus after the second shot.
Storing mRNA vaccines prove to be a challenge, however. Pfizer’s vaccine must be kept in an ultra-cold freezer between minus 80 and minus 60 degrees Celsius. In comparison, Moderna’s vaccine must be kept in a freezer between minus 25 and minus 15 degrees Celsius. Furthermore, the vaccines cannot be stored again to use the following day.
“Once you thaw it, you have to use it within a limited time, so they are not that stable,” Jin said. “It’s pretty much impossible to deliver this kind of vaccine to the whole world, especially to a developing country.”