Editors Note: This week, Machine Design will be sharing a series of articles addressing the development and distribution of the COVID-19 vaccine–and the obstacles crossed the path. Be sure to check out the other allowances below:
The U.S. health care system, with help from the rest of the government as well, is now in the process of vaccinating everyone in the U.S. against the COVID-19 virus, which will give two injections of the vaccine given. about three weeks apart. That means manufacturing, delivering and injecting more than 660 million doses.
Pfizer and Moderna have both developed vaccines, but the delivery to a network of planes and trucks – and perhaps even drones – that will take them to where they can be used and used poses engineering challenges.
Vaccine differences
The Moderna and Pfizer vaccines are the first two of their kind approved for use. Until now, vaccines contained dead and weak forms of the crime virus, its toxins or surface proteins. They start the patient’s immune system to initiate antibodies made specifically to attack and kill these agents, thus preventing the patient from becoming dangerous at the time. future. Such vaccines can help patients fight off viral infections as well as prevent them from becoming ill in the first place.
Both new COVID vaccines use messenger ribonucleic acid (mRNA). This type of RNA is used to carry out instructions on how to regenerate proteins from the DNA that is protected inside the nucleus of the cell to the areas of the cell, the cytoplasm, where the protein is to do. As soon as the mRNA does its job, it decays rapidly.
For the vaccine, the mRNA has instructions for picking up copies of the spike protein of the coronavirus, not the whole virus. Human cells read that instruction and secrete copies of the protein that, in turn, activates the immune system to produce antibodies that attack the coronavirus if it comes to call. And because the vaccines contain no parts of the virus, just instructions (genes) for making the spike, theoretically patients cannot be infected from the vaccine. The mRNA never enters a cell nucleus, so it cannot damage the patient’s DNA.
MRNA vaccines can also be made faster and cheaper than traditional vaccines because yeast or bacteria do not have to be used to make and cleanse the COVID spike gene. The formula for mRNA vaccines is easier to develop; researchers just need the genetic sequence of the pathogen to start making and then test the vaccine. For example, Moderna received a vial of COVID-19 virus from China in January 2020, and ordered their genes in just a day. So within two days, the company had everything it needed to plan and design the vaccine.
In the vaccine, the mRNA is covered with a protective lipid shell that protects the mRNA from breaking down naturally until it enters cells to deliver its load. Then the immune response begins.
This is where the Moderna vaccine benefits. The company has already developed 10 mRNA-based vaccine candidates and has more experience in designing the lipid shell to best retain the mRNA fragments. This means that it can be safely stored for up to six months and removed at −4 ° F (20 ° C) without reducing the mRNA. It will also be stable for up to 30 days if maintained at 36 ° to 46 ° F, normal home or medical refrigerator temperatures.
This cooling rate (−4 ° F) is common in today’s “cold chain”, the global supply network of vehicles and warehouses used to transport and transport drugs and other healthcare products. distribution as well as food.
However, the Pfizer vaccine has a different protective lipid shell and appears to have a different formula for its mRNA; must be maintained at −94 ° F (−70 ° C), beyond what is normally handled by cold chain infrastructure. Fortunately, dry ice, with a surface temperature of around −110 ° F (−79 ° C) can be used in packing vaccine filters and keeping it cool enough.
And both vaccines require patients to receive two doses about three weeks apart to get the full effect of a vaccine.
mRNA and Cold Temperatures
There are at least three suspect factors in determining the potency of the mRNA vaccine and the amount of cooling required for it to be active and effective. How pharmaceutical companies deal with these factors, which they are not likely to reveal, then determines how cold the vaccines need to be kept.
DNA and RNA differences: DNA has a molecular backbone of sugar deoxyribose; The RNA backbone is made up of ribose, a sugar with one more oxygen molecule than deoxyribose, making it much more stable than DNA. As a result, DNA can survive for generations while RNA is short-lived and immobilized.
RNA killers: Once mRNA does its job, transporting the genetic guide for a protein from the DNA to where it is needed in the cell, a series of enzymes in the cell and the livers break down. down the RNA relatively quickly. This helps control the amount of protein that is produced. Keeping the cold of the RNA slows down the metabolism of the cell and stops the formation of the enzymes.
RNA structure: DNA has a strong spinal structure made up of two DNAs woven into a double helix. NRNAs are one mobile strands that sometimes attach to themselves and form neural shapes or secondary structures. These structures make some RNA more fragile than others.
Thermal Packing
To keep its vaccine cool and viable during shipping and short-term storage, Pfizer developed a thermal conductor, or “cool box”. ”It’s about the size of a suitcase. These boxes can keep the vaccine stable at −94 ° F ± 14 ° F (−70 ° C ± 10 ° C) for long periods of time using dry ice. The boxes are said to maintain that temperature for 10 days unopened allowing airlines and trucks to be distributed worldwide. Once open, health care workers can use the boxes as temporary storage for up to 30 days if they are refilled with dry ice every five days.
If the ice is dry in the boxes, they must be poisoned to stop the buildup of CO2 gas because dry ice moves directly to gas. It can lift weights and back pack if not released. Ice cream is also a danger to workers who load and unload it, as it can suffocate if CO2 gas is picked up in an enclosed space, without pollution.
Each cool box contains a GPS-enabled sensor that tracks its position and temperature. After dissolving the vaccine filters, they can be safely stored for up to five days at 35 ° F to 46 ° F).
Pfizer cool boxes also need batteries that withstand the frigid temperature. One company, Tadiran, manufactures specially modified lithium batteries (lithium thionyl chloride, LiSOCl2) for use in the cold chain for temperatures down to −112 ° F. These bobbin type batteries can be charged. used in wireless sensors to continuously monitor the behavior of foods, medicines, vaccines and frozen or packaged tissue samples in dry ice.
They feature a non-aqueous electrolyte converted to Arctic temperature and generate 3.6 V. They have twice the energy density of other lithium battery chemicals and have a service life of 20+ years. The batteries have a glass-to-metal hermetic seal rather than the more common crimped elastomer gasket as the seal better prevents battery leakage.
Tadiran certified and UL recognized cold chain lithium batteries are available in 1 / 2AA, 2 / 3AA, AA, C, D and DD cylinder cells; wafer cell; and standard battery packs. In addition, Tadiran manufactures a full line of 40-year LiSOCl2 batteries, including cylinder packs, dog size and battery.
Logistics
Based on projections, Pfizer, working with BioNTech, could deliver up to 50 million vaccine doses in 2020 and will deliver over 1.3 billion doses by the end of 2021 (subject to manufacturing capacity and licensing regulatory or consent).
Pfizer uses five of its facilities to make the vaccines: They are located in St. Louis; Andover, Mass .; Kalamazoo, Mich .; Pleasant Prairie, Wisc .; and Puurs, Belgium.
The federal government last week announced a contract for 100 million doses of Moderna vaccine for $ 1.5 billion and is said to maintain a contract for an additional 100 million. one billion. Moderna is charging $ 32 to $ 37 per dose for some customers with larger size purchases eligible for lower prices.
Apparently the hardest part of the challenge is not relying on engineering: injecting those millions of doses into people across the U.S. and the world and then making sure they get two doses. Concerns about the problem are those who refuse to get vaccinated for themselves or their children. This could promote crimp for herd immunity.
For more information
● The first wave of vaccine distribution.
● Background information on the cold chain circulation network.
● The president of the National Academy of Engineering discusses how engineers are dealing with the COVID Emergency.