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When you go to a supermarket and want to buy 10 bottles of whole milk for your children, you usually assume the chemicals and concentrations in these 10 bottles are the same or similar. No one would expect five of the bottles to be filled with watered-down milk while the other five were filled with yogurt.

Most store-bought foods meet our expectations because of regulations and quality control. The same criteria also exist in the pharma industry, including vaccine products.

We expect consistent physical and chemical parameters of key ingredients across different batches of drug or vaccine products. Consistency is the foundation that allows patients and consumers to have confidence in the safety and effectiveness of medications.

The CMC process—short for chemistry, manufacturing, and controls—involves defining manufacturing practices and product specifications that must be followed to ensure product safety and consistency between batches. This is a mandatory criterion for global health authorities to approve a drug or vaccine.

Controlling the quality of a traditional chemical product is relatively straightforward, but for a biological product, like an mRNA, things become more complicated.

Our DNA contains gene codes composed of nucleotides. DNA makes proteins consisting of amino acids. Between the gene code and protein, there is a bridge molecule, a “translator”—called messenger RNA (mRNA).

The full-length mRNA sequence of the Pfizer vaccine coding for the spike protein is 4,284 nucleotides in length.

It consists of a 5′ CAP structure to prime its translation into a spike protein. It works like an ignition box of a car. At the end of the translatable region, the open reading frame, there is a stop codon, which is like a car’s brakes. If a truncated mRNA does not contain a stop codon, it fails to give a “brake” signal. The protein translation process will continue endlessly.