Understanding messenger RNA and other SARS-CoV-2 vaccines


Early efficacy results have been surprising

Both vaccines were reported to produce about 95% efficacy in the final analysis. That was unexpectedly high because most vaccines for respiratory illness achieve efficacy of 60%-80%, e.g., flu vaccines. However, the efficacy rate may drop as time goes by because stimulation of short-term immunity would be in the earliest reported results.

Dr. Michael E. Pichichero, a specialist in pediatric infectious diseases, and director of the Research Institute at Rochester (N.Y.) General Hospital

Dr. Michael E. Pichichero

Preventing SARS-CoV-2 cases is an important aspect of a coronavirus vaccine, but preventing severe illness is especially important considering that severe cases can result in prolonged intubation/artificial ventilation, prolonged disability and death. Pfizer/BioNTech had not released any data on the breakdown of severe cases as this column was finalized. In Moderna’s clinical trial, a secondary endpoint analyzed severe cases of COVID-19 and included 30 severe cases (as defined in the study protocol) in this analysis. All 30 cases occurred in the placebo group and none in the mRNA-1273–vaccinated group. In the Pfizer/BioNTech trial there were too few cases of severe illness to calculate efficacy.

Duration of immunity and need to revaccinate after initial primary vaccination are unknowns. Study of induction of B- and T-cell memory and levels of long-term protection have not been reported thus far.

Could mRNA COVID-19 vaccines be dangerous in the long term?

These will be the first-ever mRNA vaccines brought to market for humans. In order to receive Food and Drug Administration approval, the companies had to prove there were no immediate or short-term negative adverse effects from the vaccines. The companies reported that their independent data-monitoring committees hadn’t “reported any serious safety concerns.” However, fairly significant local reactions at the site of injection, fever, malaise, and fatigue occur with modest frequency following vaccinations with these products, reportedly in 10%-15% of vaccinees. Overall, the immediate reaction profile appears to be more severe than what occurs following seasonal influenza vaccination. When mass inoculations with these completely new and revolutionary vaccines begins, we will know virtually nothing about their long-term side effects. The possibility of systemic inflammatory responses that could lead to autoimmune conditions, persistence of the induced immunogen expression, development of autoreactive antibodies, and toxic effects of delivery components have been raised as theoretical concerns.4-6 None of these theoretical risks have been observed to date and postmarketing phase 4 safety monitoring studies are in place from the Centers for Disease Control and Prevention and the companies that produce the vaccines. This is a risk public health authorities are willing to take because the risk to benefit calculation strongly favors taking theoretical risks, compared with clear benefits in preventing severe illnesses and death.

What about availability?

Pfizer/BioNTech expects to be able to produce up to 50 million vaccine doses in 2020 and up to 1.3 billion doses in 2021. Moderna expects to produce 20 million doses by the end of 2020, and 500 million to 1 billion doses in 2021. Storage requirements are inherent to the composition of the vaccines with their differing lipid nanoparticle delivery systems. Pfizer/BioNTech’s BNT162b2 has to be stored and transported at –80° C, which requires specialized freezers, which most doctors’ offices and pharmacies are unlikely to have on site, or dry ice containers. Once the vaccine is thawed, it can only remain in the refrigerator for 24 hours. Moderna’s mRNA-1273 will be much easier to distribute. The vaccine is stable in a standard freezer at –20° C for up to 6 months, in a refrigerator for up to 30 days within that 6-month shelf life, and at room temperature for up to 12 hours.

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