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Third mRNA Vaccine Copies Itself, Shows 55% Efficacy

Sandipan Talukdar |
The vaccine repeatedly produces the mRNA strand in the body and stays for a much longer period inside the cell.

After the mRNA vaccines manufactured by Moderna and Pfizer-BioNTech, a similar vaccine has been developed by Arcturus Therapeutics, San Diego. During the placebo-controlled trial on April 20, the developer announced that the vaccine has considerable efficacy.

The trial involved 17,000 participants in Vietnam and the company claimed that the vaccine has 55% efficacy against symptomatic COVID-19 patients and 95% against severe illness and death. The developer also claimed that the vaccine may provide significant advantages like easier storage and lower cost in comparison to the vaxes of Moderna and Pfizer-BioNTech. Moreover, the vaccine is a self-amplifying mRNA and requires smaller doses.

Arcturus’s vaccine contains mRNA that elicits an immune response against the virus. The mRNA is from the coronavirus and makes a protein of it against which our immune system gets trained. In case of subsequent exposure to the virus, the immune system unleashes a robust attack to minimise the impact. 

The vaccine applies a process of freeze-drying where the mRNA-filled solution is transformed into a powder which can be stored at room temperature. It can be hydrated later for use in injections. The benefit of it in real terms is that it does not require extreme cold storage. Vinbiocare Biotechnology, the partner of Arcturus which carried the trial in the country, reportedly said that it can manufacture the vaccine by itself. On the other hand, the mRNA vaccines of Pfizer-BioNTech and Moderna lack this provision and require cold storage of as much as -80 degrees Celsius. 

Arcturus’s vaccine is also self-amplifying, meaning it can repeatedly produce the mRNA strand in the body and thus can stay for a much longer period inside the cell. For this purpose, Arcturus and other vaccine manufacturers that are in the process of bringing out self-amplifying vaccines have enzymes from other viruses to cause the mRNA to be produced repeatedly. 

Deborah Fuller, a vaccinologist at Washington University School of Medicine who is also involved in the production of self-amplifying mRNA vaccines, said, “It’s a huge accomplishment that for the first time a self-amplifying RNA vaccine has been shown to be safe and effective.”

A self-amplifying mRNA COVID-19 vaccine ideally would replace the two primary doses, giving it an even clearer benefit over its conventional relatives, Fuller added. “A booster months later might still be warranted as is encouraged now for the current mRNA vaccines. But self-amplifying mRNAs also could lead to more durable immune responses.”

Under the trial, which began last August, two doses each containing 5 micrograms of the self-amplifying mRNA were administered within a gap of 28 days. The Pfizer-BioNTech and the Moderna vaccines too were administered in two doses but contained 30 and 100 micrograms of the mRNA respectively.

Notably, the Arcturus vaccine showed an efficacy of 55% against symptomatic infections whereas the previous mRNA vaccines showed 90%-95% efficacy in their trials. However, the previous vaccines countered the original SARS-CoV-2 strains and the Arcturus is pitted against the Delta and Omicron variants, which had overwhelmed Vietnam during the trial period. During Arcturus’s trial, out of the 43 severe cases, only 10 were found to be vaccinated and 9 out of 10 deceased got the placebo. The manufacturer aims to launch another trial involving 2,400 people for the efficacy of a booster dose.

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