Explained: How self-replicating mRNA Covid-19 vaccines work, and what trial results show – The Indian Express

A self-amplifying mRNA vaccine one in which the delivered RNA multiplies inside the body has shown promising results against Covid-19 in ongoing phase 1/2/3 trials. The vaccine, ARCT-154, has been developed by Arcturus Therapeutics Holdings, based in San Diego, California, and its trials are in progress in Vietnam. It offered 95% protection against severe Covid-19 and death, and 55% against Covid infection, Arcturus said in a press release.

WHAT IT MEANS: An mRNA vaccine, such as those from Pfizer/BioNTech and Moderna, use messenger RNA that encodes the spike protein of the coronavirus. In other words, the mRNA directs the cell to produce copies of the spike protein, so that the immune system will recognise the spike if and when actual infection takes place, and mount a response.

A self-amplifying mRNA vaccine is an improvement on the traditional RNA platform. It encodes four extra proteins in addition to the vaccine antigen, and these enable amplification of the original strand of RNA once inside the cell. The basic advantage is that it requires a smaller dose.

THE TRIAL: It enrolled over 19,000 adult subjects in Vietnam, including individuals at higher risk of severe complications of Covid-19 disease. The Phase 3 placebo-controlled vaccine efficacy portion of this study enrolled over 16,000 participants. An analysis between 7 days and 56 days after completion of a two-dose vaccination series demonstrated 55% vaccine efficacy for protection against Covid-19, the release said. These cases were detected during an outbreak in Vietnam when the Delta and Omicron variants were dominant.

The analysis of severe Covid-19 disease (including deaths) included 43 severe cases. Forty-one cases occurred in the placebo group and two in the vaccinated group, demonstrating vaccine efficacy of 95%, the release said. Nine deaths were reported in the placebo group, and one in the vaccinated group, whom the company described as an older age group participant who was also at increased risk of severe Covid-19.

ADVERSE EVENTS: The incidence of unsolicited adverse events in the two groups are comparable, the release said. No cases of myocarditis or pericarditis were reported; however, the company conceded that the study is not large enough to reliably observe these events given their extremely rare frequency of occurrence.

Adverse events collected in diaries of study participants (solicited adverse events) for seven days following each vaccination demonstrate that the majority of these events were mild or moderate in severity, it said. The majority of solicited adverse events resolved within the 7-day window of observation.

IMPLICATIONS: The Pfizer/BioNTech and Moderna vaccines against Covid-19 are the only two mRNA vaccines available so far. The new vaccine may come with significant advantages: easier storage, along with lower cost because its self-amplifying design allows for smaller doses, Science magazine said.

However, the magazine noted, much of the world has already been vaccinated, and the Arcturus vaccine may be making its debut too late, at least for primary vaccination.

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Explained: How self-replicating mRNA Covid-19 vaccines work, and what trial results show - The Indian Express