A durable mRNA vaccine for COVID-19, which can be kept at fridge temperatures for at least three months, has just passed Phase I trials.
The two-dose vaccine, called ChulaCov19, was developed in Thailand with input from both Thai and international researchers.
The vaccine was made in North America for its first trials, but Thailand is preparing to make it at scale if it passes Phase II and III trials.
The Phase I trial, done on a group of 72 adults, has shown that the vaccine is safe , has mild side effects, and triggers COVID-19 antibodies.
The results of the trial are published in Nature Microbiology.
The currently-used Pfizer and Moderna mRNA vaccines can only be stored at fridge temperatures (2°C – 8°C) for 10 weeks and 30 days, respectively.
Longer than that, and they need temperatures well below zero: at least -15°C for Moderna, and -60°C for Pfizer. This makes them expensive to store and transport, meaning the vaccines are difficult to use in low- and middle-income countries.
Non-mRNA COVID vaccines, like Novavax and AstraZeneca, can be kept in fridges for longer.
“Among approved vaccines, mRNA vaccines have the highest efficacy,” point out the researchers in their paper.
“Building capacity to develop and manufacture mRNA vaccines in low- to middle-income countries is important for the current and future pandemics.”
ChulaCov19 uses the same basic structure as the Pfizer and Moderna vaccines: mRNA, which the body uses to make COVID-19 spike proteins, coated in fatty capsules called lipid nanoparticles.
The researchers state that their vaccine is different from Pfizer’s and Moderna’s in two ways.
First, they use different lipids to make the nanoparticle capsules that encase the mRNA. (For more on mRNA vaccine ingredients, read our explainer.)
Second, ChulaCov19 isn’t “prefusion stabilised”: this is a property that helps the spike proteins, once formed in the human body, to properly take shape.
Despite lacking this stabilisation, lab tests on participants’ blood showed that the highest dose of ChulaCov19 (50 micrograms) produced more antibodies than the Pfizer vaccine.
While it neutralised the Alpha, Beta, Gamma and Delta variants of SARS-CoV-2 with similar efficacy, the vaccine produced fewer effective antibodies against the Omicron variant of the vaccine. (It was first developed before any of these variants arose.)
Side effects from the trial were largely mild. Most trial participants reported pain at the injection site, while some reported fevers, chills, headaches, joint pain or stiffness, and fatigue. This was more common after the second dose.
ChulaCov19 is now in Phase II clinical trials, where it’s being tested on a larger group of people to see if it works at preventing either infection with, or serious symptoms from, COVID-19.
If these results are favourable, the vaccine will then go through Phase III clinical trials to see if it works in a big cohort.
According to the World Health Organization’s tracker, there are currently 172 COVID-19 vaccines in the clinical phase of development.
Of these, 40 are RNA-based: the second most common type of vaccine in trials. The most common, at 55, is protein subunit vaccines, like the Novavax vaccine.
Ellen Phiddian is a science journalist at Cosmos. She has a BSc (Honours) in chemistry and science communication, and an MSc in science communication, both from the Australian National University.
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