Fourth dose, Moderna’s bivalent anti-Covid vaccines as possible candidates for the autumn booster

If everyone has to undergo a new dose of Covid vaccine in the fall, it may be with a product bivalent. One of these could be a booster that the US Moderna is developing. One of these has just arrived in phase 2 clinical trials. In a press release, the group announced the first results of this combination – dubbed mRna-1273.211 – which combines the already approved vaccine with the addition of messenger Rna that encodes the Spike protein of the strain Beta of the coronavirus. The test revolves around two different dosages (50 and 100 micrograms total). Along with the release, there is also a pre-print survey of the data, which is a step up from the way pharmaceutical groups have disseminated the results in recent years.

In the trial, the company’s scientists compared the effectiveness of a traditional booster dose versus one performed with the new product on 300 and 500 people, measuring the antibody titer for different strains of coronavirus at 28 and 180 days after injection. The result is that the booster – what for many would be the fourth dose – it would seem more effective with the new product than with the old one, even against the so-called “wild-type” initial strain from Wuhan (Wuhan-Hu-1). In other words, two mRNAs encoding two different Spike proteins would seem to favor a broader umbrella response, as other investigations had suggested. Same effect against Beta, Delta and especially Omicron strainswhich is obviously the lineage that interests us most.

And if from the point of view of safety there seems to be nothing to report, the fact remains that the study appears too limited in size in particular to highlight any rare side effects and perhaps related to the specific variant. As pointed out by many, for example on the Sheet, then there are other questions to ask: for example why to propose in the autumn a bivalent based on Delta and not on the more recent Omicron (which, however, is under development and necessarily late because the variant emerged after Beta). Another aspect: Moderna trial 2 for this bivalent appeal it actually consists of a third dose, and not in a fourth. But in Italy we are already at a good point with the recalls. What kind of information does an experimental path of this kind provide us with?

There is an answer to these questions. Moderna is actually testing different bivalent products which, just like mRna-1273.211, combine the mRna encoding the Spike protein of the original vaccine with the mRna encoding the Omicron variant. In this case, for the product mRna-1273.214, the first data are expected for the second quarter of the year. But the group is also experimenting with other monovalent boosters, i.e. vaccines similar to the previous ones but designed only on the Spike of the main Omicron strain. But what seems to be at the most advanced stage is precisely the bivalent designed on the Wuhan and Beta strains. Moderna’s Chief Executive Officer Stéphane Bancel has set the record straight by explaining that the bivalent booster they are aiming for for the fall is mRNA-1273.214, which combines “the current licensed vaccine with the booster candidate for Omicron”.

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