FDA approves new Covid-19 booster, targeting XBB.1.5

In the ongoing effort to mitigate the effects of Covid-19, the US Food and Drug Administration approved new Covid-19 vaccines for emergency use. Additionally, the Centers for Disease Control and Prevention recommended these new boosters for everyone over 6 months old. These new formulations are better suited to the strains of the virus currently circulating. And like previously approved vaccines, they are expected to reduce the rate of serious illness, hospitalizations and deaths among people infected with SARS-CoV-2, the virus that causes Covid-19.

The new vaccines, developed by Moderna and Pfizer-BioNTech, use the same mRNA-based technology as previously approved versions of their vaccines. However, the mRNA itself has been modified to reflect the change in the virus. These latest vaccines contain mRNA encoding the spike protein of the omicron subvariant XBB.1.5. Preliminary data shows that this booster will trigger the production of antibodies that recognize this form of SARS-CoV-2. This reinforcement may also provide enhanced protection against other circulating subvariants.

As we have seen throughout the pandemic, the virus evolves over time. The first Covid-19 vaccines, approved for use in December 2020, contained a segment of mRNA that encoded the spike protein of the original SARS-CoV-2 virus. However, over time, viral variants emerged that contained mutations in the gene that encodes the spike protein. These mutations negatively affected the effectiveness of the original vaccines and led drug manufacturers to develop new formulations to better target the new viral strains.

In response to the increase in Covid-19 cases associated with the omicron variant, for example, Moderna and Pfizer-BioNTech converted their vaccines from monovalent to bivalent. Approved for use in August 2022., these boosters contained two mRNA fragments, one encoding the spike protein of the original virus and another encoding the spike protein of the omicron subvariants BA.4 and BA.5, which were dominant worldwide at the time. . on time. However, by late 2022, the prevalence of these subvariants had decreased and a new omicron subvariant, XBB.1.5, emerged. The prevalence of this subvariant increased rapidly, prompting the development of the latest Covid-19 vaccine formulations.

But XBB.1.5 is no longer the dominant variant. In May 2023, XBB.1.5 accounted for about half of all Covid-19 infections in the US. By July, that figure had dropped to less than a quarter. Today, XBB.1.5 accounts for less than 5% of infections. During this time, the prevalence of another omicron subvariant, EG.5, has been increasing. This variant now accounts for approximately 25% of all infections.

And researchers are eagerly monitoring yet another subvariant, BA.2.86. Also known as Pirola, this subvariant was first detected in Denmark in July 2023. Since then, it has been detected in 15 countries, including the United States, according to the international virus tracking site GISAID. Until now, the prevalence of this variant has remained low. But scientists remain concerned about the large number of mutations it has, especially in the spike protein gene. Some researchers worry that this constellation of changes could allow this variant to evade existing vaccines and be more transmissible than its predecessors.

So is the XBB.1.5 vaccine already obsolete? No. In a press release published on September 6, 2023, Moderna announced that trial participants who received their XBB.1.5-based vaccine produced neutralizing antibodies against EG.5 and BA.2.86. In other words, this new vaccine results in the production of antibodies that recognize the currently dominant subvariant and a potentially concerning subvariant. Furthermore, in a manuscript currently under peer review, researchers from Harvard University and Los Alamos National Laboratories report that, despite its numerous mutations, BA.2.86 may not be as capable of evading immunity as originally feared.

This new vaccine will undoubtedly provide better protection than existing vaccines against the Covid-19 strains currently circulating. But what comes next? The virus will continue to evolve. That is sure. So, for the foreseeable future, we can probably expect updated vaccines against Covid-19 to be released periodically, in response to new variants. However, maybe that will change. Researchers from various institutions, such as Duke Human Vaccine Institute, are actively trying to develop a pan-coronavirus vaccine, a vaccine that can effectively inhibit multiple different coronaviruses. However, until that goal becomes a reality, we may be trapped in a perpetual game of cat and mouse.

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