The FDA, on Jun 30, recommended that COVID-19 vaccine manufacturers develop bivalent (or two-component) COVID-19 booster vaccines, which will target the newer Omicron subvariants, namely BA.4 and BA.5.
The FDA recommendation is based on the recently convened Vaccines and Related Biological Products Advisory Committee (VRBPAC) meeting held earlier this week that voted in favor of including a component of the Omicron variant in the COVID-19 booster vaccines for use later this year.
As a result of this new recommendation, vaccine makers like Pfizer PFE/BioNTech BNTX and Moderna MRNA would be required to modify the design of their respective vaccine boosters to target the Omicron BA.4 and BA.5 subvariants.
The FDA expects to start administering these new vaccines later this year during the early to mid-fall season. However, the vaccine makers are expected to start clinical studies on these vaccines and submit the requisite data to the FDA for evaluation before securing authorization for using them.
Currently, BA.4 and BA.5 are the dominating Omicron subvariants, which are responsible for more than half of all COVID-19 cases in the United States. Moreover, these two subvariants outcompete the BA.1 Omicron subvariant and have shown the potential to evade immune protection. This creates a need for adapted vaccine boosters with improved vaccine effectiveness.
For the time being, the FDA has also asked vaccine makers not to change their vaccines for primary vaccination, as the administration of a primary regimen provides a base for protection against serious outcomes (hospitalization and death) caused by the circulating COVID-19 strains.
Though the administration of a primary vaccination regimen has helped reduce serious outcomes caused by COVID-19 variants, clinical studies have shown the antibody levels to wane over time. While authorized booster doses have restored these antibodies to their previous levels, this protection also weakens over time. As a result, there is a huge need for booster doses, which provide protection against the new emerging variants and thereby prevent serious outcomes caused by the disease.
The currently authorized/approved vaccines being marketed by Pfizer with partner BioNTech and Moderna and their currently available boosters are designed to target the ancestral coronavirus strain that emerged in late 2019. However, Pfizer/BioNTech and Moderna are developing Omicron-based COVID-19 vaccine boosters to address the rise of new and evolving Omicron subvariants. These Omicron-targeted vaccines have shown promise in clinical studies.
Last month, both Pfizer/BioNTech and Moderna announced positive data from their respective clinical studies, which are evaluating their respective Omicron-specific vaccine candidates. Data from these studies have already been reported to the FDA.
Moderna announced data from an ongoing phase II/III study on its bivalent COVID-19 vaccine booster candidate, mRNA-1273.214, targeting the Omicron variant. The clinical data showed that following one month of administration of a 50 µg dose of mRNA-1273.214, a 5.4-fold increase in neutralizing antibodies against the Omicron subvariants BA.4 and BA.5 was seen in all study participants, regardless of prior infection. In a subset of seronegative participants, the candidate generated a 6.3-fold increase in neutralizing titers against both the Omicron subvariants.
Pfizer and BioNTech are also working on new Omicron-based vaccine candidates, both monovalent and bivalent, in a phase II/III study. The bivalent vaccine is a combination of the ancestral strain and the Omicron BA.1 subvariant. Last month, both the companies announced data from this study, which showed that participants, given the booster dose of both the vaccine candidates, generated a substantially higher immune response against the Omicron subvariant BA.1compared to Comirnaty, Pfizer/BioNTech’s currently authorized vaccine.
Though Pfizer and BioNTech’s monovalent and bivalent vaccine candidates have efficiently neutralized both the subvariants, based on data from the preliminary laboratory studies, the neutralizing titers generated on dosing with both the vaccine candidates were three-fold lower than the neutralizing titers against the BA.1 variant.
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