General questions

What are the so-called COVID-19 bivalent booster vaccines?


Some of the existing mRNA COVID-19 vaccines have been adapted to better match the circulating variants of SARS-CoV-2. The updated vaccines contain two messenger RNA molecules: one with instructions for producing a protein from the original strain of SARS-CoV-2; and the other one - either a molecule with instructions for producing a protein from the Omicron BA.1 subvariant or a molecule with instructions for producing a protein from the Omicron BA.4 and BA.5 subvariants of SARS-CoV-2.

These updated vaccines can broaden protection against different variants and are therefore expected to help maintain optimal protection against COVID-19 as the virus evolves.

The European Medicines Agency’s human medicines committee (CHMP) has recommended since 1 September 2022 to authorize the three following bivalent vaccines adapted to provide broader protection against COVID-19:

  • Pfizer’s Comirnaty Original/Omicron BA.1
  • Spikevax bivalent Original/Omicron BA.1 and
  • Pfizer-BioNTech’s Comirnaty Original/Omicron BA.4-5.

The bi-valent vaccines are intended for use as booster doses in people aged 12 years and above who have received at least primary vaccination against COVID-19. These adapted versions of the original vaccines Comirnaty (Pfizer-BioNTech) and Spikevax (formerly Moderna) can trigger strong immune responses against Omicron BA.1 and the original SARS-CoV-2 strain in people previously vaccinated. In particular, they were more effective at triggering immune responses against the BA.1 subvariant than the original vaccines. Side effects observed with the adapted vaccines were comparable to those seen with the original ones and were typically mild and short-lived.

The BA4-BA5-containing bivalent vaccines were approved to maximize protection against currently circulating Omicron variant lineages based on the totality of available evidence, including:

  • extensive safety and effectiveness data for each of the monovalent mRNA COVID-19 vaccines,
  • safety and immunogenicity data obtained from a clinical study of a bivalent COVID-19 vaccine that contained mRNA from Omicron variant BA.1 lineage, and
  • nonclinical data obtained using a bivalent COVID-19 vaccine that contained mRNA of the original strain and mRNA in common between the BA.4 and BA.5 lineages of the Omicron variant.

Similarly, the US Food and Drug Administration amended the emergency use authorizations of the Moderna COVID-19 vaccine and the Pfizer-BioNTech COVID-19 vaccine to authorize bivalent formulations of the vaccines (Moderna COVID-19 Vaccine, Bivalent (Original and Omicron BA.4/BA.5) and Pfizer-BioNTech COVID-19 vaccine, bivalent (original and Omicron BA.4/BA.5)) for use as a single booster dose following primary or booster vaccination.

As the pandemic evolves, the strategy is to have a broad range of adapted vaccines that target different SARS-CoV-2 variants so countries have a plurality of options to meet their needs when they design their vaccination strategies. This is a key element in the overall strategy to combat the pandemic as it is not possible to predict how the virus will evolve in the future and which variants will be circulating this winter.

The original vaccines, Comirnaty and Spikevax (formerly Moderna), are still effective at preventing severe disease, hospitalization and death associated with COVID-19 and will continue to be used within vaccination campaigns in the EU, in particular for primary vaccinations.


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