COVID-19 Vaccine Booster Dose Increases Immune Response to SARS-CoV-2, 2 Variants

Moderna announced a single 50 µg dose of its mRNA-1273 or mRNA-1273.351 vaccine given as a booster to previously vaccinated individuals increased neutralizing antibody titer responses against SARS-CoV-2, B.1.351 (South Africa) and P.1 (Brazil) variants.

This finding come from its phase 2 study. In addition, its mRNA-1273.351 booster dose, which is Moderna’s strain-matched booster, showed higher neutralizing antibody titers against the B.1.351 variant than a booster dose of mRNA-1273.

“We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants," said Stéphane Bancel, Chief Executive Officer of Moderna. "The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of mRNA-1273 to induce immune memory.”

With the mRNA-1273.351 booster dose, investigators reported it was more effective at increasing neutralization titers against the B.1.351 variant when compared to mRNA-1273, as evidenced by higher mean GMT levels already at 15 days following booster dose (GMT = 1400 for mRNA-1273.351; GMT = 864 for mRNA-1273).

The relative decrease in neutralizing titers between the wild-type (D614G) and B.1.351 assays also improved with mRNA-1273.351 booster, from a 7.7-fold difference prior to boost to a 2.6-fold difference 15 days after boost, suggesting a potentially more balanced immune response against the tested variants.

This news is welcoming as the world is racing to vaccinate people in the midst of the emerging variants, which have shown to be more contagious and up until now that the current crop of authorized and investigational COVID-19 vaccines have demonstrated a lowered effectiveness against the B.1.351 variant.

Participants in the Moderna study were tested for pseudovirus neutralization (PsVN) titers prior to boosting approximately 6 to 8 months after their primary vaccination series. Although titers versus the wild-type SARS-CoV-2 virus remained high, with 37 of 40 participants having detectable titers, titers against the variants of concern (B.1.351 and P.1) were much lower, with approximately half of participants having titers below the assay limit of quantification prior to boosting. Two weeks after receiving either mRNA-1273 or mRNA-1273.351, PsVN titers were boosted in all participants and all variants tested.

This comes as vaccine developers have considered pivoting to address the variants in order to stay ahead of them and remain effective.

Moderna believes its vaccine platform allows it the ability to address the variants as well as other diseases.

“Our mRNA platform allows for rapid design of vaccine candidates that incorporate key virus mutations, potentially allowing for faster development of future alternative variant-matched vaccines,” Bancel said.

In a study reported earlier this week, the P.1 variant was reported to be 1.7 to 2.4 times more transmissible and can evade 10% to 46% of gained immunity.

“Our epidemiological model indicates that P.1 is likely to be more transmissible than previous strains of coronavirus and likely to be able to evade immunity gained from infection with other strains,” Samir Bhatt, a corresponding author on the study, said.

In addition, Moderna plans on releasing data soon on its mRNA-1273.21 candidate, which is a multivalent booster, that combines mRNA-1273 and mRNA-1273.351 into a single vaccine, as well as data on a lower dose of mRNA-1273.351.