Two of Moderna’s COVID-19 vaccine booster shots under study induced an immune response against SARS-CoV-2 and variants first identified in South Africa and Brazil, the company announced Wednesday. A variant-specific booster shot resulted in higher levels of neutralizing antibodies against the concerning South African variant with fewer side effects than a third shot of the original vaccine.
The early findings stem from a Phase 2 trial, administering a 50 µg dose of mRNA-1273 or the variant-specific shot, mRNA-1273.351, given as a booster to previously vaccinated individuals. Another vaccine under study involves a "50-50 mix" of the previously authorized vaccine and the variant-specific booster shot in a single vaccine.
"As we seek to defeat the ongoing pandemic, we remain committed to being proactive as the virus evolves. 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, CEO of Moderna, in a statement posted Wednesday.
"The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of mRNA-1273 to induce immune memory," Bancel continued. "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 should they be needed."
The early findings announced Wednesday included data two weeks post-vaccination with the booster shot, the company said. Further findings, which Moderna said are "expected shortly," will involve more samples gathered at later time periods post-booster shot, findings on the 50-50 combination vaccine, as well as a lower dose of the variant-specific shot.
Moderna said that study participants had high levels of protection against the original strain up to eight months after completing the initial two-dose regimen, but levels of antibodies against strains first detected in South Africa and Brazil "were much lower." Two weeks after the booster shot, antibody levels ramped up to levels on par or higher than the previously reported levels against the original strain.
Moderna specifically noted a 7.7-fold difference in antibody levels between the original strain and South African variant before the shot, and a 2.6-fold difference 15 days following the variant-specific booster shot.
The early findings also suggested the booster shots were safe and are "generally comparable" with the previously authorized two-dose series.
"A review of solicited adverse events indicated that the vaccine boosters were generally well-tolerated," the company statement reads. "The majority of adverse events were mild or moderate in severity."
The most common side effects after the booster shots were fatigue, headache, myalgia and arthralgia.