Moderna reports promising data on booster shot efficacy

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The company said vaccinated people who received a single 50-microgram dose saw a rapid increase in antibodies

On Wednesday, Moderna said its booster doses appear to be effective in reinvigorating the immune system’s response to COVID-19 and its variants. The vaccine maker said a booster shot delivering a half-dose of its vaccine (50-micrograms) bolstered the immune response to both the B.1.351 and P.1 variants, as well as the original COVID-19. 

Company officials said data from the ongoing Phase 2 trial showed that half of the previously vaccinated participants had generated a low antibody response against the B.1.351 and the P.1 variants (the South African and Brazilian variants, respectively) before they got the booster shot. But two weeks after they received the booster dose, their antibody levels had increased. 

“The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of mRNA-1273 to induce immune memory,” said Moderna CEO Stéphane Bancel. “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.” 

As far as side effects go, Moderna said the “majority of adverse events were mild or moderate in severity.” Commonly cited side effects included pain at the injection site, fatigue, and headache, as well as muscle and joint pain.

Promising trial results

Moderna is currently testing three different methods to boost the immune response to the virus and its variants. The first approach would be to “strain-match” the booster shots by specifically targeting each variant with a specially formulated booster shot, but at a lower dose than the original vaccine. Moderna is also evaluating the potential of combining the original vaccine with a variant-specific vaccine into one shot (50-micrograms or lower). Finally, the company is testing a third shot of the initial vaccine at a lower dosage. 

Moderna explained that its vaccine is built on mRNA technology, which enables scientists to tweak the genetic code in a way that helps the body learn how to produce antibodies to fend off a specific virus. 

“As we seek to defeat the ongoing pandemic, we remain committed to being proactive as the virus evolves,” Bancel said. “We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants.”

Moderna said the preliminary results of its most recent trial will soon be published online. They have not yet been peer-reviewed. 

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