"We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants", Moderna CEO Stéphane Bancel said in a press release.
Before the volunteers got the third dose, Moderna tested blood samples to see how durable the vaccine response had been through six to eight months.
An updated vaccine tailored against the B.1.351 coronavirus variant worked best, the company said.
At least one vaccine dose for 70% of adults by July 4
But the struggle to break through many Americans' vaccine hesitancy is apparent in the less ambitious target that Biden announced. US officials are gearing up to administer vaccines to adolescents once that is approved by the Food and Drug Administration.
These are the first clinical results from any vaccine developer testing an updated COVID-19 shot.
To be clear, the results now haven't been peer-reviewed.
The volunteers received the booster shots about six to eight months after they had gotten the second dose of the original vaccine, as part of a mid-stage clinical trial that started a year ago.
Some volunteers received a 50-microgram dose of Moderna's authorized vaccine, half the usual dosage.
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I will work tirelessly with our Indian friends and partners in the public and private sector to fulfil our leaders' ambition. Last week the Prime Minister spoke to the CEOs of leading Indian technology firms and prominent investors Infosys and HCL.
The results show that while booster shots of either version of the vaccine increased antibodies against all of the variants of COVID-19 tested in the trial, the new booster had a bigger response against the South African variant than the original vaccine.
While no one knows exactly when people would need booster shots, experts generally think the presence of variants that can partially degrade the efficacy of vaccines will speed up the need to give additional shots, particularly to the most vulnerable populations. Moderna says the results have been submitted to pre-print server bioRxiv, but they're not yet online.
Neutralizing antibodies are proteins produced by the immune system that are custom-made to bind to a specific structure of a microbe. "The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of mRNA-1273 to induce immune memory".
The B.1.351 booster shot appeared to produce slightly less severe reactions, Moderna said.
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The board is an independent, court-like entity for appealing content decisions on Facebook-owned platforms. The social network itself asked the independent body to review Trump's eviction from the online community.
Side effects from this first trial were similar to those reported by people getting the second dose of Moderna's original vaccine, including headache, muscle and joint pain, and fatigue.