Moderna Booster Shot Bolsters Antibodies Against Variant Strains

(Bloomberg) -- Moderna Inc.’s Covid-19 booster shots gave positive results against immune system-evading strains that emerged in South Africa and Brazil, according to early results from a mid-stage trial.

Two types of booster shots studied spurred higher levels of virus-halting antibodies against the variant strain P.1 that ravaged Brazil as well as B.1.351, common in South Africa, Moderna said in a statement. One of the boosters is an additional low-dose shot of its existing vaccine, while the other type is customized against the South Africa strain.

Scientists and drugmakers are moving rapidly to head off the rise of coronavirus variants with new mutations that may help them elude existing vaccines from Moderna, partners Pfizer Inc. and BioNTech SE, and Johnson & Johnson. South Africa halted its rollout of AstraZeneca Plc’s vaccine after a study showed limited effectiveness against the variant circulating there.

In Moderna’s trial, the customized booster, called mRNA-1273.351, produced the highest levels of antibodies against the strain common in South Africa. The initial results are based on Covid antibody levels two weeks after the booster shots, and the trial is continuing to gather more data, Moderna said. The trial is also examining a third type of booster that combines equal amounts of the existing vaccine with the customized booster mRNA-1273.351.

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“We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants,” Stephane Bancel, Moderna’s chief executive officer, said in a statement. “We will continue to make as many updates to our Covid-19 vaccine as necessary to control the pandemic.”

Moderna submitted a manuscript detailing the early results to the preprint site bioRxiv, the company said. It plans to submit trial data for formal publication once it has results from the third arm of the study.

The boosters were generally well tolerated with some side effects comparable to those seen after the second dose of its existing Covid-19 vaccine, including fatigue, headache, and pain in muscles, joints and at the injection site, Moderna said.

Moderna, Pfizer and other vaccine makers are racing to develop booster shots against emerging variant strains. It’s not yet clear when or if these boosters will be needed, or who would get them if they are. But the companies are preparing for a scenario where the virus keeps mutating and periodic booster shots may be required.

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