Moderna Covid-19 booster shot bolsters antibodies against variant strains

Early results from trial show Moderna's booster shot helps against variants of concern found in Brazil and South Africa

A pharmacist prepares a dose of the Moderna Covid-19 vaccine in Washington, DC, on April 27, 2021. Bloomberg

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

Two types of booster shots studied spurred higher levels of virus-halting antibodies against the variant strain P1 that ravaged Brazil and B1351, common in South Africa, Moderna said.

One of the boosters is an additional low-dose shot of its existing vaccine, while the other is customised against the South Africa strain.

Scientists and drug makers are moving rapidly to head off the rise of variants with new mutations that may help them to elude existing vaccines from Moderna, partners Pfizer and BioNTech, and Johnson & Johnson.

South Africa halted its use of AstraZeneca’s vaccine after a study showed limited effectiveness against the variant circulating there.

In Moderna’s trial, the customised 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-19 antibody levels two weeks after the booster shots, and the trial is continuing to gather data, Moderna said.

It is also examining a third type of booster that combines equal amounts of the existing vaccine with the customised booster.

“We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants,” said Stephane Bancel, Moderna’s chief executive.

“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 and headaches, 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 the emerging variant strains.

It is 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 siuation where the virus keeps mutating and periodic booster shots may be required.