Moderna said that a single booster dose of its original COVID-19 vaccine — or a modified version made specifically for the variant first identified in South Africa — offered protection against two SARS-CoV-2 variants of concern.

Preliminary phase 2 trial results demonstrated that both vaccines increased neutralizing titers against wild-type SARS-CoV-2 and the two variants — B.1.351 and P.1, which was first identified in Brazil — in previously vaccinated patients, Moderna said.

“We are encouraged by these new data, which reinforce our confidence that our booster strategy should be protective against these newly detected variants. The strong and rapid boost in titers to levels above primary vaccination also clearly demonstrates the ability of mRNA-1273” — the original vaccine — “to induce immune memory,” Moderna CEO Stéphane Bancel, MSc, MBA, said in a press release.

Moderna is testing three booster options for improving neutralizing titers in previously vaccinated people — mRNA-1273.351, a vaccine based on the B.1.351 variant; mRNA-1273.211, a multivalent booster that contains a mix of mRNA-1273 and mRNA-1273.351 in a single dose; and a 50 µg booster dose of mRNA-1273.

Researchers analyzed participants in the phase 2 trial for the presence of pseudovirus neutralization titers before boosting 6 to 8 months after their primary vaccination. Although 37 of 40 participants had titers for wild-type SARS-CoV-2, titers for the B.1.351 and P.1 variants were significantly lower, with only half of participants having titers less than the assay limit before boosting, Moderna reported.

The company said all participants experienced boosted titers to all variants 2 weeks after receiving a single dose of either mRNA-1273 or mRNA-1273.351. The mRNA-1273.351 booster appeared more effective at increasing neutralization titers than mRNA-1273, with higher average geometric mean titer (GMT) levels at 15 days after administration of the booster dose (GMT = 1,400 vs. GMT = 864, respectively).

Safety and tolerability of both boosters were comparable to the second dose of mRNA-1273.

Moderna said the preliminary results have been submitted to the preprint server bioRxiv and will be submitted for peer review once the arm testing a booster dose with mRNA-1273.211 is complete.

Moderna is also currently testing its mRNA vaccine in children aged 6 months to 12 years. Multiple real-world studies have shown that the vaccine — and another messenger RNA vaccine developed by Pfizer and BioNTech — are highly effective against COVID-19.