Moderna Begins Clinical Trial for Omicron-Based Booster Dose

Source: Freepik

The first participant in the clinical trial assessing an Omicron-specific Moderna booster shot has already received a dose.

Following the result of its phase 1 trial, Moderna has announced the commencement of its Phase 2 clinical trial for an Omicron-specific booster dose. The news comes just a day after Pfizer began recruiting participants for a trial assessing its Omicron-specific vaccine candidate. Results of Moderna’s phase 1 trial are available in the New England Journal of Medicine.

According to Moderna’s press release, the phase 2 trials will assess the safety and efficacy of its Omicron-specific booster dose. Around 600 participants, part of two cohorts, will receive a single booster dose of the modified booster dose. The first cohort will include individuals who have previously received two doses of the Moderna COVID-19 vaccine (mRNA-1273), with the second dose being 6 months prior to enrollment. Participants who have received two doses of Moderna’s vaccine and a 50 µg booster dose (3 months prior) will then form the second cohort.

We are reassured by the antibody persistence against Omicron at six months after the currently authorized 50 µg booster of mRNA-1273. Nonetheless, given the long-term threat demonstrated by Omicron’s immune escape, we are advancing our Omicron-specific variant vaccine booster candidate and we are pleased to begin this part of our Phase 2 study.

Stéphane Bancel, Chief Executive Officer of Moderna

Antibodies Level Fall After 6 Months

In December of last year, Moderna released preliminary data on its standard booster dose’s efficacy against Omicron. As part of the trial, researchers had administered a standard 50 µg dosage and a higher dose of 100 µg. The results showed a 37-fold increase in antibody levels following the standard dosage. While the higher dosage caused an 83-fold higher antibody levels.

Wednesday’s data includes results from a trial involving samples from participants who had either received the standard booster or Moderna’s other bivalent candidates. However, none of them targeted the Omicron variant specifically. The researchers conducted laboratory tests using samples from individuals who had received two doses of the Moderna vaccine and one of the boosters.

According to the results, a 50 µg dose of the standard booster caused a 20-fold increase in antibody levels against Omicron. However, six months later, these levels decreased 6.3-fold. Moreover, antibodies against Omicron fell faster than those against previous strains.

Professor David Montefiori, the study’s co-author, called the drop in antibodies similar to one seen against delta variant. According to him, the low levels do not equal zero protection. The body’s memory B cells still have immunologic memory that quickly produce antibodies in case of exposure. 

This is not uncommon for mRNA vaccines or for vaccines in general.

Dr. David Montefiori, study author

However, the declining booster strength likely means a fourth booster dose might soon become authorized around the world. Moreover, there is a looming threat of future viral strains becoming more resistant to current vaccines.


Rolando Pajon et al, SARS-CoV-2 Omicron Variant Neutralization after mRNA-1273 Booster Vaccination, New England Journal of Medicine (2022). DOI: 10.1056/NEJMc2119912


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