Moderna is now starting trials on a new booster dose for its COVID-19 vaccine that has been designed to target the Omicron variant of the coronavirus. The company said Wednesday that a mid-stage study is now being conducted.

The announcement comes just a day after Moderna's rival Pfizer announced a similar trial for its own vaccine booster specifically designed to target the Omicron variant.

Moderna said that while its original third dose booster shot had proven effective in increasing the resistance of patients against the Omicron, it found that the levels of neutralizing antibodies declined after six months. Moderna clarified that neutralizing antibodies effective against Omicron were still detectable in patients even after six months.

For those who only had two shots, around 85% of participants had detectable neutralizing antibodies against the Omicron variant one month after the second dose, but only 55% had neutralized the variant after seven months.

While studies have shown that Omicron causes milder COVID-19 symptoms than earlier variants, Omicron has swiftly become prevalent in many regions of the world, pushing rising infection rates and putting pressure on healthcare systems. The variant is now responsible for 99.9% of COVID-19 cases in the United States, according to the U.S. Centers for Disease Control and Prevention. The agency said the remaining 0.1% is made up of the Delta variant.

Pfizer and BioNTech were first to announce that they are starting trials on a new third dose booster shot designed to combat Omicron. The companies made their announcement on Tuesday.

Moderna said it would begin trials to gauge the effects of its Omicron-specific booster shot in adult participants aged above 18. The test subjects will include those that had already received two doses of its original COVID-19 vaccine, mRNA-1273. Other subjects will be those that received the two doses plus the third booster dose of the same vaccine.

The company said its trials would involve around 600 participants in the U.S., 300 of those who had received two shots and 300 who received the two shots plus the original booster. Moderna has promised to share the trial's findings with public health officials so that they may make evidence-based judgments on the optimal coronavirus booster approach for the public in the coming months.

The CDC previously conducted studies, which found that the mRNA booster shots provided by Pfizer and Moderna were effective in the adverse effects of the Omicron variant.

A separate study conducted in Israel showed that a fourth dose of an mRNA vaccine boosted antibodies, but they found that it wasn't enough to prevent someone from getting infected with Omicron.

Several countries have already started rolling out third vaccine doses to their population as a way to curb the spread of the Omicron variant.