On Thursday, Moderna announced that it had requested the US Food and Drug Administration (FDA) for emergency authorization for a second booster shot of its COVID-19 vaccine for all adults above 18 years of age, who had been given an initial booster shot of any of the approved COVID vaccines.

The request was based partly on recent data from the United States and Israel about how effective was the Moderna shot against the Omicron variant. 

Previously, Pfizer-BioNTech had also requested emergency approval for a second booster shot, for adults aged 65 and older, which was also based on two Israeli studies which showed enhanced immunogenicity and lower rates of infections and severe illness with an additional booster.

The first study showed that people aged 60 and older who received an additional booster dose had 2 times lower rates of confirmed infections and 4 times lower rates of severe disease.

The second study, which included Israeli healthcare workers aged 18 and above, showed significantly high levels of antibodies among those who received the second booster dose compared to those who did not.

Recent studies showed that while the third dose of an mRNA vaccine increased the antibody levels higher than the initial doses, the second booster dose (or the fourth dose) would return the individuals levels to that same highly-elevated level. (ETHealthWorld - AFP, March 18, 2022)