Three doses of the Moderna mRNA COVID-19 vaccine are more than 99 percent effective against hospitalization for individuals infected with either omicron or delta coronavirus variants, according to a study published Feb. 21 by Nature Medicine.
Researchers led by a team from Kaiser Permanente Southern California conducted a study of 26,683 COVID-19 cases in the area caused by the delta or omicron variants in December 2021. Delta accounted for 16 percent of the infections, while omicron cases made up the remaining 84 percent.
Moderna three-dose vaccine effectiveness against hospitalization with delta or omicron infection was greater than 99 percent across the study population. Only four patients who had received three doses were hospitalized. They all had omicron infections, were older than 60 and had chronic diseases; one had a compromised immune system.
Six other study findings:
1. Researchers found high, durable three-dose effectiveness against delta infection but lower effectiveness against omicron infection, particularly among immunocompromised people.
2. Just one Moderna dose was 56.7 percent effective against delta infection and 20.4 percent effective against omicron.
3. Three doses were 93.7 percent effective against delta at 14 to 60 days, and 86 percent effective after 60 days. Against omicron, three-dose effectiveness was 71.6 percent at 14 to 60 days, and 47.4 percent after 60 days.
4. The full three-dose vaccine regimen was 70.9 percent effective against omicron infection in participants older than 65, while it was 64.3 percent among younger peers.
5. Three doses were 29.4 percent effective against omicron infection among 30 people with compromised immune systems, compared with 75.5 percent among non-immunocompromised peers.
6. Researchers said waning vaccine effectiveness against omicron within three months after the second dose indicates that a shorter interval between second and third doses may boost immunity.