According to a Japanese study published in the journal Open Forum Infectious Diseases, bivalent vaccines that target the newer COVID variants, particularly Omicron and sub-variants, are very effective. Bivalent vaccines that target the newer COVID variants, particularly Omicron and sub-variants, performed well, according to two studies.

However, primary vaccines showed rapidly waning protection from SARS-CoV-2 infections in the post-Omicron era. In this study, the researchers measured the effectiveness of bivalent (two-strain) COVID-19 mRNA vaccines against symptomatic infection during the BA.5-dominant period in Japan.

This was one of the first trials to assess the efficacy of the newer BA.4/BA.5-containing bivalent vaccine developed in 2022 to target highly transmissible Omicron subvariants. The bivalent vaccination was shown to be 72% effective against Omicron infection in a trial consisting of 6,191 participants. The study also showed that the bivalent vaccine was 35% more effective in comparison to monovalent vaccines after 3 to 6 months of immunization.

However, the researchers noted that the bivalent vaccines were not as effective against the Omicron subvariants (85%) as the monovalent vaccines were against the ancestral strain (Alpha) and Delta variants (95%).

The second study, published in JAMA Network Open, used a meta-analysis of 40 studies to determine the efficacy of a primary vaccination cycle involving the monovalent (one-strain) vaccine against both laboratory-confirmed Omicron infection and symptomatic disease. At 6 months after the last dose, estimates of the efficacy of a primary vaccination cycle against laboratory-confirmed Omicron infection and symptomatic disease were both less than 20%.

The findings of the study also showed that, in comparison to symptomatic disease caused by the Delta variant, the effectiveness of the monovalent vaccine was 79.6% after 1 month of completion of the primary vaccination cycle. Booster doses of vaccination increased the effectiveness of the vaccine against Omicron. However, after 9 months following booster injection, the effectiveness of the jab was found to have been lowered by 30 to 20% against laboratory-confirmed infection and clinical sickness. 

(Source: https://www.newkerala.com/news/2023/55359.htm )