A recent study suggests that Covid-19 vaccines targeting only the omicron variant may offer better protection than bivalent vaccines that target both the omicron variant and the ancestral SARS-CoV-2 strain. The study's findings are based on analyzing people's responses to natural infections rather than a randomized trial, which is considered the gold standard in medical evidence.
Bivalent vaccines, which include proteins from both the initial coronavirus strain and the omicron variant, are currently being offered in several countries, including the UK, Australia, New Zealand, and Canada. However, in the US, vaccines are based solely on the omicron variant.
The initial vaccines used during the pandemic were developed based on the spike protein of the original coronavirus strain that emerged in early 2020. However, the emergence of the omicron variant in late 2021 quickly replaced previous strains. Despite being vaccinated against the original virus, many people still became infected with omicron, although the vaccines remained effective in reducing deaths and hospitalizations.
Antibodies against the SARS-CoV-2 virus can vary among individuals depending on their exposure to different spike proteins, either through infections or vaccinations. This phenomenon, known as immune imprinting, has raised concerns that antibodies optimized for the original virus may limit the immune response to omicron and future variants. Similar observations have been made with other viruses, such as influenza.
A recent study conducted in China found that natural exposures to omicron after receiving a dose of an ancestral vaccine led to an increase in omicron-specific antibodies among individuals. This suggests that omicron-only vaccines could be effective in mimicking these natural exposures.
The study's findings indicate that there may not be a need to include the original spike protein in vaccines, as it does not significantly enhance the immune response against omicron. Experts suggest that if the goal is to target omicron more effectively, an omicron-only vaccine may be necessary.
In summary, the study highlights the potential benefits of omicron-only vaccines in providing better protection against the dominant omicron variant. However, it is important to note that the findings are based on natural infections and further research, including randomized trials, is needed to confirm these results.