In the ongoing battle against Covid-19, the U.S. Food and Drug Administration has granted emergency use authorization for new Covid-19 vaccines. The Centers for Disease Control and Prevention has also recommended these vaccines as boosters for all individuals above the age of 6 months. These new vaccines have been specifically modified to better match the currently circulating strains of the virus and are expected to reduce the severity of illness, hospitalization, and death among those infected with SARS-CoV-2, the virus responsible for Covid-19.
The newly approved vaccines, developed by Moderna and Pfizer-BioNTech, utilize the same mRNA technology as their earlier versions. However, the mRNA in these new vaccines has been altered to target the spike protein of the XBB.1.5 subvariant of the omicron variant. Early data suggests that this booster will stimulate the production of antibodies that can recognize this specific form of the virus, potentially providing improved protection against other circulating subvariants as well.
As we have witnessed throughout the pandemic, the virus continuously evolves over time. The initial vaccines, authorized in December 2020, contained mRNA that coded for the spike protein of the original SARS-CoV-2 virus. However, as viral variants with spike protein gene mutations emerged, the effectiveness of the original vaccines diminished, leading to the development of new formulations targeting newer viral strains.
For instance, in response to the surge in cases associated with the omicron variant, Moderna and Pfizer-BioNTech modified their vaccines from monovalent to bivalent. These boosters, authorized in August 2022, contained mRNA coding for the spike protein of the original virus as well as the BA.4 and BA.5 subvariants of omicron, which were predominant at that time. However, by the end of 2022, the prevalence of these subvariants had declined, and the XBB.1.5 subvariant of omicron emerged, necessitating the development of the latest vaccine formulations.
While XBB.1.5 was once the dominant variant, its prevalence has significantly decreased compared to the rise of another omicron subvariant called EG.5, which now accounts for approximately 25% of infections. Additionally, researchers are monitoring another subvariant known as BA.2.86 or Pirola, which possesses numerous mutations in the spike protein gene. Although the prevalence of BA.2.86 remains low, concerns persist about its potential ability to evade existing vaccines and be more transmissible than previous variants.
However, recent data suggests that the XBB.1.5 vaccine still provides protection against EG.5 and BA.2.86. Moderna's clinical trial demonstrated that their XBB.1.5-based vaccine generated neutralizing antibodies against these variants. Furthermore, a manuscript under review by researchers from Harvard University and Los Alamos National Laboratories suggests that BA.2.86 may not be as capable of evading immunity as initially feared.
While the new XBB.1.5 vaccine offers better protection against current Covid-19 strains, the virus will continue to evolve, requiring periodic updates to vaccines. Efforts are underway to develop a pan-coronavirus vaccine that can effectively target multiple coronaviruses, but until then, we may find ourselves engaged in a constant game of catch-up with the virus.