Why You Need Omicron XBB Booster to Protect Yourself from Fast-rising Omicron EG.5.1 (Eris)?
A comprehensive look at the soon-to-be rolled-out COVID-19 vaccine against Omicron XBB effectiveness in protecting against the Omicron EG.5.1.
What is Omicron EG.5.1?
Omicron EG.5.1 is a sub-lineage of the Omicron variant of SARS-CoV-2, the virus that causes COVID-19. It is also known as V-23JUL-01 or XBB.1.9.2.1, according to the World Health Organization (WHO) and the UK Health Security Agency (UKHSA), respectively.
Omicron EG.5.1 has one additional spike mutation compared to its parent lineage, XBB.1.9.2, which is also a descendant of Omicron. The spike protein is the part of the virus that attaches to human cells and allows infection. Mutations in the spike protein can affect how easily the virus can spread and how well it can evade the immune system.
Omicron EG.5.1 was first detected in Asia in May 2023, and has since been reported in several countries around the world, including the UK, where it is now spreading rapidly. It accounts for about 15% of all COVID-19 cases in the UK as of August 4, 2023, making it the second most prevalent variant after Arcturus XBB.1.16.
The UKHSA and the WHO are closely monitoring Omicron EG.5.1 to assess its impact on public health and vaccine effectiveness. So far, there is no evidence that Omicron EG.5.1 causes more severe disease or increases the risk of hospitalization or death compared to other variants.
From November 2021, SARS-CoV-2 omicron has been the most dominant lineage of SARS-CoV-2 and it has been evolving ever since to form sub-lineages or descendants.
Last year, the vaccine administered against SARS-CoV-2 targeted the omicron sub-lineage BA5, because at the time it was the most dominant omicron sub-lineage.
Starting January 2023, omicron sub-lineage XBB has been replacing BA5 to become the most dominant omicron sub-lineage, but not until August 2023 when omicron EG.5.1 took over.
The annual booster vaccine that will be given from October 2023 onwards is specifically designed to target XBB.1.5, a sub-lineage of the Omicron variant of SARS-CoV-2. However, as the data in the image above shows, XBB.1.5 is losing its dominance and being replaced by EG.5.1
Many people are wondering if they should get the booster shot against XBB, since the most prevalent sub-lineage of the Omicron variant of SARS-CoV-2 is now EG.5.1 in many regions.
From an Evolutionary perspective…
As an evolutionary virologist, I enjoy explaining reality with my evolutionary background. In this article, I will discuss how the XBB booster can protect you from EG.5.1, using two evolutionary perspectives:
1. In relation to other XBB sub-lineages
Omicron is a descendant of omicron XBB.1.9.2 with an additional mutation in the Spike protein, F456L. The notation means that in the Spike protein amino acid position 456 of EG.5.1, the amino acid Leucine replaces Phenylalanine compared to XBB1.9.2
Mutation F456L is a convergently growing mutation, which means that it has emerged independently in different lineages of the virus. It may have a slight growth advantage over other variants, meaning that it can spread faster and become more dominant.
Based on the provided information, it can be concluded that EG.5.1 is closely related to the XBB sub-lineage. In fact, some virologists refer to EG.5.1 as XBB.1.9.2.5.1. Therefore, a vaccine developed to target other XBB variants should also be effective against EG.5.1.
2. In relation to the XBB.1.5 booster vaccine.
As mentioned earlier in this article, the October 2023 Booster shot is mainly intended to safeguard against XBB.1.5. This is not unexpected, given that the image provided above indicates that XBB.1.5 has been the dominant strain recently.
Comparing XBB.1.5 and EG.5.1, the only additional mutations in the Spike protein are F456L and Q52H. F456L has already been discussed. Q52H means that the amino acid at position 52 of the spike protein, which is used by the virus to enter human cells, is changed from glutamine (Q) to histidine (H).
Q52H has been detected in some sublineages of XBB.1.9.1, which is one of the variants of interest (VOI) identified by the WHO. These sublineages include XBB.1.9.1.5, XBB.1.9.1.7, and XBB.1.9.1.18.
If the booster is effective against the parental lineage XBB.1.9, it is highly probable that it will also be effective against EG.5.1.
Conclusion
If the XBB.1.5 booster can protect against the majority of XBB sub-lineages, it is likely to also provide protection against EG.5.1. This is because even though EG.5.1 is an EG lineage, it is still closely related to XBB.
