New Study: XBB.1.16 will likely spread worldwide displacing XBB.1.5. Evolution Continues Towards Immune Evasion and Suppression
Our evolutionary advantage is that we can build tools to significantly reduce transmission
The first study to come out on Arcturus (XBB.1.16) was published on April 9, 2023. The study says that “XBB.1.16 had an effective reproductive number (Re) that was 1.27- and 1.17-fold higher than the parental XBB.1 and XBB.1.5, respectively, suggesting that XBB.1.16 will spread worldwide in the near future.”
This research indicates that the immune evasion capacity of XBB.1.16 is comparable to XBB.1.5. They say that the increased fitness of XBB.1.16 may be attributed to one or both of the following factors: (1) alterations in its antigenic properties that differentiate it from XBB.1.5, and/or (2) mutations in non-structural viral proteins that enhance its replication efficiency. The authors of the study did not expand on this, and more research is necessary, but let’s dig into the two options they presented.
Antigenic properties refer to the specific characteristics of this variant that trigger the immune system to mount a response against it. In the case of viruses, antigens are usually proteins found on the surface of the virus particle. Any changes in these proteins, such as mutations or structural modifications, can alter the way the virus interacts with the immune system.
If XBB.1.16 has alterations in its antigenic properties that differentiate it from XBB.1.5, this means that the viral proteins present on the surface of XBB.1.16 are distinct from those of XBB.1.5. As a result, the human immune system may not recognize XBB.1.16 as effectively as XBB.1.5, allowing it to spread more efficiently in the human population. Additionally, if the altered proteins are less effectively targeted by existing vaccines or immune responses from prior infections, this could contribute to XBB.1.16's increased fitness advantage.
Since we know that antibodies are evaded by XBB.1.5 and that the level of that evasion hasn’t changed based on this study, it is possible that the reduced efficacy of the immune response against XBB.1.16 is due to evasion of T-cell responses rather than antibodies. Although this study did not investigate the specific immune mechanisms involved in the observed immune evasion, it is plausible that XBB.1.16 has developed mutations in non-structural viral proteins that enable it to evade T-cell recognition and clearance more effectively than XBB.1.5, leading to a higher level of viral replication and persistence. When we dug into the research on the mutations, we found that this became more plausible, not less.
The replication cycle of a virus involves multiple steps, and each step is facilitated by viral proteins. Mutations in these proteins can alter the way the virus interacts with host cells and can lead to changes in viral replication efficiency.
Non-structural viral proteins, in particular, play a critical role in the replication process by helping the virus evade the host immune response, hijacking cellular machinery, and assembling new virus particles. Mutations in these proteins could enhance the virus's ability to complete these steps more efficiently. If XBB.1.16 has mutations in its non-structural proteins that contribute to increased replication efficiency, this would allow the virus to build a greater viral load and a higher chance of transmission to other people. Additionally, the enhanced replication efficiency may enable the virus to better establish persistent infections in viral reservoirs, allowing it to persist and wait for the next variant to potentially recombine into a more evolved variant than either of the two parental variants that met inside the person hosting the persistent infection.
Additional studies are necessary to investigate the specific immune evasion mechanisms employed by XBB.1.16 and their impact, but we should take these changes seriously. This situation could lead to long-term health issues for hundreds of thousands, if not millions, of people. It may also result in unpaid sick days and cause children to lose valuable time from school, all of which can harm the economy both now and in the future. Fixing these problems after people have already been infected is more difficult than taking proactive steps now to reduce transmission, limit exposure, prevent persistent infections, and stop aiding in COVID's evolution.
COVID has had an evolutionary advantage over us from the beginning. It can rapidly evolve around our immune system responses and treatments. The more treatments we use during widespread transmission, the stronger the virus becomes. Our evolutionary advantage is that we can build tools to significantly reduce transmission, but we are not investing in the necessary systems to give us that advantage.
If we take proactive steps to increase filtration and ventilation to maintain CO2 levels at 600 ppm with HEPA level filtration, we can be more at ease. Since that hasn't happened yet, this variant will likely spread quickly through schools and homes. Closing schools for summer break a few weeks early should not be ruled out. Schools should use the extra time to invest in systems that can significantly reduce transmission. This would be a significant step towards preventing the endless waves of illness and death, protecting children, parents, communities, and economies for years to come. It is the single most important thing we can do as a society to invest in our future. We must work Together Against COVID Transmission.
