More from Denmark on BA.2
Immune Evasion Ups the Game
A very recent medRxiv preprint from the Statens Serum Institut of Denmark has some further data of interest on BA.2. doi: https://doi.org/10.1101/2022.01.28.22270044 Looking at household secondary cases occurring in a short time frame after the initial PCR diagnosis, they compared the transmissibility of Omicron (BA.1) and BA.2. They find that BA.2 is 34% more likely to be transmitted within the household. Not a surprising result given the rapidity with which it has overtaken BA.1 as the dominant virus in Denmark. Further stratification by vaccination status shows that the increase in transmissibility was only found when the index case was unvaccinated, suggesting perhaps that viral loads with BA.2 infection are lower in vaccinated breakthrough cases. Unfortunately the advantage in infectious potential of BA.2 over Omicron (BA.1) is greater in the vaccinated than in the unvaccinated, and even greater in the 3 dose boosted. That strongly implies an increase in antibody evasion compared to BA.1. That statement should not be misinterpreted as meaning that the vaccinated and boosted have a higher chance of getting infected than the unvaccinated, that certainly is not the case. But it indicates that BA.2 is a bit craftier in getting around our vaccine induced antibody defenses than Omicron. I think we should also consider the possibility that this variant might be able to cause reinfection in Omicron recovered people. That is of course speculative, and somewhat unpleasant to contemplate given the vast numbers of people recently infected with Omicron, who we hope have some duration of durable immunity.
BA.2 has yet to make an impact on the United States despite having been recorded in a majority of states in very low numbers. That’s not the case in India however, which has reported BA.2 replacing Omicron in three large states during December and January. The good news there, as in Denmark, is no apparent increase in disease severity compared to Omicron. Given the increase in transmissibility and the suggestion here of a higher degree of immune evasion, we should expect BA.2 to begin expanding in the US quickly. Here in Telluride, Colorado we expect to have a new probe available to detect BA.2 in the waste water stream very soon.