Prof Salim Abdool Karim Weekly COVID-19 UPDATES

10 April 2023
Many thanks to all those who sent me comments on polio after last week’s email. Pat Sidley write, “I remember the iron lung rather well and there is one in the foyer of Medical School of Wits.” Barry Schoub succinctly summarised our challenge with polio vaccination, “Will universal switching to inactivated vaccine and thereby sacrifice gut immunity still achieve high enough levels of immunity? Or should the push be for the much easier strategy in order to reach high levels of population immunity with oral vaccine?” And Lynn Morris reminded me about the importance of wastewater surveillance for cVDPV and how this helped Covid-19 wastewater surveillance, “The wastewater surveillance for COVID was built on the back of the polio program.”
Today’s missive is being written as I fly over the Atlantic, going to attend several meetings, including the Gates Global Health Scientific Advisory Committee, the NEJM Board meeting, the National Academy of Medicine Emerging Leaders Forum, CHAVD SAC, etc. Scientific meeting schedules are even more hectic now than pre-Covid as organisations get their meetings back on track. It’s almost as if Covid-19 is over – there are now so many in-person meetings, many without an online participation option. I, for one, find the in-person meetings much more stimulating and appreciate the personal interaction with friends and colleagues again, even though it is time-consuming, worsening climate change and costly (flights seem to be so much more expensive now).
But I cannot help but reflect on how we couldn’t do this just a few months ago without a vaccine requirement, masks and occasionally an on-site negative rapid test requirement.  There are 4 main reasons for this change:
  1. immunity is widespread, either from vaccination, natural infection or both. The latter, which provides hybrid immunity, is probably an important contributor due to its added protection.
  2. While new variants of concern were emerging every 6-9 months initially, leading to new waves, we have not had a new variant of concern in the last 15 months. And the risk of a new variant of concern recedes with each passing day. We know that new variants continue to emerge, but they are sub-variants within the omicron lineage that do not rise to the status of variant of concern, and they do not pose a significant threat since some level of omicron immunity is widespread, even though new omicron variants can escape some antibody immunity.
  3. This combination of immunity and the lack of variants with complete escape, makes us more confident that even if we inadvertently interact with someone with Covid-19, that the infected person will likely be minimally infectious with low viral load and that we would have sufficient protection against this.
  4. As a result, we have progressively come to terms with this virus and have developed tolerance to the risk involved, as this risk has receded, though there are still outbreaks (and superspreading events) from conferences and meetings. But our willingness to run this gauntlet, without giving it a second thought, is also driven by the fact that we are the survivors, whether we have survived natural infection or avoided getting infected at all and so are less concerned about an enemy we have dealt with and overcome previously. 

While we have adapted to this virus over the last 3+ years, the virus has continued to adapt to our protection against it. While there are over 600 omicron variants circulating worldwide, the latest variant in the evolution of the virus is XBB.1.16, which is now spreading in many countries    (Figure 1).  I have not yet seen data on the extent of cross-neutralisation from past immunity stemming from omicron BA.1, BA.5 or XBB.1.5 infection and so the extent to which our vaccine and natural immunity will protect us is not known. However, the mutations and their likely effects do not ring any alarm bells off at present.  


XBB.1.16 has spread to several countries, including the US (Figure 2).  While XBB.1.5 still dominates in the US, XBB.1.16 has been reported from several states. Maria van Kerkhove made the important point in her Science editorial this week that the continual evolution of the virus makes the timely sharing of viral sequence data very important. 

The extent to which XBB.1.16 or its sub-lineages will lead to widespread infection depends on their immune escape capabilities and their ability to be more transmissible. In Figure 3 below, which I have included in a past missive, the ability to become a dominant variant is substantially influenced by the transmissibility of the new virus. The variants of concern and the new omicron sub-lineages have continued to evolve to become more infectious, which each new variation of the virus having higher transmissibility. But this cannot continue ad infinitum – it has to come to a point where there are no or only small increases in transmissibility, too small to enable the new variant to become a new dominant variant, at which point the existing circulating strain will remain dominant as the endemic form of the virus, spreading periodically in relation to waning immunity rather than increased transmissibility.

As the world moves in this direction, protecting the elderly and vulnerable is going to become the mainstay of our approach to Covid-19. In this regard, the protection offered by a combination of vaccination and early treatment is going to be important to keeping infections, hospitalisations and deaths low. For this approach, testing is going to be key. Testing is key to identifying staff and others who may pose a risk to the elderly, especially in old age homes. In Figure 4 below, a study showed the benefit of testing staff and the elderly in old age homes. Testing is need for both early treatment initiation with drugs like Paxlovid and for initiation of public health measures such as quarantine to reduce the risk of exposing the elderly to infected individuals.

I am concluding this week’s email with a fun fact - a fascinating discovery in the world of mathematics, referred to as the “einstein” tile. The name has nothing to do with Albert Einstein, it is derived from the search for “one tile” (Figure 5). For decades, mathematicians have been trying to find a single tile that could be laid down infinitely without creating a repeated pattern. About 50 years ago, a combination of 2 tiles was described that could achieve this. But now, David Smith has found a hat shaped tile that can achieve this as a single tile. I was struck by the shape of the tile and its ability to be laid down without creating any pattern. It struck me how even a seemingly simple problem like this required such a long time to reach a solution – but now it has been solved!

Have a great week.


Salim S. Abdool Karim, FRS
Director: CAPRISA
CAPRISA Professor of Global Health: Columbia University