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This past week has seen an acceleration in the month-long trend of rising levels of new but relatively mild COVID infections. The most reliable indicator of pandemic trends, viral counts in municipal wastewater, has been rising moderately but quite steadily since mid-July. As illustrated in our weekly composite chart, PCR test positivity rates among the minority of Ontarians still eligible for definitive testing have jumped quite sharply over the most recent two-week period. COVID hospitalizations, on the other hand, tend to provide a slightly lagging indicator of the severity of infections caused by the current mix of variants. That indicator has thus far remained low.
Turning to that viral mix, Public Health Canada has revamped its reporting on COVID variants, which now better captures the breathtaking proliferation of the XBB family of Omicron variants which account for essentially all new cases. The currently-dominant XBB strain, EG.5, is actually two sub-strains (EG.5.1 and EG.5.1.1) which together accounted for 53% of all new Canadian cases during the week of August 13th through 19th.
A recent CBC report puts that proliferation into perspective. The August 22 article was about an unusually-highly-mutated COVID variant, BA.2.86, which has recently been detected in multiple countries. It has more than 30 spike protein mutations compared to its BA.2 predecessor. While that sound scary, the article correctly points out that different does not imply more transmissible. Mutations are fundamentally random. The vast majority render the genome in question less “fit” rather than more. This one didn’t appear in the top 30 US variants published in the most recent US CDC report. The most fit (i.e., most transmissible) in that list was FI.1.5.1 which had multiplied its “market share” more than ten times in the previous week. If, as is likely, BA.2.86 is incapable of doing the same, then it will quickly disappear. If on the other hand, it proves to be equally or more transmissible in coming weeks, then we would definitely need to track the average severity of symptoms among those infected to see if some of those mutations present a danger to human health. All of the current XBB strains can evade prior immunity, whether from vaccination, previous infection or both but, except for those of us who are 70+ or immunocompromised, that prior immunity more often than not keeps the symptoms relatively mild.
The current booster shot is formulated for BA.4 and BA.5 but provides reasonable protection against the XBB strains. The newer ones which should be available next month are formulated against XBB and will hopefully do an even better job. If BA.2.86 should to be dangerous, then the next generation of vaccines will undoubtedly include it in the formulation, though that would be many months away. Anyone whose most recent COVID vaccination was more than six months ago would be wise to get boosted prior to the coming reopening of our schools, which will inevitably accelerate the current rise in new infections.