Covid-19 Weekly Updates

Prof Salim Abdool Karim Weekly COVID-19 UPDATES

Almost there!! Just a few more days before the cases drop below the threshold and the omicron wave is defined as ended. This week’s commentary is mostly on slide 1 and some interpretations as to whether omicron means that we are heading to endemnicity:

1. The 7-day moving average of new cases in South Africa is almost at 5 cases per 100,000 population per day, which is the cutoff I have used to define the start and end of a wave (very similar to the official government defined cutoff value). So, why the impatience for the end of the wave? Because we will then start the 3 month fallow period of low transmission – the inter-wave period has been quite consistently about 3 months (between waves) and if that trend continues post-omicron, then we should get a 3 month break when cases just don’t go up, even when restrictions are removed. This cyclical pattern is more easily discerned in smaller countries than bigger ones. In South Africa, SARS-CoV-2 is clearly cyclical.
2. Good news: reported Covid-19 deaths AND excess deaths are down this week – a clear sign that we are not going to see a delayed mortality. A further signal that the wave is coming to an end.
3. An interesting trend is the wave duration – from 1^st to 4^th wave, the waves were 74 days, 76 days, 126 days and about 52 days (depending on when it ends). So, omicron comes fast and goes fast. This trend is also evident in the UK and US – most clearly seen in New York.
4. Looking at slide 1, each successive peak (7-day moving average) is higher across the 4 waves. This reflects transmissibility as a key trait required to displace an existing variant.
5. The number of admissions: 70,498 in wave one, 90,333 in wave two, 128,658 in wave three and 42,765 in wave four. While the epidemic has shown an increase in admissions across the 3 waves despite increasing natural immunity after each wave (vaccination started too late to impact the first 3 waves), wave 4 has seen a substantial drop in admissions! This could reflect on increasing virulence from D614G to Beta to Delta. That overall trend across the 3 waves has now turned. Is it going to stay turned or is it going to back to the trend present up to Delta? Difficult to tell, though some are claiming that omicron is the path to endemnicity. This virus is too unpredictable to make such a statement. The main reason for its unpredictability is that each new variant does not emanate from past variants ie. Beta is not a mutation of alpha or delta is not a mutation of beta. Each of the 5 variants of concern evolved independently of each other and so there has been no way to predict how the next one is going to behave based on the past variants. One positive note though, a new variant will almost certainly have to have increased transmissibility to displace omicron, which is rapidly becoming globally dominant. It would be difficult (not impossible) to have increased transmissibility if a new variant makes people more sick to the point where they stay at home or in hospital and stop spreading the virus. For a new variant to have higher transmissibility and higher pathogenicity to cause more severe disease will need a mutation that extends the pre-symptomatic infectious period, ie. most of the transmission needs to occur before the person becomes clinically ill.
6. So, predictions of omicron being a low transmission endemic variant are premature – we need to see a clear trend with the next 1 or 2 variants in the opposite direction to the trend of the first 3 waves to make that prediction. In other words, we have no trend yet except the general trend of the first 3 waves which has not been followed by the omicron wave. Will the next variant follow the trend of the first 3 waves or follow the new trend set by omicron. It depends on whether you are an optimist or pessimist. It depends on how badly you want to believe that things will not get worse. Given that each variant is being created independently of past variants, it would take a brave person to guess which trend is going to be followed…

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