Prof Salim Abdool Karim Weekly COVID-19 UPDATES
Figure 3 below provides a week-by-week distribution of variants in South Africa, courtesy of the Network for Genomic Surveillance in South Africa. The omicron sub-variant XBB.1.5 has increased substantially in the last week replacing BA.5 and BQ.1.
This kind of change in variants would be expected to accompany an increase in cases as the XBB.1.5 sub-variant transmits faster than the sub-variants it is replacing. However, reported cases show only minor increases (Figure 2). I suspect that South Africa is experiencing a rapid rise in cases due to XBB.1.5, but that this increase is much smaller than we would normally see with a new variant. Further, the increased cases are likely to be mostly mild and asymptomatic due to pre-existing immunity, which is predominantly hybrid immunity in people >60 years. This highlights the problem that test-positive case reporting may no longer reflect case rates in the community as the proportion of cases that are asymptomatic increase.
I wondered whether the changes I would expect to see in light of the change in variant distribution in South Africa may be reflected in the waste-water surveillance instead. According to the SA MRC website dashboard for waste-water Covid-19 surveillance, the number of positive samples shows a small increase and the viral load in the samples shows no obvious recent increase. So, I may be wrong in expecting an increase in cases with the new sub-variant. Nevertheless, I am keeping a watching brief on the reported cases and will note changes in the weekly missives.
This week, I want to explore the range of other epidemics across the world. In figure 4 below, I have listed the 5 most reported epidemics for each of the last 4 years.
This week, we have a new epidemic!
Equatorial Guinea reported that it was experiencing an epidemic of Marburg virus infection, with 25 cases and 9 deaths. Cameroon has reported 2 suspected cases in the region near the Equatorial Guinea. Marburg is only spread by close personal contact with infected body fluids. Nosocomial transmission is important. It is not spread by the respiratory route.
In the 55 years since this virus was discovered in laboratory workers in the German city of Marburg (and Frankfurt), there have been about a dozen Marburg virus epidemics (Figure 6). The largest outbreak of Marburg occurred in Angola about 20 years ago. The case fatality rate was about 90% in that Angola outbreak.
Infection in humans is a Zoonosis, from bats to humans. Note that the Marburg virus is similar to the Ebola virus.
This Marburg outbreak in the distant land of Equatorial Guinea is not one that we can ignore. While it is unlikely to spread much beyond the country’s borders, it is a reminder that we need to be prepared for epidemics and pandemics.
In 1986, when I was doing my specialist Microbiology-Virology registrar training at the Nelson Mandela Medical school, I was responsible for the KwaZulu-Natal haemorrhagic fever ward located at King Edward VIII Hospital. The ward was created because of a local scare that Congo-Crimean Haemorrhagic Fever virus was in circulation following the Marburg outbreak in South Africa a few years earlier. The ward was a pre-fab building and I designed it with negative air pressure, barrier nursing and minimal need to directly touch patients. We did drills to practice our admission and care procedures every 3 months. Fortunately, throughout my time in charge of this ward, we had no haemorrhagic fever cases.
Have a great week.