Why is the Covid-19 mortality rate so high in the Western Cape?
Altitude plays a role, as do UV radiation levels and the weather
Since the start of the Covid-19 pandemic at the end of 2019 there has been much speculation about whether the impact of the coronavirus varies at different altitudes. Currently, the mortality per million people in the Western Cape is 279.5. This is 19 times higher than the mortality per million people in Gauteng.
Why is this? One theory is that the proportions of people with HIV/Aids or TB could be higher in the Western Cape than in the rest of the country. It could also be that the age distribution in the Western Cape differs from that in other provinces.
However, according to the 2018 General Household Survey (GHS) this does not seem to be the case.
However, more than 60% of the population in the Western Cape live in the City of Cape Town, meaning a large number of people in this province live at sea level. Does this low altitude contribute to the high mortality rate in the province?
An epidemiological analysis of the Covid-19 pandemic by Arias-Reyes et al (2020) showed a decrease of prevalence and impact of the virus in populations living at altitudes higher than 2,500m. Their study analysed the occurrence of Covid-19 in China, Bolivia and Ecuador, and concluded that the Covid-19 mortality rate per capita decreases as altitude increases.
The US is currently one of the countries hardest hit by the Covid-19 pandemic. Most major cities in the US are at sea level, or near navigable rivers. If the weighted average altitudes of the five largest cities in each of the 52 states (or six, if the state capital is not one of the largest five cities) are compared to the number of deaths per hundred thousand people in each of the states, the scatter plot indicates that at altitudes higher than 300m the mortality rate is significantly lower.
Thus, states in the US with large, high-altitude cities are less affected by Covid-19.
The question is how to explain the apparent relation between mortality rate and altitude. There is an increase in solar ultraviolet (UV) radiation with altitude (Blumthaler et al, 1996). Some other factors related to altitude are solar elevation (the closer to the equator, the higher UV radiation levels); cloud cover (UV radiation levels are highest under cloudless skies); and pollution levels and ozone levels (ozone absorbs some of the UV radiation that would otherwise reach the Earth’s surface).
In an academic research paper submitted for publication by Bäcker (2020), he shows that there is slower Covid-19 morbidity and mortality growth at higher solar irradiance and elevation. His results suggest that transmission models should incorporate solar elevation, and that the impact of UV radiation on individual morbidity and mortality should be tested.
The lower UV radiation at sea level, as well as the large amount of cloud cover during the winter months, may further contribute to the high mortality rate in the Western Cape. Sunny winter days — typical in Gauteng and other inland provinces at this time of the year — may assist in restricting the spread of the virus in these provinces.
If altitude and UV radiation do play a role, the mortality rates of the inland provinces may continue to be lower than those of the coastal provinces
In SA, inhabited altitudes fluctuate considerably. According to the 2018 GHS, 58% of the SA population live in inland provinces, compared to 42% in coastal ones. If we accept the altitude and UV radiation hypothesis, we would expect the mortality rate in all three coastal provinces to be similar. The Western Cape, however, has more cloud cover and a lower solar elevation than the Eastern Cape and KwaZulu-Natal.
In the Western Cape, a larger percentage of people also live at sea level compared to the Eastern Cape (29% of the population live in Nelson Mandela Bay and Buffalo City districts) and in KwaZulu-Natal (34% of the population live in the eThekwini Metropolitan district).
Altitude and UV radiation are, of course, not the only factors influencing mortality, but within the SA context it could explain why the Western Cape has a higher mortality rate than the rest of the country. The general belief in SA is that the mortality rate in the Western Cape is higher because the province is “ahead” of other provinces on the inevitable upward surge of infections. This implies that other provinces will catch up in terms of mortality rates in the coming months.
However, if altitude and UV radiation do play a role, the mortality rates of the inland provinces may continue to be lower than those of the coastal provinces.
Bäcker (2020) suggests that the significant reduction in the pandemic’s growth observed at higher solar elevations across geographic locations can help governments plan their response to the crisis. He also suggests that, should sunlight give more resistance to Covid-19, the correct policy may be one that achieves social-distancing without locking people in.
What are the implications if this hypothesis holds water? We recommend the following.
First, a much earlier lifting of the lockdown for the inland provinces. Second, though difficult to achieve, vulnerable and older people could be moved to higher altitude areas with more winter sun and, thus, UV radiation. Third, medical resources and personnel allocation could be prioritised in the higher risk provinces, that is areas in the Western and Eastern Cape.
Fourth, new methods to reduce the spread of the virus can be investigated if it can be established whether UV radiation, indeed, reduces its contagiousness. Lastly, since germicidal UV is a standard practice deployed in sterilisation protocols, UV lights can be used to sanitise surfaces and goods.
In conclusion, if the pandemic can be proven to have less impact in the inland provinces it will boost offshore investment in SA. It will also be beneficial for tourism in the coming spring and summer of 2020/2021. Striving to have less polluted air with higher levels of UV radiation in SA is a worthy cause, thus promoting renewable energy initiatives as they cause less air pollution than coal-fired power stations.
Mortality numbers in many other Southern African countries, such as Namibia, Angola, Botswana, Zambia and Zimbabwe, are very low (admittedly, these numbers are not necessarily reliable). All these countries receive summer rainfall, similar to the northern parts of SA, have a higher solar elevation and a high percentage of the population living at high altitude.
Recommendations made for SA’s inland provinces could also be implemented in these countries.
There are still many unknown factors regarding the virus. If the theory posited above is true, more research is needed to understand the exact reasons why higher UV radiation and altitude influence the spread and the mortality rate caused by the virus.
• Uys is an associate professor at Stellenbosch University, and Van der Merwe a business analyst.
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