New insights into the role of obesity in coronavirus disease and transmission.
Please note: This is a scientific analysis; it does not advocate “fat shaming”.
Covid severity is known to be strongly correlated with age, or, more precisely, with frailty. In most countries, the average age of covid deaths is slightly above average life expectancy, and in many Western countries, about 50% of covid deaths occurred in nursing homes, which comprise about 1% of the population and whose residents have a remaining life expectancy of about one year.
This is why it is essential to distinguish between covid fatality rates (IFR) in nursing homes (about 30%) and in the general population (about 0.2% to 0.6%, 1% at 80, and <0.05% in people below 40). While it is important to protect nursing homes, it is also important to do so in a humane way.
In the non-elderly population, however, it has been shown that obesity is one of the most important risk factors for severe and fatal covid. SPR has previously shown that national obesity rates and national mortality rates appear to be strongly correlated (if calculated correctly). It has been thought that this might perhaps be due generally poor cardiovascular health in obese people.
Yet a new study published in the International Journal of Obesity has found that in obese covid patients, the majority of antibodies are non-neutralizing (i.e. they don’t inhibit infection) and even auto-immune (i.e. they attack the patient’s own tissue), leading to significantly higher levels of inflammatory markers in obese patients compared to lean patients (see charts below).
This result is consistent with another recent study by Stanford researchers, which found that “SARS-CoV-2 infects human adipose tissue and elicits an inflammatory response consistent with severe COVID-19.” Thus, it looks like it is the excess adipose tissue itself that exacerbates covid infection.
Given these results, one might expect that obese covid patients show higher peak viral loads, and do so for a longer period of time, than non-obese patients. And indeed, this is precisely what another recent study, published in the Journal of Infectious Diseases, has found. Of note, while obese patients generally have higher overall antibody levels, this is not a helpful property, as these antibodies generally have much lower neutralizing capability (see above).
In addition to higher viral loads, obese patients are also known to exhale more bioaerosols. Taken together, it appears possible that obese people might not only be at higher risk of severe covid, but that they might also play an important role in virus transmission. Similar results had previously been found in the case of influenza virus disease and transmission.
SPR has previously shown that East Asian countries with stunningly low coronavirus infection and mortality rates happen to be the very countries with the lowest obesity rates in the world, despite some of them having among the oldest populations in the world (e.g. South Korea and Japan). In contrast, places with high obesity rates – such as Latin America, the US, the UK, Eastern Europe and much of the Arab world – have seen the highest covid mortality rates in the world.
Competing explanations for the “East Asian covid miracle” have been early border controls, pre-existing immunity, or even genetic differences. While it is true that early border controls have been important in several countries (most of them islands, e.g. Taiwan, Singapore, Australia and New Zealand), they cannot explain the sustained success of some East Asian countries.
As for pre-existing immunity, one would expect to find it primarily in rural areas in northern Indochina (e.g. Laos, Vietnam and Myanmar), where the closest known relatives of SARS-CoV-2 are located, but not so much in urban areas in Japan and South Korea. Indeed, a recent study on Laos found cross-reactive (but not necessarily neutralizing) antibodies in about 5% of the general population and in about 20% of people with contact to bats and wildlife.
Genetic differences are still a theoretical possibility (e.g. concerning ACE2 cell receptor expression), but so far, no relevant differences have been identified.
In sum, the ‘obesity hypothesis’ continues to be a promising explanation for both coronavirus disease severity (in non-elderly people) as well as transmission dynamics. The obesity hypothesis might also explain why most Black African countries, but not South Africa and the North African Arab countries (with high obesity rates), have experienced rather low covid mortality.
However, it looks like the Delta variant, which was first detected in the spring of 2021 in India and which achieves significantly higher viral loads, got better at spreading among lean people and, perhaps for this reason, ultimately overwhelmed several South East Asian countries. This is true even for places like Japan and South Korea, but these high-income countries managed to vaccinate their elderly at-risk population prior to the Delta wave, thus protecting them, at least for now.
It had been feared that covid vaccines might be less effective in obese people (which is the case for some other vaccines), but so far this has not been found to be the case. Nevertheless, given the results above, people at high risk of severe covid, and especially obese people, may want to make sure they have access to the best early treatment options currently available.
See also: Obesity and the Pandemic: New Insights (June 2021)