Explaining the differential severity of COVID-19 between Indians in India and the UK

严重急性呼吸综合征冠状病毒2 （SARS-CoV-2）是一种病毒感染；虽然许多人会出现轻微症状并迅速康复，但其他人会发展成严重的冠状病毒病（COVID-19），导致住院或死亡。许多研究表明，严重的COVID-19在老年人、超重或有现有健康状况的人群中更为常见。在英国和美国等国家，COVID-19对包括印度裔在内的少数民族人口产生了更大的影响。一种解释是，这些危险因素在印度人口中的流行率高于大多数人口。相比之下，印度是全球COVID-19死亡人数最少的国家。这导致人们认为，与居住在其他国家的印度人相比，居住在印度的人可能不太常见。对此有几种合理的解释；首先，居住在印度的人可能比居住在其他国家的印度人更多地接触阳光，这可能导致维生素d水平更高。其次，由于更多地接触其他感染，居住在印度的人可能对COVID-19有更强的免疫力。这与社会经济地位有关，因为生活在卫生条件差的过度拥挤家庭中的人可能比海外的印度人口更容易感染疾病。第三，与生活在高收入国家的印度人相比，生活在印度的人可能更少肥胖，也更少患有预先存在的疾病。印度居民的身体质量指数较低可能是由于卡路里摄入量较低或身体活动较多，这两者都可能降低患严重COVID-19的风险。虽然真正的生物学差异可能解释了印度居民感染严重COVID-19的风险较低，但可能还有其他解释，例如COVID-19数据质量和人口年龄结构的差异。例如，由于对这种病毒的污名，生活在印度的人可能不太可能因为感染COVID-19而去医院，或者他们更有可能死在家里，而不是在医疗机构。这意味着，与其他国家相比，印度可能没有很好地掌握死亡原因，严重COVID-19患者的真实人数可能被低估。迄今为止，没有一项研究完全回答了COVID-19在印度和其他国家的印度人口之间的严重程度是否真的不同。在这项研究中，我们将比较英国和印度印度人患严重COVID-19的风险，并确定可能的解释。我们将进行两项大型研究。第一项研究将使用英国5040万印度人的匿名医疗记录，并采访生活在印度城市和农村的22万人的数据。我们将首先比较曾经患过严重COVID-19的人口比例，严重COVID-19的定义是因COVID-19住院或死亡。然后，我们将探讨严重COVID-19流行率的差异是否可以用数据质量的差异、两个人群的年龄结构或关键危险因素流行率的差异来解释。我们的研究将解决关键问题，即COVID-19在印度是否被低估，首先，通过采访曾经因COVID-19症状入院的个人，其次，通过使用一种称为口头尸检的方法采访有关其家庭成员死亡的人。第二项研究将使用作为印度两项研究的一部分收集的详细生物学和信息，深入研究COVID-19与既往感染或疫苗接种、肥胖、合并症和维生素d之间的联系。我们预计，我们的研究将产生影响，包括制定考虑到全球印度人口具体需求的COVID-19预防和管理战略。更深入地了解导致印度裔人患上严重COVID-19的因素。

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a viral infection; while many people experience mild symptoms and recover quickly, others go on to develop severe coronavirus disease (COVID-19) resulting in hospitalisation or death. Many studies have shown that severe COVID-19 is more common in people who are older, overweight, or with existing health conditions. In countries such as the UK and USA, COVID-19 has had a greater impact on ethnic minority populations, including those of Indian ethnicity. One explanation is that the prevalence of these risk factors is higher in Indian populations than in the majority population. In contrast, India has the lowest number of COVID-19 deaths worldwide. This has led to the belief that severe COVID-19 may be less common in people residing in India than in Indian people in other countries. There are several plausible explanations for this; Firstly, people residing in India may have greater environmental exposure to sunlight than Indians residing in other countries, which may result in higher levels of vitamin D.Secondly, people living in India may have greater immunity to COVID-19 resulting from greater exposure to other infections. This is related to socioeconomic status as people living in overcrowded households with poor sanitation may be more likely to contract infections than Indian populations overseas. Thirdly, people residing in India may also be less obese and have fewer pre-existing conditions than Indian people living in higher-income countries. Lower BMI in Indian residents may result from lower calorie intake or higher physical activity - both of which may lower the risk of severe COVID-19. While it is possible that real biological differences may explain the lower risk of severe COVID-19 in Indian residents, there may be alternative explanations such as differences in the quality of COVID-19 data and age structure of the populations. For example, people living in India may be less likely to visit the hospital with COVID-19 due to stigma around the virus, or they may be more likely to die at home instead of in a medical facility. This means that the cause of death may be less well captured in India than in other countries, and the true number of people with severe COVID-19 may be underestimated. To date, no study has fully answered whether the severity of COVID-19 truly differs between Indian populations in India and in other countries. In this study, we will compare the risk of severe COVID-19 between Indians the UK and India and identify possible explanations. We will conduct two large studies. The first study will use the anonymised medical records of 50400,000 Indians in the UK and interview data from 220,000 people living in urban and rural India. We will first compare the proportion of the population who have ever had severe COVID-19, defined as either going to the hospital for or dying from COVID-19. We will then explore whether differences in the prevalence of severe COVID-19 can be explained by differences in data quality, the age structure of the two populations, or differences in the prevalence of key risk factors. Our study will address the key issue of whether COVID-19 is underestimated in India by firstly interviewing individuals ever admitted to hospital about COVID-19 symptom, and secondly, by interviewing people about deaths of their family members using a method known as a verbal autopsy. The second study will use detailed biological and information collected as part of two studies in India to conduct an in-depth examination of linked between COVID-19 and prior infections or vaccinations, obesity, co-morbidities, and vitamin D. We expect that the impacts of our research will include the development of COVID-19 prevention and management strategies which take into account the specific needs of Indian populations worldwide, and a deeper understanding of factors which lead to the development of severe COVID-19 in people of Indian origin.