The study looked at DNA from 2,240 people with severe Covid-19. This is a small sample compared with the 20,000 participants planned for DecodeME. However, a smaller sample is enough when you are looking for a strong genetic affect, as we were pretty sure would be the case here.
And our study did indeed find several genetic variants that were significantly more common in people with severe Covid than in controls from the general population.
Several things make us confident that our results are reliable. Firstly, the study identified a strong genetic link that had just been reported in another, slightly smaller, study of Italian and Spanish severe Covid-19 patients. Secondly, we were able to replicate four of our novel findings using data from the direct–to-consumer genetic testing company 23andMe and from the international COVID-19 Host Genetics Initiative.
The four newly identified genetic risk variants each increased the risk of severe illness by around 20%. So someone who has all three variants would have roughly twice the risk of getting severe Covid (if they became infected) compared with someone with none of them.