key: cord-275068-yr076sl6
authors: Ayoub, Fares; Sato, Toshiro; Sakuraba, Atsushi
title: Football and COVID-19 risk: correlation is not causation
date: 2020-09-03
journal: Clin Microbiol Infect
DOI: 10.1016/j.cmi.2020.08.034
sha: 
doc_id: 275068
cord_uid: yr076sl6

nan

To the Editor, 1

As the world battles the Coronavirus Disease 2019 (COVID-19) pandemic, wading through the deluge of 2 published COVID-19 research has become a challenge for clinicians. Despite a strong push for the 3 practice of evidence-based medicine over the past decades, a search of COVID-19 literature in recent 4 months paints a different picture. The use of hydroxychloroquine has been the 'poster child' for the 5 importance of conducting randomized controlled trials (RCTs), initially showing promise in uncontrolled 6 studies [1] and even being recommended by governmental leaders, only to later show no benefit in 7

RCTs. [2] Similarly, many observational studies have reported on risk factors for COVID-19. A recent 8 genome wide association analysis (GWAS) has implicated that blood group A patients had a higher risk 9 of severe COVID-19 compared to other blood types,[3] while other studies have found associations 10 between vitamin D levels/latitude, and Bacille de Calmette et Guérin (BCG) vaccine and mortality to 11 COVID-19. [4] Based on the results of these studies, shall we tell our blood group A patients to stay home 12 or tell everyone to take vitamin D or get vaccinated with BCG? What are the mechanisms underlying 13 these relationships? Although blood group antigens are known to play a role in infections, the results of 14 the recent GWAS study may have been influenced by the control group comprised of blood donors and 15 the lack of adjustment for comorbidities.

[5] Low vitamin D levels have often been associated with a 16 higher risk of infections, but vitamin D supplementation has not been shown to prevent respiratory 17 1 impact journals during the pandemic, but it is important to remember that correlation does not equal 2 causation. To further demonstrate our point, we studied the correlation between the global ranking of 3 the Fédération Internationale de Football Association (FIFA) and the ranking of COVID-19 cases by 4 country (Figure 1 

Hydroxychloroquine in patients with mainly mild to moderate coronavirus disease 2019: open label, 8 randomised controlled trial

Genomewide Association Study of Severe Covid-19

with Respiratory Failure

Letter: low population mortality from COVID-19 in 6 countries south of latitude 35 degrees North supports vitamin D as a factor determining severity-7 authors' reply

worldometer COVID-19 CORONAVIRUS PANDEMIC

Effect of Monthly High-Dose Vitamin D Supplementation on Acute Respiratory Infections in Older Adults: 12 A Randomized Controlled Trial

SARS-CoV-2 Rates in BCG-Vaccinated and Unvaccinated Young 14