Reconcile the debate over protective effects of BCG vaccine against COVID-19

Abstract

While awaiting the COVID-19 vaccines, researchers have been actively exploring the effectiveness of existing vaccines against the new virus, among which the BCG vaccine (Bacillus Calmette-Guérin) receives the most attention. While many reports suggest a potential role for BCG immunization in ameliorating SARS-CoV-2 infection, these findings remain controversial. With country-level COVID-19 outbreak data from Johns Hopkins University Coronavirus Resource Center, and BCG program data from World Atlas of BCG Policies and Practices and WHO/UNICE, we estimated a dynamic model to investigate the effect of BCG vaccination across time during the pandemic. Our results reconcile these varying reports regarding protection by BCG against COVID-19 in a variety of clinical scenarios and model specifications. We observe a notable protective effect of the BCG vaccine during the early stage of the pandemic. However, we do not see any strong evidence for protection during the later stages. We also see that a higher proportion of vaccinated young population may confer some level of communal protection against the virus in the early pandemic period, even when the proportion of vaccination in the older population is low. Our results highlight that while BCG may offer some protection against COVID-19, we should be cautious in interpreting the estimated effectiveness as it may vary over time and depend on the age structure of the vaccinated population.

Country-level factors dynamics and ABO/Rh blood groups contribution to COVID-19 mortality

“…As an example, vaccination against Bacillus Calmette-Guerin (BCG) has been recently reported as protective against severe COVID-19 infection 22 , 66 – 68 . However, a recent work has reported that, similarly with several determinants we investigated, BCG vaccination exerted a strong protective effect against COVID-19 in the early stage of the pandemic while fading in later stages 23 . Finally, we investigated only the ABO and Rhesus blood groups amongst many genetic loci that have been recently identified in genome wide association studies (GWAS) 14 , 19 , or more focused approaches 11 , 12 , 14 , 38 .…”

The Global Interest in Vaccines and Its Prediction and Perspectives in the Era of COVID-19. Real-Time Surveillance Using Google Trends

“…However, overall interest in the BCG vaccine has remained unchanged. According to Fu et al [7], the BCG may offer some protection against COVID-19; however, it may differ over time, depend on the age structure, and vary in different populations. The viral pathogens often cause respiratory tract infections in children.…”

“…Before the COVID-19 vaccines were released, the effectiveness of existing vaccines against the new virus was actively explored, with the BCG vaccine receiving special consideration [7]. The inquiry in question was whether or not the BCG vaccination could protect against COVID-19 or at least reduce the severity of the disease.…”

100 years of Bacillus Calmette–Guérin immunotherapy: from cattle to COVID-19

“…A 2021 study has attempted to reconcile the conflicting findings from different studies regarding protection of BCG against COVID-19 (ref. 155 ). By modelling the effect of BCG vaccination across different times during the pandemic the authors show that the protective effect of BCG vaccination against COVID-19 is strongest during the early stages of the pandemic.…”