BCG vaccination policy and preventive chloroquine usage: do they have an impact
on COVID-19 pandemic?
https://www.nature.com/articles/s41419-020-2720-9
Published: 08 July 2020
Abstract
Coronavirus disease 2019 (COVID-19) is a severe acute respiratory syndrome cause
d by Coronavirus 2 (SARS-CoV-2). In the light of its rapid global spreading, on
11 March 2020, the World Health Organization has declared it a pandemic. Interes
tingly, the global spreading of the disease is not uniform, but has so far left
some countries relatively less affected. The reason(s) for this anomalous behavi
or are not fully understood, but distinct hypotheses have been proposed. Here we
discuss the plausibility of two of them: the universal vaccination with Bacillu
s Calmette–Guerin (BCG) and the widespread use of the antimalarial drug chloroq
uine (CQ). Both have been amply discussed in the recent literature with positive
and negative conclusions: we felt that a comprehensive presentation of the data
available on them would be useful. The analysis of data for countries with over
1000 reported COVID-19 cases has shown that the incidence and mortality were hi
gher in countries in which BCG vaccination is either absent or has been disconti
nued, as compared with the countries with universal vaccination. We have perform
ed a similar analysis of the data available for CQ, a widely used drug in the Af
rican continent and in other countries in which malaria is endemic; we discuss i
t here because CQ has been used as the drug to treat COVID-19 patients. Several
African countries no longer recommend it officially for the fight against malari
a, due to the development of resistance to Plasmodium, but its use across the co
ntinent is still diffuse. Taken together, the data in the literature have led to
the suggestion of a possible inverse correlation between BCG immunization and C
OVID-19 disease incidence and severity.
Conclusions
In this study, we have presented the evidence available in the literature that h
as led to the suggestion of the possible effects of two factors, BCG vaccination
and exposure to CQ, on the susceptibility to the COVID-19 infection. BCG vaccin
ation is known to operate through the cell-mediated immunity that is important a
gainst COVID-1948. Although originally intended for tuberculosis, BCG immunizati
on does not provide satisfactory results for the adult pulmonary disease, but co
nfers partial protection against various other diseases49. We have presented the
data, suggesting that the BCG immunization correlates with lower incidence and
gravity of the COVID-19 disease across different countries, even when the BCG im
munization was performed in childhood. Although the matter of CQ and HCQ does no
t have the degree of numerical sophistication of BCG vaccination, it still deser
ves to be considered. Unfortunately, the literature on CQ and HCQ has so far exc
lusively dealt with their therapeutic role in patients affected by the COVID-19
infection, frequently in its advanced stages. In this contribution, we have inst
ead emphasized the possible chemoprophylactic role of CQ and HCQ: even if the ev
idence for it is admittedly only circumstantial, such a role should be tested in
appropriately designed trials
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