BCG vaccination may be protective against Covid-19
Paul K. Hegarty, Ashish Kamat, Helen Zafirakis, Andrew DiNardo
Background Covid-19 virus has infected over 300,000 people and led to over 13,000 deaths
in its first 3 months; yet the pattern of development is not uniform.. Mechanistic evidence
exists to suggest that vaccination with Bacillus Calmette-Guérin (BCG), can have protective
effects against viral infection. Herein we examine whether national programs which use
BCG vaccination with the aim of reducing tuberculosis infections could account for the
differential incidence and mortality observed in Covid-19 between various countries.
Methods We accessed and collated data from three sources - accessed on March 24th 2020
- for the analysis: The European Centre for Disease Prevention and Control for the number
of cases and deaths attributed to Covid-19; The World Atlas of BCG for list of countries
describing programs of BCG vaccination; and Worldometer.info for the population of all
Findings 178 countries had data from all three sources and formed the basis of our analysis.
Current national programs of BCG vaccination exist in 131 countries; 21 countries have no
current program of national BCG vaccination; and for 26 countries status is unknown. Over
preceding 15 days, incidence of Covid-19 was 38.4 per million in countries with BCG
vaccination compared to 358.4 per million in the absence of such a program. The death rate
was 4.28/million in countries with BCG programs compared to 40/million in countries
without such a program.
Interpretation Countries with national program of whole population BCG vaccination
appear to have a lower incidence and death rate from Covid-19. This may be due to the
known immunological benefits of BCG vaccination. In the absence of a specific vaccination
against Covid-19, population-based BCG vaccination may have a role in reducing the impact
of this disease and is being studied in a prospective trial.
Word count: 802 (limit 3,500)
References: 25 (limit 30)
BCG vaccination may be protective against Covid-19
To date, in 3 months, coronavirus pandemic has infected more than 480,000 individuals
and caused over 13,000 deaths. Based on transmission in China and initial transmission in
Europe, the pandemic is expected to peak in June or July1, 2. To try and limit its spread,
stringent public health measures are being implemented to slow the spread and protect
those most vulnerable. Governments and communities are implementing social distancing
and quarantining those with disease to minimize spread.. A coronavirus vaccine is expected
to take a minimum of 12 to 18 months to develop. In the meantime, repurposing existing
and safe vaccines that induce non-specific immune benefits may be an additional tool3.
There is strong epidemiologic evidence that live, attenuated vaccines induce non-specific
mortality benefits. For example, Bacillus Calmette-Guérin (BCG), a live attenuated strain of
Mycobacterium bovis, the most commonly administered vaccine worldwide, induces an
~38-45% mortality reduction4, 5. Developed to combat tuberculosis (TB), the mortality
benefit from BCG is not TB-specific, but due to a decrease in neonatal sepsis and respiratory
tract infections6. Not limited to neonates and children, BCG vaccinated elderly (age 60-75)
individuals experience decreased respiratory infections7. For bladder cancer, intravesicular
BCG boosts host immunity, reduces tumor recurrence progression and decreases mortality
and has been approved for use in bladder cancer since the 1990s8.
The non-specific immune benefits of BCG have been known since the 1970s when BCG was
shown to improve immunity against listeria and influenza in murine models9, 10. More
recently, studies have demonstrated that the molecular mechanisms of the non-specific
benefits of BCG are due to NOD2 and mTOR mediated changes in the epigenetic landscape
of immune cells11-14. When medical students were vaccinated with BCG, 3 months later they
demonstrated improved immunity to Staphylococcus aureus and Candida12. The BCG
priming induces persistent chromatin conformational changes in innate and adaptive
immune cells that improves anti-mycobacterial, bacterial, fungal and viral immunity11, 12, 14-
18. BCG vaccinated healthy controls re-challenged with yellow fever virus demonstrated
improved anti-viral immunity and decreased viral loads. After BCG vaccination, the
epigenetic-mediated non-specific immune benefits last at least a year14. Therefore, while a
coronavirus-specific vaccine is being developed , there exists sufficient data to support
evaluating BCG vaccination as a means to prime host immunity and mitigate the current
To identify whether BCG vaccination does confer some natural protection, we decided to
evaluate the incidence and mortality patterns from Covid-19 with BCG vaccination
programs. When we looked at Europe, the current epicentre of the outbreak, we found
that the map of countries most affected in Europe bears striking resemblance to the map of
countries that do not have national programs of BCG vaccination (Fig 1).
Figure 1a, A - Country with current universal BCG program of vaccination; B – Country no
longer has BCG vaccination program; C – Country never had BCG vaccination program. Data
courtesy of the BCG World Atlas4.
Figure 1b. Screenshot of heatmap of SARS-CoV-2 cases in Europe ECDC website2 , accessed
March 24 2020.
To look at this further we collated all reported cases and fatalities of Covid-19 world-wide
from the European Centre for Disease Prevention and Control on the previous 15 days, on
March 24nd 202017. The per million incidence and fatality was then calculated using the
population numbers in 2020 as recorded on Worldometers.info18. Finally we collated the
countries that have programs of whole population vaccination still in place, as reported on
the World Atlas of BCG19.
Over the 15 day period from 9 March to 24 March 2020, the incidence of Covid-19 was 80
per million population, with a fatality of 0.55 per million. A total of 178 countries were in
the database: current national programs of BCG vaccination exist in 131 countries; 21
countries have no current program of national BCG vaccination; and for 26 countries status
is unknown. When we dichotomised the data according to those countries with and without
BCG programs, the incidence of Covid-19 was 38.4 per million in countries with BCG
vaccination whereas the incidence of Covid-19 was 358.4 per million in the absence of such
a program. Likewise, the fatality recorded in countries with BCG programs was 4.28/million,
compared to 40/million in countries without a national program. Calculating a crude case
fatality rate (CFR) by dividing deaths by cases, countries with a BCG program the CFR was
0.13% and 0.33% in countries without a BCG program. Countries that have a booster
injection of BCG 7 to 14 years later had no better outcomes than those with a single
We recognize that these data are observational and based on a single time-point and that
there may be are several confounding issues such as limited testing and reporting in many
countries. However as these data are derived from 178 countries the trend is striking and
supports the mechanistic data that exists for BCG as a protective agent not only for viral and
other infections but also against cancer.
There are currently efforts under way to initiate a randomised, blinded, placebo-controlled
trial3. This would offer a low risk, high benefit proposition. BCG has been used for close to a
century and three billion doses have since been administered since it was developed in
192219 with a remarkable long-standing safety record. For individuals previously vaccinated,
recent studies have demonstrated revaccination is safe, well-tolerated and not associated
with an increased frequency or severity of local or systemic reactions than the primary BCG
vaccination20-24. While awaiting a coronavirus-specific vaccine, using an existing, available
and safe vaccine such as BCG to boost host immunity may represent an important tool
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