It’s been fewer than six months since a novel coronavirus was discovered and this disease known as Covid-19 has since taken the world by storm affecting 185 countries, infecting close to 2.5 million people and killing more than 160,000 as of April 20, 2020. In South Africa, the number of confirmed cases surpassed 3000 with more than 50 deaths being reported.
Around the world, teams from various countries are racing to discover a targeted vaccine – the quintessential silver bullet – against this Covid-19, but none seem to be evidently available in the immediate term. Accordingly, other teams of researchers around the globe are looking for alternative and existing vaccines as a stop-gap protection against Covid-19 until such vaccine and antiviral medications are available.
An epidemiological study by Dr Gonzalo Otazu from the New York Institute of Technology and his team reported that countries that routinely vaccinate newborns with the Bacillus Calmette–Guérin (BCG) vaccine have reported fewer Covid-19 confirmed cases and deaths than countries which either have discontinued or never implemented a universal BCG vaccine policy. In South Africa, where BCG vaccines for infants is routinely required, 1.6 per cent of confirmed coronavirus cases have ended in death whereas that figure is significantly higher in more developed Western countries that do not have universal BCG vaccination policies. For example, an estimated 5, 13, and 11 per cent in the United States, Italy and Netherlands, respectively. While correlation does not imply causation, it seems that this assessment may not be without merit on a deeper analysis.
BCG is a widely administered vaccine containing a live and weakened bacterium (Mycobacterium bovis). Introduced in 1921, this vaccine offers a cost-effective and safe measure against Tuberculosis (TB) – a bacteria that causes lung infection – and remains widely used in developing countries where TB is still prevalent. Unlike conventional vaccines that elicit specific responses aimed at a specific disease, scientific studies have suggested that the BCG vaccine has the so-called “off-target effects”, meaning that it can stimulate broader and long-lasting responses against diseases other than the one it was intended for. Once a pathogen succeeds in crossing the anatomical and physiological barriers in our lungs, for example, our first line of defence against this pathogen is our innate immunity (also known as general or nonspecific immunity) which immediately takes over to efficiently remove it in order to prevent the spread and movement of the pathogen throughout our body.
The BCG vaccine does not directly protect against the intruding Covid-19, but instead provides a boost to the immune system which may effectively lead to a milder infection and symptoms experienced by the host. More specifically, it has been suggested that the BCG vaccine may elicit a state of enhanced immune activation that is based on a memory-like response termed “trained innate immunity”, initiating a faster and stronger immune response against a pathogen; the perceived significance of this response is that it essentially “buys” time until the more complex and slower adaptive immunity (also known as our acquired or specific immunity) becomes activated.
The basis of these effects of “trained innate immunity” is still relatively new and not well characterised. In addition, the clinical relevance of how it may confer long-lasting protection in the early stages of infection is also not yet completely understood. Accordingly, the only way to really test whether the childhood BCG vaccine is effective against Covid-19, especially in adults and the elderly that are more vulnerable to the disease, is to carry out clinical trials. Until the results from such studies are released, it has been said that a cautious view should be taken due to the fact that the BCG vaccine does not act like other vaccines and epidemiological studies such as that conducted by Dr Otazu does not take into account the many confounders when comparing various countries, including differences: in population demographics and concurrent disease burdens, rate of testing for Covid-19 virus as well as the timing and extent of which national restrictions were implemented.
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