In the spring, scientists throughout the world were actively discussing whether there is a connection between vaccination against tuberculosis in early childhood and the mild course of the new coronavirus disease. However, at that time, statistics on patients with COVID-19 were still insufficient to draw reliable conclusions. Medical doctors throughout the world are currently beginning to find important patterns that will help protect public
health in the future.
An analysis of statistical data was conducted by experts from St Petersburg University. It showed that the incidence of COVID-19, the course of acute interstitial pneumonia caused by infection, and the mortality rate from it are associated with being vaccinated with bacilli Calmette-Guerin (BCG) according to the national vaccination schedule. The mortality rate turned out to be lower in those countries and areas where national vaccine immunisation programmes have taken place for a long time or continue today, especially if revaccinations were practiced. These countries are Finland, China, Japan, Korea, and also countries in Eastern Europe, Central and South Asia, Africa, and the former USSR. This figures are significantly higher where large-scale BCG vaccination has never been practiced or stopped more than 20 years ago, for example, in the USA, Italy, the Netherlands, Belgium, and Germany excluding the lands of the former East Germany.
The authors of the paper are young researchers: Alina Petyaeva, a student at St Petersburg University and a laboratory assistant researcher; Iana Ivashkevich, a graduate of the online course of St Petersburg University in General Pathophysiology, who carries out research at the University; and a physician Liubov Kazacheuskaya. The article is written under the supervision of Leonid Churilov M.D., Ph.D., Deputy Head of the Laboratory of the Mosaic of Autoimmunity and Head of the Department of Pathology at St Petersburg University.
'BCG vaccine in Russia is given once in a lifetime for newborns,' said Iana Ivashkevich. 'But it is the early and long-term influence of the vaccine strain on the developing immune system that provides an adjuvant effect - it enhances the body's immune reaction to various antigens, including many infectious ones. An adjuvant is a substance that enhances immune responses in a non-specific manner. Many adjuvants also enhance autoimmune processes. But the BCG vaccine has properties that are uncharacteristic for most adjuvants: for example, it acts as an immune response-modulating agent, and also reduces the risk of some autoimmune diseases and lymphoid tumours. COVID-19 can cause autoimmune complications, so the properties of BCG, which are so unusual for an adjuvant, can be of benefit in this regard. According to statistics, in countries practicing neonatal BCG vaccination, there has been an overall decrease in infant mortality.
Revaccination is a renewed vaccination throughout life. For BCG It is now practiced by only four countries: Belarus, Kazakhstan, Turkmenistan, and Uzbekistan. It is important that the effect of trained immune system response is achieved if the BCG vaccine is given to an immature immune system, scientists are certain. 'There is reason to believe that in adults and elderly people who were not vaccinated in early childhood, the effect of late vaccine administration will be significantly less,' explained Leonid Churilov. 'At the same time, there are research papers by scientists from the Netherlands, where BCG is not given in childhood. They indicate that BCG administration to adults does not worsen, and, perhaps, somewhat attenuates the course of the disease when infected with the new coronavirus.'
As the authors of the article said, the BCG vaccine activates a local immune response on the mucous membranes. It is through them that acute respiratory disease caused by SARS-CoV-2 spreads. According to the scientists, the BCG vaccine serves as a trigger for a 'trained' immune system response that activates monocytes, macrophages and natural killer cells - that power in the non-antigen-specific protective rogrammes of the body. Also, gamma-interferon, produced after BCG vaccination, and other mediators may ultimately attenuate the course of COVID-19.
'The causative agent of the new coronavirus infection and BCG have common peptides, which means that induction of cross-immunity is possible. Large clinical trials of the BCG vaccine and trials of its use for the prevention of the new coronavirus infection are currently underway, for example, in the Netherlands and Australia,' said Iana Ivashkevich. Additionally, the scientists explain that the viewpoint on the connection of BCG vaccine with a decrease in the spread of COVID-19 and a less severe course of the disease is confirmed by studies of international research teams from the USA, Germany, Canada, India, and Iran.