A recent paper has been pre-published, albeit it has not yet been peer reviewed, that suggests correlations between tuberculosis (TB) vaccination policies and death rates due to COVID-19 (link). The conclusion is that it is possible that vaccination against TB may confer some protective properties against COVID-19 infection. Its findings are interesting.
It has been known for some time that the TB vaccines, Bacillus-Calmette-Guerin (BCG), confer some heterologous immune effects. This means that it can boost or stimulate the immune system to protect against infections other than the specific disease it was designed for. BCG has been shown to allow the immune system to fight a range of respiratory infections and sepsis, caused by both microbial and viral sources (link). It follows that the authors trained their minds to look at its possible effectiveness within the context of the epidemiology of the the COVID-19 pandemic.
The reaction in the wider science media has been rather subdued, in contrast to elements of the general media, where the reaction has been a little more shrill. Scientists have been largely cool on the findings, for the simple reason that the paper being not yet peer reviewed (it is going through this process at present) means that its findings are not officially accepted, its methodology un-assessed. Other factors that have made scientists wary are the many factors in the mix when it comes to reading and interpreting the reported data. Also it is crucial to remember that BCG is not clinically proven to protect against COVID-19. And lastly, the results vary depending on how you look at the data.
It’s a remarkably simple paper, using publicly and easily available data, and using rather straight forward statistical analysis. It presents evidence that countries with extremely high mortality rates such as Iran (6.19%), Italy (12.33%), USA (2.5%), Spain (9.4%) (link) are also countries with no long standing (or non-existent) TB vaccination policies. If some of those stats seem low, then look at them beside the average death rate in other countries, which can be as low as 0.96% (Thailand), 1.4% (Germany).
It is important to note that the rates I gave above (taken from the WHO website) are based on deaths per total infected numbers. The total recorded/reported infected number in any nation does not currently reflect reality as no country has a method to detect every infected individual. Instead, the paper deals with deaths per population numbers in total, which gives a better reflection of COVID-19 related mortality. That method in itself is dependent on nations to accurately report COVID-19 related deaths. There are questions raised within most countries about their COVID-19 reporting reliability and the classification of deaths, but there are actually currently particular concerns about under reporting of COVID-19 related deaths in Thailand, Germany and China, among others.
The deaths world wide are mostly among the over 65 demographic (link), with obvious exceptions (link)the young are not immune to COVID-19 fatalities. But it suggests that the earlier a country practiced TB vaccination policies as part of public health initiatives, the more the aged population can weather COVID-19 infection. Iran only began TB vaccinations for all children only in 1984, leaving its elderly population possibly vulnerable. Italy never had a consistent policy of TB vaccination, neither does The USA (2.5% mortality rate) and The Netherlands (9.9% mortality rate). Spain only started compulsory TB vaccinations in 1965, which may have left a vulnerable elderly population at risk of high COVID-19 fatality rates; as mentioned, their mortality rate is a 9.4%. In contrast, Denmark began widespread vaccinations in 1946 and has thus far only recorded 141 death. However, their mortality rate per total infected is 3.9%, but with a low recorded infection rate (4077 as of 5 April 2020). Translated into COVID-19 deaths per million of population, the paper reports Spain as experiencing 29.5 deaths per million, while Denmark has 2.3 deaths per million. That is according to this paper, released on 30th March, 1 week ago today. The numbers have since changed. Other sources suggest much higher figures for COVID-19 deaths per million, such as the European Centre for Disease Control. On 6 April 2020 it gives Spain as having 265.5 deaths per million, Denmark as 30.9, and Italy as 262, and the USA as having 29.4 (link). But the trends are similar, although clearly the authors may have to update their paper before publication.
However, the TB vaccination history of a country does not explain a lot of COVID-19 questions, and neither do the authors suggest this. Actually among nations with similar long standing TB policies the death rates are strikingly varied. Germany for instance has a high infection rate of COVID 19 with 91,714 cases to date, but as of 5 April 2020 only recorded 1342 deaths (link), or 17.2 deaths per million (link). Germans however have a similar vaccination history to Spain – German BCG-TB vaccinations began in 1961 and ended in 1998 (link). France has so far less cases recorded at 67757, but has recorded 7546 deaths, or a huge 123.76 deaths per million by 5 April 2020. Strikingly, they began compulsory vaccinations in 1950 and ended the policy in 2008.
There are many issues that may play a part in the development of the infection/death rate data. The huge variability in the ability of individual countries to test, detect, isolate and medically treat identified cases being the most obvious. The ability or willingness of countries to enforce disease reducing measures (social distancing, prosecution of those accused of infringement etc) and truthfully report cases is also based on a wide range of cultural, political and sociological factors. The state of public health care systems (quality of hospitals, medical care etc) is also hugely varied and will hugely influence survival rates among the infected. Additionally,, there are an enormous range of possible demographic reasons for the variability, such as general health of the population, the lifestyles of those who are most at risk of death (drug users, smokers, fatty diets etc). Another factor is the unknown numbers of people with undetected underlying health conditions that may make them more susceptible to more severe COVID-19 infections.
It is all something to think about. If you are vaccinated against TB, you may have a milder dose of COVID-19 infection. Or you may not. All in all, the risks seem unchanged. The older you are, the more dangerous the disease is to you. If you have underlying health conditions, particularly heart and lung conditions, then it is even more so. If you are young and under 45 and reasonably fit, you may be ok. If you are any of these and you get infected in Yemen, you may be in big trouble. If you get infected in Germany, you may be ok. But you also may not be, it depends…….