Doctor’s Note: Coronavirus and the tuberculosis vaccine

A study found countries with widespread BCG vaccination had fewer deaths from coronavirus. But are the results reliable?

[Media Raw Stock/Getty Images]
[Media Raw Stock/Getty Images]

The novel coronavirus has infected nearly 2.5 million people around the globe and it continues to spread like wildfire. Currently, there is no proven cure for COVID-19 – the disease caused by the virus – or vaccine against it.

Despite this, news that the Bacillus Calmette-Guerin (BCG) vaccination might offer protection against coronavirus has been doing the rounds. This has come from the findings of a study – not yet peer-reviewed or scrutinised – which has established a geographical link between the BCG vaccine and reduced mortality from the coronavirus.

This news has taken the internet by storm and has appeared as a ray of hope in the race to beat COVID-19. Having received the BCG vaccine as a child, I wondered if the gunshot-wound-like scar on my right upper arm really is an assurance against COVID-19.

The deeper I probed, however, the more sceptical I became. The bottom line is, this study has several limitations and the results need to be interpreted with caution.

BCG vaccine, past and present

The BCG vaccine against tuberculosis (TB) was developed by two French researchers, Albert Calmette and Camille Guerin. It was first administered to humans in 1921, to a newborn baby who was born to a TB-infected mother and raised by a TB-infected guardian (the grandmother).

The baby never developed TB, even though it is a highly infectious disease. Today, the BCG vaccine is mandatory in almost all countries in Africa, Asia and South America and is given to more than 100 million newborns each year.

Intradermal injection – an injection into the middle layer of the skin (dermis) – is the most common route of administration, given in one of the upper arms during the first month of life. In most people, it leaves a small scar.

This vaccine has been consistently shown to be highly effective in preventing severe forms of TB in children, with an overall protective efficacy of 86 percent. This means that people vaccinated with the BCG are 86 percent less likely to be infected with TB than those who are unvaccinated.

The BCG vaccine is also thought to enhance general immunity and has exhibited “non-targeted” effects, which effectively means it has other beneficial effects as well as protecting against TB. The reason for this is not fully understood, but the vaccine is associated with the reduction of overall mortality by about 50 percent in vaccinated children below the age of five.

There are also some published reports of its beneficial effects in non-TB respiratory infections, allergies, eczema and asthma, although overall results of studies are so far inconclusive. In addition to protecting against TB, it also works against leprosy.

The pressing question right now is, is this miracle TB vaccine miraculous enough to fight COVID-19?

For starters, TB is caused by a bacterium while a virus is the causative agent in COVID-19. One may argue that the vaccine could work through a “non-targeted” effect but so far, the evidence is too weak and misleading to establish any credibility.

BCG vaccine and coronavirus

The new report which has linked BCG vaccination policy with general protection against COVID-19 has appeared in more than 80 news reports around the world and has been tweeted more than 7,000 times.

However, this study has several shortcomings and, therefore, its results should be interpreted with caution.

The research is an ecological study in which the population is defined geographically. It fails to take several factors into account, including heterogeneity of population, vaccination rates and the difference in response rate among individuals.

To give readers some perspective, a strongly criticised ecological study published in 2012 found a positive correlation between a country’s chocolate intake per capita and its number of Nobel Prize winners.

Dr Christopher Labos, a researcher at McGill University in Canada, wrote about that report: “The problem with country-level data is that countries don’t eat chocolate, and countries don’t win Nobel prizes. People eat chocolate, and people win Nobel prizes.”

The same goes for this BCG-COVID-19 study. Even if we agree that this study is flawless, it is still only a correlation study which does not establish causality.

Continuing with the previous example, all people who eat chocolate do not win a Nobel Prize. Similarly, in the context of this study’s results, all people who are vaccinated with BCG may not have protection against COVID-19.

The fact that not enough research has yet been carried out on the coronavirus further undermines the conclusions drawn from this research.

In fact, there is no evidence of a scientific link between the BCG vaccination and protection for individuals against the coronavirus.

Experts at the University of Goettingen in Germany estimate that, up until March 30, only about 9 percent of COVID-19 cases had been detected, based on data from 40 of the most affected countries.

Moreover, publicly available data on COVID-19 reflects the number of deaths occurring in healthcare facilities, but not the deaths at private homes and nursing homes, as confirmed by an Italian official. In the absence of the correct figures, the results of a population-level study cannot be fully trusted.

Lastly, a very crucial limitation of this research study is the stage of the pandemic when data was retrieved for analysis.

This study obtained data regarding COVID-19 cases and deaths on March 21, 2020. As the pandemic progressed after that date, many countries experienced a significant increase in death rates.

In the United States, the first death due to COVID-19 was reported on February 29 and by March 21, the number of deaths in total had reached 301. Alarmingly, there was a drastic change in the number of deaths in the next three weeks, with 22,105 deaths recorded by April 12 and more than 40,000 by April 19.

Because the numbers are changing so fast, the study results lack reliability.

Another ecological study (which has also not yet been peer-reviewed) that used COVID-19 statistics from April 3, 2020, found no correlation between the BCG vaccination policy of a country and protection against COVID-19.

After reviewing the available evidence, the WHO published a scientific brief on April 12, stating: “There is no evidence that the Bacille Calmette-Guérin vaccine (BCG) protects people against infection with COVID-19 virus. In the absence of evidence, WHO does not recommend BCG vaccination for the prevention of COVID-19.”

What now?

Two randomised, controlled trials (the gold standard study design) – one in Australia and the other in the Netherlands – are being carried out to examine the effects of BCG vaccination on protection against COVID-19 among healthcare workers, the front-line heroes of the current pandemic. The results of these clinical trials are expected to provide better evidence of any association.

Until we have robust evidence about the best ways to control this pandemic, it is only logical to take the preventive measures recommended by the WHO seriously.

These include social distancing, frequent handwashing, practising good respiratory hygiene (for example wearing a mask if necessary), seeking early medical help if you develop symptoms, including a fever and a cough, or you have difficulty breathing, and avoiding touching your face.

In these difficult times, research studies must be interpreted with caution, especially by the policymakers and the media.

While rapid dissemination of new preventive and treatment strategies is essential, spreading misinformation is detrimental to our fight against the COVID-19 crisis – in this case by potentially giving a false sense of immunity to a big chunk of the population.

Source: Al Jazeera

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