COVID-19: Could TB Vaccine Offer Protection?
Currently, there are no drugs that can prevent COVID-19, and there is no vaccine. As the virus traverses the globe, scientists are working at breakneck speed to identify ways to slow or stop the disease.
Taking a new drug from initial trials through to the clinic stage is an incredibly long process. Therefore, researchers are keen to identify vaccines that are already in use that might help tackle SARS-CoV-2.
If scientists have already demonstrated that a vaccine is safe in humans, the journey from clinical trial to widespread use is comparatively short.
Recently, researchers from the Murdoch Children’s Research Institute in Australia (MCRI) began organizing a trial to investigate whether the tuberculosis (TB) vaccine known as the bacille Calmette-Guerin (BCG) might offer some protection against COVID-19.
The researchers plan to trial the vaccine on around 4,000 front line medical staff at hospitals across Australia.
Project lead Nigel Curtis from the MCRI explains that they hope to “see a reduction in the prevalence and severity of COVID-19 symptoms in healthcare workers receiving the BCG vaccination.”
What is the BCG vaccination?
The BCG vaccine protects against TB, an infectious disease that most commonly affects the lungs. A bacterium called Mycobacterium tuberculosis is what causes TB.
The BCGvaccine reduces the chances of the bacterium infecting someone. It also reduces the severity of the disease in those who do contract it.
The BCG vaccine first became available in 1921, and it appears on the World Health Organization (WHO) List of Essential Medicines. In excess of 100 million babies receive the BCG vaccination each year.
Aside from TB, the BCG vaccine also protects against other conditions that involve mycobacterium, including leprosy. Scientists produce the vaccine using live Mycobacterium bovis taken from bovines, which they have attenuated to reduce their virility.
Why might BCG work against COVID-19?
Researchers are keen to investigate the BCG vaccine against COVID-19 because earlier work has shown that it might reduce the risk of some respiratory infections that are entirely unrelated to TB.
For instance, a study that scientists conducted in Guinea-Bissau concluded that “BCG vaccination may have a non-targeted protective effect against [acute lower respiratory tract infection], the effect being most marked in girls.”
In another study, researchers delved into retrospective data from Spanish hospitals. They concluded that “BCG vaccination at birth may decrease hospitalization due to [respiratory infection] and sepsis.” Similarly, a study carried out in Brazil found an association between BCG immunization and a reduced risk of pneumonia mortality in children.
It is still not clear exactly how and why these so-called heterologous effects of the BCG vaccine occur. However, it appears to be due to a nonspecific boosting of the immune response.
Although no studies, to date, have investigated the BCG vaccine’s influence over SARS-CoV-2, the scientists hope that the story might be similar. If the BCG vaccine can bolster the immune system, it might reduce the infection rates of SARS-CoV-2 or lessen the severity of COVID-19.
Prof. Kathryn North, director of MCRI, says, “The federal and state health departments, together with Australian and international philanthropists, have shown a willingness and capacity to step up to fund a number of COVID-19 related trials.”
She continues, “Using rapidly sourced and immediately deployable funds, we will be relentless in our pursuit of prevention's and treatments for this unprecedented pandemic. These trials will allow the rapid advancement of the most promising candidates to clinical practice, giving us the most number of shots on goal against COVID-19 as possible.”
The researchers do not expect the BCG vaccination to be a cure or a perfect method of prevention. However, the vaccine might offer an extra round of defense if people can use it alongside the protective equipment they apply in healthcare settings.