How a tuberculosis vaccine may protect diabetics against Covid-19

Two years ago when the Covid-19 pandemic was overwhelming hospitals and morgues in dozens of countries, health practitioners in Pakistan made a strange observation: the mortality rate in Covid-related cases was much lower than the global average. 

Some experts were quick to point out that it could be because of the BCG vaccine, which is the first line of defence against tuberculosis, a disease rampant in the South Asian country. 

But that theory was never actually proven until, maybe, recently. 

A group of researchers at the Massachusetts General Hospital and Harvard Medical School have found evidence in clinical trials that the century-old vaccine could help protect those with type 1 diabetes against Covid-19.

The study, published in Cell Reports Medicine on Monday, evaluated the “safety and efficacy” of multi-dose Bacillus Calmette-Guerin (BCG) vaccine, primarily used against tuberculosis, in preventing coronavirus in at-risk and groups of people who haven’t received the Covid vaccine shots. 

The randomised trial — a controlled experiment — involved 144 participants. Researchers administered BCG vaccine to 96 people while 48 others received shots of placebo, which can be diluted water or anything other than the actual drug being tested. 

All the participants were type 1 diabetic patients. Diabetes UK, an organisation based in the United Kingdom fighting the disease, describes Type 1 diabetes as a serious condition where blood glucose, or sugar, level in the body gets too high, resulting in the body unable to make insulin.

The participants of the study were given three BCG or placebo vaccinations two years before the pandemic.

The study trial, which continued for 15 months with no drop-outs, found that multi-dose BCG vaccination was safe and the group which received it showed fewer confirmed cases of Covid-19 than the one who got placebo vaccination. 

Further breaking down the numbers in the study, researchers cite that one out of 96, or one percent, of the BCG-vaccinated group showed incidence of confirmed Covid-19 case, whereas six out of 48, or 12.5 percent, were infected with Covid in the placebo-administered group.

The researchers, however, pointed out that the criteria to confirm Covid-19 was developed ahead of the widespread availability of PCR testing, and took into account reporting of at least one FDA-defined symptom. 

The BCG-vaccinated group also showed resistance against other infections, the study found, suggesting that the vaccine could potentially be helpful in providing protection against evolving coronavirus variants.

In the study, the researchers highlighted that over the past 17 years, randomised clinical trials and epidemiology studies have shown that the BCG vaccine is effective in preventing a host of infections among humans, such as upper respiratory tract, leprosy, malaria, and several viral and bacterial infections.

Patients with type 1 diabetes are considered to be among the most vulnerable to Covid-19 and the researchers hope their findings could pave the way for a large-scale study looking into the effects of the BCG vaccine on them.

The UK's NHS recommends BCG vaccines for babies, children and adults under the age of 35 who are at risk of contracting tuberculosis, and advocates for the vaccine to be administered only once in a lifetime.

The vaccine, over a 100 years old, was developed to protect against tuberculosis, and considered to be the safest ever developed. An estimated three to four billion people in the world have already been vaccinated with BCG, while 120 million children get vaccinated every year.