A vaccination against tuberculosis appears to provide some protection against Covid-19 for people under 24 years of age, according to a new Israeli study.

The study, led by researcher Dr. Nadav Rappoport of Ben-Gurion University of the Negev together with colleagues from the Hebrew University of Jerusalem, found a correlation between countries’ policies for the Bacille Calmette-Guérin (BCG) vaccine against tuberculosis and those countries’ Covid-19 outcomes.

The protection appears to be significant primarily among those who received the vaccination in the last 15 years. The researchers did not find a similar effect among older adults who received the BCG vaccine longer than 15 years ago.

Their data revealed that BCG vaccination was consistently in the top two effects across 55 countries studied (comprising nearly 63 percent of the world’s population).

Rappaport, who is part of BGU’s department of software and information systems engineering, and his colleagues normalized the data so that countries were aligned by the first date at which each country reached a death rate of 0.5 deaths per million or higher. The researchers also controlled for demographic, economic, pandemic-restriction-related and health-related country-based variables. Only countries with a population of at least 3 million were included.

The research also compared how country-wide BCG vaccination compared with vaccinations for other diseases such as measles and rubella. Rappaport and his team found that other vaccines did not have a significant association with Covid-19 outcomes.

The Israeli research is not the first to find an effect of BCG beyond tuberculosis. Researchers in The Netherlands have reported that the vaccine appears to have a general stimulating effect on the immune system. The Netherlands study did not test BCG specifically for Covid-19 outcomes but shows a “cautiously positive picture” with a lower number of sick people in the period March-May 2020 among the vaccinated group as well as fewer fatigue complaints.

A separate American study suggests that, had BCG vaccination been mandatory several decades ago, the number of deaths in the first wave of Covid-19 in the United States could have decreased by as much as 80%.

BCG is the world’s most widely received vaccine. It is usually given shortly after birth or during early childhood.

“We propose that BCG immunization coverage, especially among the most recently vaccinated population, contributes to attenuation of the spread and severity of the Covid-19 pandemic,” the Israeli researchers concluded. “Our findings suggest that exploring BCG vaccine protocols in the context of the current pandemic could be worthwhile.”

The BGU research was published in the journal Vaccines.