After accounting for differences in factors that might affect vulnerability to the coronavirus - such as income, education, health services and age distribution - the scientists found countries with higher rates of Bacille Calmette-Guarin (BCG) vaccinations for tuberculosis had lower peak mortality rates from Covid-19.
A good example was Germany, which had different vaccine plans before East Germany and West Germany were unified in 1990, the researchers said. Covid-19 mortality rates among senior citizens are nearly three times higher in western Germany than in eastern Germany, where more older people received the vaccine as infants, they found.
The findings were reported on Thursday in the scientific journal Proceedings of the National Academy of Sciences.
Study co-author Luis Escobar of Virginia Tech said in a press statement BCG vaccines have been shown to protect against other viral respiratory illnesses. Dr Escobar cautioned the new findings are preliminary. The BCG vaccine is currently being tested for preventing Covid-19 in healthcare workers.
The study comes as more evidence is emerging that severe Covid-19 has lingering after-effects. Nearly 90 per cent of recovering Covid-19 patients discharged from a hospital in Rome were still not back to normal an average of two months after becoming ill, researchers said.
Doctors there studied 143 adults who had been hospitalised on average for two weeks. Most had been diagnosed with pneumonia, and one in five had needed help to breathe.
An average of 60 days after their first coronavirus symptoms, 87.4 per cent still reported at least one symptom - particularly fatigue and shortness of breath - and 55 per cent had three or more, researchers reported on Thursday in the Journal of the American Medical Association.
About one in four still had joint pain, and about one in five had chest pain. Roughly 44 per cent said their quality of life was worse now than before they got sick.
The researchers did not have information on patients' pre-COVID-19 medical problems and did not compare this relatively small group to patients discharged for other reasons. But they said their findings suggest more research is needed on the long-lasting effects of coronavirus infection.