The World Health Organisation has played down studies suggesting that that the BCG vaccine may provide protection against Covid-19 and significantly reduce death rates in countries - including Ireland - where there are high levels of vaccination.
The vaccine is used to prevent tuberculosis and was given to children in Ireland up to 2015.
A wide-ranging study by an Irish medical consultant working with epidemiologists at the University of Texas in Houston published last week found that countries with vaccination programmes had fewer coronavirus cases by a factor of 10 when compared to countries where BCG programmes are no longer deployed.
This translates into a death rate up to 20-times less, according to urologist Paul Hegarty of the Mater Hospital, Dublin.
The Houston study was largely statistical and came with caveats because of possibility of confounding factors. To reduce the possibility of error, the researchers re-evaluated cases during the course of the pandemic and made country-by-country comparisons including between Ireland and the UK, Mr Hegarty said.
“We did not expect to see such a marked difference,” he said.
“Over the 15 days, incidence of Covid-19 was 38 per million in countries with BCG vaccination whereas the incidence of Covid-19 was 358 per million in the absence of such a programme. The death rate was 4.28 per million in countries with BCG programmes and 40 per million in countries without such a programme.”
However the WHO scientific briefing paper urges caution and says there “is no evidence that the BCG vaccine protects people against infection with Covid-19”.
The note says two clinical trials addressing this question are underway and says it will evaluate the evidence when available.
“In the absence of evidence, WHO does not recommend BCG vaccination for the prevention of Covid-19.”
It said there was “experimental evidence from both animal and human studies that the BCG vaccine has non-specific effects on the immune system”.
“These effects have not been well characterised and their clinical relevance is unknown.”
‘Ecological studies’
WHO has also updated its ongoing evidence review of the major scientific databases and that update yielded three manuscripts posted online before peer-review in which the authors compared the incidence of Covid-19 cases in countries where the BCG vaccine is used with countries where it is not used and observed that countries that routinely used the vaccine had less reported cases of Covid-19 to date.
“Such ecological studies are prone to significant bias from many confounders, including differences in national demographics and disease burden, testing rates for Covid-19 virus infections, and the stage of the pandemic in each country,” the WHO scientific assessment said.
The WHO review also noted two registered protocols for clinical trials, both of which aim to study the effects of BCG vaccination given to health care workers directly involved in the care of patients with Covid-19.
Scientists in Melbourne, Australia have started administering BCG vaccine or a placebo to thousands of healthcare workers while a clinical trial of 1,000 healthcare workers started recently in the Netherlands, with results within three to six months.
The WHO paper pointed out that BCG prevents severe forms of tuberculosis in children and warned that “diversion of local supplies may result in neonates not being vaccinated, resulting in an increase of disease and deaths from tuberculosis.
It said that in the absence of evidence, WHO does not recommend BCG vaccination for the prevention of Covid-19.
