Public trust in vaccine safety is slowly growing in Europe even as it dips in parts of Asia and Africa, researchers said Friday, calling for more investment in health information campaigns for the forthcoming Covid-19 vaccine.

The largest ever global survey of vaccine confidence, published in the Lancet medical journal, shows clear links between political instability and misinformation and the levels of trust in the safety of medicines.

The World Health Organization lists vaccine hesitancy as one of its top 10 global health threats, and dipping levels of immunisation coverage have seen outbreaks of preventable diseases such as polio and measles in recent years.

The survey of nearly 300,000 respondents shows trust in vaccine safety increasing -- with some exceptions -- across Europe. 

In France, where confidence in vaccines has been consistently low for decades, it shows an increase from 22 percent to 30 percent of people strongly agreeing they are safe.

In Britain, confidence in vaccine safety rose from 47 percent in May 2018 to 52 percent in November 2019.

Poland and Serbia however saw significant declines in public vaccine confidence. 

Afghanistan, the Philippines, Indonesia, Nigeria and Pakistan saw "substantial" increases in the number of people strongly disagreeing that vaccines are safe between 2015 and 2019.

In Azerbaijan, public mistrust surged from 2 percent to 17 percent in that timeframe.

Authors of the research attributed this "worrying trend" in part to political instability and religious extremism.

Heidi Larson from the London school of Hygiene and Tropical Medicine, who led the research, said online misinformation was also a significant problem. 

"When there is a large drop in vaccination coverage, it is often because there's an unproven vaccine safety scare seeding doubt and distrust," she said. 

Larson said that public mistrust in politicians in general also likely played a role. 

As the world races to find a vaccine to potentially end the Covid-19 pandemic, the researchers warned that governments need to ramp up investment in public information campaigns and as well as distribution infrastructure. 

Without this, Daniel Salmon from John Hopkins Bloomberg School of Public Health said "there is a risk of SARS-CoV-2 vaccines never reaching their potential due to a continued inability to quickly and effectively respond to public vaccine safety concerns, real or otherwise".