Proportion of vaccine-related reports categorised as positive or neutral, by country.

A surveillance tool developed by an international team of researchers can track anti-vaccination sentiment online, allowing them to respond to vaccine concerns as they emerge.

Researchers have been monitoring 144 countries using the tool, in the hope public health officials can respond quickly to a loss of confidence in vaccines before vaccination refusal and disease outbreak occur.

The research, released Online First in The Lancet Infectious Diseases on Monday, found there were 10,380 reports on vaccines between May 2011 and April 2012. Nearly 70 per cent of the reports were positive or neutral towards vaccination, while just over 30 per cent were negative.

Of the negative reports, almost half were associated with vaccine suspension and refusal, belief systems that opposed vaccination, and risk perceptions.

Lead author of the study, Heidi Larson, said she was prompted to develop the tool while working for UNICEF's global immunisation program.

"[I] saw a growing number of countries facing negative media and public questioning of vaccines, the most significant of which was the northern Nigeria boycott of polio vaccination for 11 months from mid-2003," Dr Larson, from the London School of Hygiene & Tropical Medicine in the UK.

"I realised that there was no systematic monitoring nor assessment of the emergence of public concerns about vaccines, and thought there was a great need for this type of surveillance."

The tool is so sophisticated that it can evaluate and prioritise reports according to their potential to disrupt vaccine uptake. It works by monitoring online media, such as blogs, based on a set of search criteria. Characteristics of the report are identified including the vaccine, disease, date and location, before being forward to analysts. If a negative report is categorised it as “high alert,” the information could then be forwarded to the Ministry of Health, World Health Organisation and research institutes in the country affected, Dr Larson said.

She believes overall distrust in vaccines is increasing and is being more publicised through online mediums. There were a number of reasons for negative views, she said, including stories about bad reactions after immunisation, alternative belief systems, including belief in naturopathy, and distrust in governments and health care providers.

The surveillance tool would now be expanded to detect reports in additional languages, Dr Larson said.

"This is a system which aims to understand the range of sentiments and nature of issues about vaccines which are reported on and discussed in social media forums," Dr Larson said.

"It recognises positive as well as negative sentiments and looks carefully at the content of both to understand what drives them."