New York, Oct 4 (IANS): People living in the US who believe that vaccines cause autism or other developmental disorders are increasingly using Twitter to spread anti-vaccine sentiment in the country, researchers have found.

For two decades anti-vaccine activists in the US have suggested that certain vaccines can lead to autism. There has been a surge in the tweets falsely linking life-saving vaccines to autism in recent years.

However, these Twitter posts are not a representative sample of overall public opinion, but rather a pulse of the level of anti-vaccine activism in an area, the researchers said.

In the study, affluent states such as California, Connecticut, Massachusetts, New York, and Pennsylvania as well as regions with a large number of new mothers were found to be most likely as the hubs of negative tweets.

"The debate online is far from over. There is still a very vocal group of people out there who are opposed to vaccines," said Chris Vargo, Assistant Professor at University of Colorado-Boulder, US.

"Half of the talk online that we observed about vaccines was negative," Vargo added.

For the study, published in the journal Social Science and Medicine, the team created a machine-learning algorithm to examine more than a half-million tweets from around the country between 2009 and 2015.

Between 2010 and 2015, the study found that anti-vaccine tweets became, overall, more common nationwide.

As the number of households that made over $200,000 annually increased or the number of women who had delivered a baby in the past 12 months increased, so did the amount of anti-vaccine tweets in a particular region.

Anti-vaccine tweet volume increased with news coverage of vaccine-related events.

"Monitoring anti-vaccination beliefs on Twitter can uncover vaccine-related concerns and misconceptions, serve as an indicator of shifts in public opinion and equip pediatricians to refute anti-vaccine arguments," Vargo noted.