BANGKOK, THAILAND – Thai health authorities rejected viral online claims that mRNA vaccines carry a hidden cancer risk from SV40 contamination.
Authorities debunk viral vaccine cancer claims
The Anti-Fake News Center Thailand (AFNCT) examined circulating social media posts that alleged dangerous cancer risks from mRNA vaccines. Working with the Department of Medical Sciences (DMSC), the agency verified the scientific basis of the allegations.
The review concluded that the online claims were completely fabricated.
“There is no evidence whatsoever of SV40 contamination in modern mRNA vaccines.”
said the agency.
SV40 fears traced back to older polio vaccines
The false posts had asserted that current vaccines contained cancer-causing viral remnants. Officials described this as a dangerous misconception that had now been refuted on scientific grounds.
SV40 (Simian Virus 40) was identified in 1960 in monkey kidney cells, which were then used to produce polio vaccines. Later laboratory experiments showed that SV40 could cause tumours in some test animals, raising questions about potential effects in humans.
No clear link between SV40 and cancer in humans
Long-term observations of people who received polio vaccines during that period produced no clear proof of a higher cancer risk from SV40. Researchers did not establish a definitive causal connection between SV40 exposure via those vaccines and human cancers.
These historical findings are now being misused in online narratives that ignore the major changes in vaccine technology since the 1960s.
Modern mRNA production rules out SV40
Officials stressed that modern mRNA vaccines are manufactured in a completely different way from the polio vaccines of that era.
“Today’s mRNA vaccines are synthesized in vitro and do not use monkey cells as a production source at all,”
said the DMSC.
They stated that this manufacturing method made the possibility of SV40 contamination fundamentally and completely impossible. According to the authorities, the underlying technology had advanced significantly.
Strict quality controls and international standards
Each vaccine batch underwent a multi-stage purification process using advanced technology, officials said. These strict quality controls ensured that all residual substances were kept at an extremely low level.
The Thai standards were in line with international guidelines, meaning patients in Thailand were considered as safely protected as those in Europe or the United States.
Organised networks and evolving misinformation
Experts saw a worrying pattern behind the recurring waves of vaccine rumours, noting that fears among the population were being deliberately fuelled.
“Misinformation about vaccines is not new, but it is becoming more and more sophisticated,”
said a health economist.
Well-organised networks often stood behind such campaigns, using fear and uncertainty as a business model. The authorities described their latest intervention as a clear response to those tactics.
Call for critical thinking and trusted sources
The DMSC urged citizens to question health-related information critically and to rely on official sources such as the Ministry of Public Health for reliable facts.
“Do not let yourself be unsettled by scaremongering on the internet. Trust in science and in the strict controls of our authorities,”
said a spokesperson.
People with questions about vaccination were advised to consult their own doctor rather than anonymous posters online. Officials said the scientific evidence had been presented and that the relevant facts were now on the table.