Sanofi has been officially criticised by the UK's Code of Practice Appeal Board after regulators found that the company often used a misleading interpretation of scientific data to make unfavourable comparisons with the UK's national respiratory syncytial virus (RSV) vaccination programme for infants. The ruling follows complaints by Pfizer over articles published in the Sunday Express, the Health Service Journal (HSJ) and related LinkedIn posts, which the regulator said risked weakening public confidence in vaccination at a time when trust remains fragile.

RSV is a common virus that usually causes cold-like symptoms but can lead to serious lung infections in babies, older adults and people with weakened immune systems. To protect newborns, the UK chose Pfizer's maternal RSV vaccine, given during pregnancy so protective antibodies pass naturally from mother to baby before birth. Other countries, including Ireland, adopted Sanofi's monoclonal antibody, Beyfortus (nirsevimab), a laboratory-made protein that provides babies with ready-made protection after birth.

The Appeal Board found that Sanofi compared early Irish data showing a sharp fall in infant RSV hospitalisations with UK figures collected only months after the maternal vaccination programme began. According to the regulator, that comparison ignored the time needed for vaccinated pregnancies to result in protected newborns, making it scientifically unsound to judge the programme's effectiveness so early.

The board said the claims were "premised on a very misleading interpretation of the data" and concluded that they unfairly disparaged both Pfizer's medicine and the UK's immunisation programme. It further stated that using misleading data "on multiple occasions" reflected "a complete absence of appropriate compliance checks and balances" and a corporate culture that "significantly brought the pharmaceutical industry into disrepute."

The regulator also criticised Sanofi's conduct during its exchanges with Pfizer and the Prescription Medicines Code of Practice Authority (PMCPA), saying effective self-regulation depends on "frankness, transparency and proper engagement at all stages of the process". The company was found to have broken several rules of the Association of the British Pharmaceutical Industry (ABPI) Code, such as making misleading claims, making comparisons without evidence, not keeping high standards, improperly promoting prescription medicines, and engaging in activities that could lower trust in the pharmaceutical industry.

The decision does not question the effectiveness of either RSV prevention strategy. Published studies, like the Phase III MATISSE trial in The New England Journal of Medicine and early reviews by the UK Health Security Agency and Public Health Scotland, have shown that vaccinating mothers against RSV can lower hospital visits for RSV in babies, and research has also shown that nirsevimab offers strong protection when used in immunisation programmes for infants. The regulator's concern centred on how the evidence was presented, not on the value of either intervention.

At the May 2026 hearing, Sanofi acknowledged the seriousness of the breaches and accepted that cultural, governance and compliance shortcomings existed at the time. The Appeal Board did not order an immediate PMCPA audit but told the company to come back in October 2026 with the results of an independent review and proof of any changes made before deciding if more penalties are needed.