False claim persists that flu vaccine caused strep A in mice

A post on Facebook says: “Well well well.... The live flu 'prick' has been found to cause Strep A.... and what's happening to children right now? They are giving them the live flu nasal spray. I am just following the 'pier reviewed' science! [sic]”

The post also includes screenshots of a Daily Mail article from early December about strep A in children, which does not mention the flu vaccine, and a 2014 paper entitled “Live attenuated influenza vaccine enhances colonization of Streptococcus pneumoniae and Staphylococcus aureus in mice”.

As we have written multiple times before, this study did not show that the flu vaccine caused strep A in mice. It actually found that the live attenuated flu vaccine (the type given to school children) increases the likelihood of finding two other types of bacteria in the upper respiratory tract of mice. 

Neither of these bacteria strains are the type that causes strep A infections. Strep A, also known as GAS or group A streptococcus, is a bacteria sometimes found in the throat or on the skin, often carried harmlessly. It usually causes mild illnesses such as a sore throat, and in other cases it can cause scarlet fever, which is usually mild. 

More serious and even life-threatening infections can occur when the bacteria enters deeper parts of the body, such as in the lungs or the bloodstream—these are termed invasive group A strep (iGAS) infections. 

As of 15 January, 30 children in England have sadly died with iGAS since September 2022.

Despite sounding similar, streptococcus pneumoniae (one of the bacteria types in the paper) and strep A (group A streptococcus) are different types of bacteria. The term streptococcal refers to a group or genus of bacteria defined by their microscopic appearance. Within this genus are many different species—including strep A, group B strep (which is linked to infections in childbirth) and strep pneumoniae.

The study looked for two strains of streptococcus pneumoniae, and did not find any evidence of an increased risk of severe infection or death caused by the strains in vaccinated mice.

The study also highlights that while flu vaccination with live attenuated vaccines “primes the upper respiratory tract for increased bacterial growth and persistence of bacterial carriage” in a very similar way to an actual flu virus infection (sometimes referred to as wild-type influenza), it doesn’t increase severe bacterial disease in the lower respiratory tract in the way an actual flu virus infection can.

Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading told Full Fact last month: “When you get flu, often what kills you [...] is a bacterial infection further down in your lungs. So you don't get that with the vaccine, but you do with wild type flu.” 

And there’s some evidence that the flu vaccine may even reduce strep A infections in children. 

We’ve previously written about a pre-print from the UK Health Security Agency which found a reduction in strep A infections in areas where more children received the nasal flu vaccine, though it said “there was no difference in scarlet fever or invasive group A strep (iGAS) notifications.”

The Medicines and Healthcare products Regulatory Agency (MHRA) previously told Full Fact: “Millions of children and adolescents have received this vaccine as part of the national flu immunisation programme and an increased risk of Strep A infections has not been identified as a safety concern.

“The MHRA closely monitors the safety of all vaccines used in the UK, including [the nasal flu vaccine] and the MHRA’s position remains that the benefits associated with this vaccine continue to outweigh any risks.”

Image courtesy of Kelly Sikkema