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No Evidence Flu Vaccine Increases Strep A Infections, Contrary to Online Claims

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SciCheck Digest

Several European countries have reported an early spike of group A strep infections, mostly among children, including cases of rare but deadly bacterial infections. There is no evidence the increase is being caused by nasal spray flu vaccines, as social media posts baselessly suggest. Flu vaccination may even indirectly prevent strep A.

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Multiple countries in Europe are observing an increase in infections caused by group A streptococcus, or Streptococcus pyogenes, bacteria. Strep A can cause several diseases such as scarlet fever, strep throat or impetigo, all of which are usually mild but very contagious. The bacteria is commonly found in the throat or on the skin, but in rare occasions it can get into certain parts of the body or bloodstream, causing a serious disease called invasive group A strep, or iGAS. 

On Dec. 15, the World Health Organization issued an outbreak alert, reporting an increase of iGAS disease and scarlet fever cases in France, Ireland, the Netherlands, Sweden and the United Kingdom, mostly affecting children under the age of 10. Several deaths associated with iGAS have been reported in children in the U.K., France and Ireland since September, according to a shared statement by the WHO and the European Centre for Disease Prevention and Control

In the U.K., for example, there were 27,486 notifications of scarlet fever from Sept. 12 to Dec. 18, compared with a total of 3,287 for the same period in the last comparably high season (2017-2018). Health authorities have said cases of iGAS remain rare, but are also higher than usual. As of Dec. 22, England has reported 94 deaths in all age groups, including 21 in children under 18.

In the U.S., the Centers for Disease Control and Prevention is examining a potential increase in iGAS among children as well. A CDC representative told us the agency “is hearing anecdotes from some U.S. doctors of a possible increase in iGAS infections among children in the United States and is investigating this increase.” According to an NBC News story published on Dec. 15, children’s hospitals in Arizona, Colorado, Texas and Washington are seeing more iGAS cases than usual. Health officials in Minnesota reported 46 iGAS cases in November.

Scientists are not certain what is causing the outbreak. 

U.K. authorities have said that there is no evidence of a new strain of the bacteria, and that the increase in disease “is most likely related to high amounts of circulating bacteria and social mixing.” The surge follows a period of reduced exposures during the COVID-19 pandemic, which may have decreased population immunity to the bacteria. But some say it’s too soon to know if that’s causing the spike.

“There are a lot of things that seem to be a bit strange happening after the lockdowns,” Claire Turner, a research fellow at the School of Biosciences at University of Sheffield in the U.K., told Nature. “But it’s hard to say whether that’s causing the surge right now, especially given that we have had surges prior to the pandemic.”

The WHO and the CDC have said the surge is likely associated with the increase in other respiratory viral infections, such as influenza and respiratory syncytial virus, or RSV.

“People with concurrent or preceding viral infections, such as influenza and varicella (chickenpox), are at increased risk for iGAS infection,” the CDC noted in a Dec. 22 health advisory.

But people who oppose vaccines are pushing a different theory, baselessly suggesting a link between the spike in deadly strep infections and nasal spray flu vaccines.

“Four weeks ago, all UK PRIMARY aged children get live flu nasal spray. Today, primary aged children dying from strep. Dot to dot,” reads a meme widely shared on social media.  

“Hmmm no coincidence….. they roll out these vaccines and death follows not too far behind,” reads an Instagram post that shows the meme next to a screenshot of a news article reporting the death of a sixth child from strep A in the U.K. 

The CDC recommends that everyone 6 months and older get a flu vaccine every season, with some exceptions. The nasal spray flu vaccine, which is one of several options, is especially convenient for those who want to avoid a needle. Its use is approved for healthy people who aren’t pregnant, ages 2 to 49.

According to CDC estimates, during the 2019-2020 season, the flu vaccine prevented 105,000 hospitalizations and 6,300 deaths associated with influenza.

No Link Between Nasal Spray Flu Vaccine and Strep A Infections

There is no evidence that the nasal spray flu vaccine causes or increases susceptibility to strep A. The nasal spray flu vaccine contains weakened influenza viruses that are not able to reproduce in the lungs, and it doesn’t cause the flu. Strep A diseases are caused by bacteria, not viruses.

“CDC is also not aware of a relationship between Live Attenuated Influenza Vaccine (LAIV, or the nasal spray flu vaccine) and Group A Streptococcal infections,” a CDC spokesperson told us in an email.

Dr. Paul A. Offit, an infectious diseases physician at Children’s Hospital of Philadelphia and a vaccine expert, told us respiratory viruses can cause a disruption of the mucosal surface integrity, facilitating the entrance of bacteria. But there is no evidence that the weakened viruses in the nasal spray flu vaccine are capable of that, he said. 

“The vaccine has been out for almost 10 years, so there is a large record of safety,” Offit told us in a phone interview. “If this really was a true causal association, I think you would have seen it.” 

More importantly, Offit added, live viruses that have not been weakened, like circulating flu viruses, are much more likely to facilitate the entrance of bacteria because they “reproduce much, much better at the mucosal surface than an attenuated virus would.” Therefore, Offit said, it is more likely that by preventing the flu, the vaccine could indirectly prevent strep A.

That is what researchers from the U.K. Health Security Agency found in a recently posted study. The study, which hasn’t yet been published or peer-reviewed, evaluated the epidemiological impact of the pediatric nasal spray flu vaccine program in England on the frequency of group A infections, including scarlet fever and iGAS. It found that the nasal spray flu vaccine, or LAIV (live attenuated influenza vaccine), was associated with a decrease in some strep A infections in certain age groups.

“Our findings are compatible with the paediatric LAIV programme reducing the incidence of GAS and iGAS infections among children and support attaining high uptake of childhood influenza vaccination,” the authors wrote.

“Nasal flu vaccine DOES NOT increase risk of strep A in kids,” Dr. Meaghan Kall, an epidemiologist with the U.K. Health Security Agency, said on a Twitter thread, linking to the study. “Flu vaccine can prevent flu, and indirectly prevent strep A infection. #GetVaccinated,” she added.

Misrepresented Study in Mice 

Some social media posts linking the nasal spray flu vaccine to strep A infections show screenshots of a 2014 study titled “Live attenuated influenza vaccine enhances colonization of Streptococcus pneumoniae and Staphylococcus aureus in mice,” as proof of the association. 

“SCIENCE DOCUMENT: INFLUENZA (FLU) VACCINE ENHANCES STREPTOCOCCUS (STREP) IN MICE (AND IN CHILDREN),” reads an Instragram meme showing a screenshot of the study. “YOUR GOVERNMENT HAS GIVEN YOUR CHILDREN STREP FOR CHRISTMAS,” a user on social media who shared the meme added. 

But Dr. Jon McCullers, chair of pediatrics at the University of Tennessee Health Science Center and one of the authors of the study, told us the paper is being misinterpreted.

“We were studying Streptococcus pneumoniae, not Group A Strep. These are very different bacteria. Group A Strep has not been studied with FluMist to my knowledge, and the bacteria behave differently when paired with respiratory viruses,” he told us in an email, referring to the brand name of the nasal spray flu vaccine.

The research — which was conducted in mice, not in humans — found that the vaccine increased the amount of the bacteria the authors were studying in the upper part of the throat behind the nose of mice, McCullers said. But the study also found that this increase didn’t cause serious disease.

“Importantly, we did demonstrate that serious, invasive disease did not occur following live, attenuated influenza virus infection as it does with regular influenza viruses,” McCullers said (emphasis is his). 

Whether these findings would apply to group A streptococcus in mice, or in humans, is unknown. McCullers said it was plausible that the nasal spray flu vaccine “could enhance the amount of bacteria in the nasopharynx, and might enhance transmission of strep throat,” but it was unlikely to cause children to get scarlet fever or other skin diseases. In any case, he added, there is no data to support the notion of the vaccine increasing the spread of strep A — and since respiratory viruses are ubiquitous, the vaccine’s impact would be negligible. 

Again, as we said, by preventing flu, the vaccine might actually prevent strep A — something that is not reflected in the mouse experiment.

Unfounded Side Effect Claim

Other social media posts misleadingly point to a database of potential vaccine side effects to link the flu nasal spray vaccine to strep A. But that misunderstands the database. 

“Strep A is the flu nasal spray,” claims a post on Instagram, using a screenshot of VigiAccess, an online tool for searching potential adverse reactions within a WHO global database, where streptococcal infection is listed as a reported potential side effect. (Under “Infections and infestations,” there are 40 and 37 reports for “streptococcal infection” and “pharyngitis streptococcal,” respectively, out of a total of almost 298,000 reports.)

But these listings in the database don’t mean the strep A infection is a side effect of the vaccine. As VigiAccess’ website explains, reports in the database are not vetted and no “causal relation has been confirmed.” That means, as VigiAccess notes, that “potential side effects should not be interpreted as meaning that the medicinal product or its active substance either caused the observed effect or is unsafe to use.”

Just as with the Vaccine Adverse Event Reporting System in the U.S., data from VigiAccess has been misrepresented before. The databases include reports of post-vaccination events regardless of whether they might be due to the vaccine or not.

Editor’s note: SciCheck’s articles providing accurate health information and correcting health misinformation are made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation.


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