Virologists Report Reversion Of FluMist Into Pathogenic Virus In Mice

Virologists, including the CDC’s own Virology, Surveillance, and Diagnosis Branch chief, reported in a paper published in the Journal of Virology that no study had ever been done specifically to determine if the attenuating temperature-sensitive phenotype in FluMist could ever revert and regain virulence to cause severe disease. FluMist was licensed over a decade ago and the FDA approved its use only for healthy, non-pregnant persons who are between the ages of 2-years-old through 49-years-old, according to Immunization Action Coalition. The paper was published in September, but the research only recently began showing up in social media.

A research team made up of experts in virology and infectious disease experts including Branch Chief David Wentworth, Dr. Bin Zhou of the J. Craig Venter Institute, Dr. Stacey L. Schultz-Cherry with the Department of Infectious Diseases at St. Jude Children’s Research Hospital and Deputy Director of the WHO’s Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds and other esteemed researchers published their paper entitled “Reversion of Cold-Adapted Live Attenuated Influenza Vaccine into a Pathogenic Virus.” The study examined the the nasal sprays branded FluMist.

FluMist was shown ineffective two flu seasons in a row.
FluMist, the intranasal flu vaccine, is believed to be very stable. Mutants that cause disease in humans have not been reported.
[Image by Sue Ogrocki/AP Images]

“A substantial amount of scientific and clinical evidence has proven that FluMist is safe and effective,” the researchers wrote. “Nevertheless, no study has been conducted specifically to determine if the attenuating temperature-sensitive phenotype can revert and, if so, the types of substitutions that will emerge (i.e., compensatory substitutions versus reversion of existing attenuating mutations).”

The research uncovered that “[s]erial passage of the monovalent FluMist 2009 H1N1 pandemic vaccine at increasing temperatures in vitro generated a variant that replicated efficiently at higher temperatures.” The researchers were clear that it did not mean that the vaccine is unsafe.

“The live attenuated influenza vaccine FluMist has been proven safe and effective and is widely used in the United States. The phenotype and genotype of the vaccine virus are believed to be very stable, and mutants that cause disease in animals or humans have never been reported. By propagating the virus under well-controlled laboratory conditions, we found that the FluMist vaccine backbone could regain virulence to cause severe disease in mice.”

They discovered several mutations that developed, and noted that the viruses that mutated also regained virulence and caused significant disease in the mice they were testing on. The severity was described as “comparable to that caused by a wild-type 2009 H1N1 pandemic virus.” Of course, this was in well-controlled laboratory conditions.

Nevertheless, the researchers did note that the study suggests that the “safety of LAIVs should be closely monitored after mass vaccination and that novel strategies to continue to improve LAIV vaccine safety should be investigated.”

Girl receives FluMist vaccine.
Pediatricians report children prefer the FluMist nasal vaccine over the jab.
[Image by Chris Gardner/AP Images]

Just before the 2016-2017 flu season arrived, the CDC’s Advisory Committee on Immunization Practices (ACIP) voted that the nasal spray vaccine for the seasonal flu should not be used this season only, as Inquisitr previously reported. The makers of the LAIVs had projected a supply of as many as 14 million doses that would be used in the United States this flu season, according to the CDC. The ACIP’s interim recommendation against using the nasal spray this season stemmed from research published in May of 2016 that indicated that the nasal flu vaccine offered little protection from the flu in the 2013-2014 and 2014-2015 flu seasons.

The CDC’s Dr. Brendan Flannery, the Center’s lead investigator for the U.S. Flu Vaccine Effectiveness Network, stated that the LAIVs had zero effectiveness against one strain of flu. The recommendation against using the FluMist this season is reportedly not expected to be a permanent recommendation for future seasons.

[Featured Image by Emma Werner/AP Images]