With flu season rapidly approaching, many doctors and public health experts are concerned the lack of an influenza nasal spray option this fall will lead to lower rates of vaccination among children and a worse flu season.
In late June, the Centers for Disease Control and Prevention’s Advisory Committee for Immunization Practices recommended against the use of the FluMist nasal spray, after the inhaled vaccine showed almost no effectiveness in preventing the flu over the past three seasons. Although the FluMist vaccine can still be sold in the U.S., it is unlikely that many pediatric clinics will offer the nasal spray, leaving the traditional flu shot as the only option.
“I think it’s going to be a bad flu year because a lot fewer people are going to be vaccinated,” said Dr. Logan Clausen, medical director at Central Oregon Pediatric Associates, “which should only motivate you more to get the vaccine.”
FluMist has been on the market since 2003, and at least initially, data showed the nasal spray was more effective than the traditional flu shot, particularly among children. Although FluMist accounted for only 8 percent of the total flu vaccine market, it made up about a third of the pediatric market.
“The flu is a surprisingly serious illness for a lot of kids, especially for the younger kids,” said Dr. Brooks Booker, a pediatrician with Bend Memorial Clinic. “Kids under 6 months of age cannot get vaccinated for the flu, so it’s important that everybody around them gets the vaccine.”
Kids are more likely to have complications from the flu and more likely to be hospitalized.
“There are definitely many kids that die each year from the flu,” Clausen said. “The rate of complications and severity is much higher in children than it is for the rest of the population.”
It’s still unclear what went wrong with the FluMist, but for the 2015-16 flu season the spray showed only 3 percent effectiveness against circulating flu strains among children age 2 to 17, compared with 63 percent effectiveness for the flu shot. Immunization experts have proposed a number of theories for why FluMist seems to have lost its effectiveness.
The FluMist uses a weakened live virus to stimulate an immune response, building up antibodies that can then fight off future infections. But the inhaled spray provides a thousand times less of the virus than the flu shot and relies on the virus to replicate once inhaled.
“If it doesn’t replicate adequately, then you’re not going to get an immune response,” said Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia.
Speculation has swirled over the change in FluMist three years ago from containing two influenza A and one influenza B strains, to two A and two B strains.
“You could argue that when they added that additional B strain, there was a dominant strain, one strain reproduced itself more than the other strains, thus not allowing the other strains to replicate as well,” Offit said.
That’s happened with other vaccines, including the oral polio vaccine and the rotavirus vaccine that Offit developed. Those vaccines are generally given more than once, giving the immune system a second chance to react to strains that didn’t replicate enough the first time. But that’s not practical with the flu vaccine that must be given every year.
“FluMist is given as a single dose,” Offit said, “so you’re jumping without a net.”
Offit puts more stock in a different theory. FluMist’s problem has been in mounting an effective response against the H1N1 strain of flu. That’s the strain that caused the so-called swine flu pandemic in 2009. Even before FluMist went from three to four strains, the spray showed limited effectiveness against H1N1.
Offit believes it may be a problem with the particular version of H1N1 used to make the vaccine.
H1N1 was the dominant strain in two out of the last three years, so that could explain FluMist’s recent struggles.
There are potentially other explanations as well.
Last year, the spray’s manufacturer, AstraZeneca, reported that the H1N1 portion of the vaccine might be overly sensitive to heat. The company had data from the 2013-14 flu season showing that doses that were unloaded from distribution trucks on warmer days were less effective. The company altered the formulation to try to address the problem, but the vaccine still showed little effectiveness against H1N1 in the 2015-16 flu season.
It’s also possible that because H1N1 has been circulating for a number of years, more individuals have been exposed to it and may already have some antibodies to that strain in the vaccine.
“It may be that they have enough antibodies on board to block the replication of the virus, so that it doesn’t really meaningfully boost their immune response,” said Dr. Paul Cieslak, medical director of the immunization program for the Oregon Health Authority.
It’s unclear whether AstraZeneca will be able to discover the true cause of the FluMist’s woes and rehabilitate the vaccine in the eyes of the advisory committee. That will leave pediatric clinics trying to convert as many patients as possible from the nasal spray to the shot this year. Flu vaccinations typically start in late September and continue through the winter months.
If the lack of FluMist this year leads to fewer kids being vaccinated, the upcoming flu season could be much worse than it would otherwise be.
Children tend to contribute more to the spread of flu than do adults. Studies have shown that when kids get the flu, they are sick longer and they shed more virus. Because they spend so much time in close quarters with other children in school during the flu season, kids can spread flu through the community much faster.
“If we vaccinate significantly fewer numbers of kids, I think we’re going to have a lot more flu,” Cieslak said. “They have the potential of transmitting it to more people and I really do believe that if we got high numbers of kids vaccinated, it may indirectly protect a lot of adults as well.”
By: Markian Hawryluk (The Bulletin).
Photo: Carlos Barria (Reuters).
Review: Emerging Market Formulations & Research Unit, FLAGSHIP RECORDS.
For The #FacebookTeam