ID Consult

Don’t give up on influenza vaccine


 

Influenza vaccine needs some help with its image.

I suspect most health care providers have heard the complaint, “The vaccine doesn’t work. One year I got the vaccine, and I still came down with the flu.”

Over the years, I’ve polished my responses to vaccine naysayers.

Influenza vaccine doesn’t protect you against every virus that can cause cold and flu symptoms. It only prevents influenza. It’s possible you had a different virus, such as adenovirus, coronavirus, parainfluenza virus, or respiratory syncytial virus.

Dr. Kristina K. Bryant, a pediatrician specializing in infectious diseases at the University of Louisville (Ky.) and Norton Children's Hospital in Louisville
Dr. Kristina A. Bryant
When you are vaccinated late in the season, the vaccine might not have a chance to work. It is possible you were exposed to influenza right around the time you were vaccinated and before you had a chance to make the antibodies that would have protected you against flu.

Some years, the vaccine works better than others because there is a mismatch between the viruses chosen for the vaccine, and the viruses that end up circulating. Even when it doesn’t prevent flu, the vaccine can potentially reduce the severity of illness.

The discussion became a little more complicated in 2016 when the Centers for Disease Control and Prevention Advisory Committee on Immunization Practices withdrew its support for the live attenuated influenza virus vaccine (LAIV4) because of concerns about effectiveness. During the 2015-2016 influenza season, LAIV4 demonstrated no statistically significant effectiveness in children 2-17 years of age against H1N1pdm09, the predominant influenza strain. Fortunately, inactivated injectable vaccine did offer protection. An estimated 41.8 million children aged 6 months to 17 years ultimately received this vaccine during the 2016-2017 influenza season.

Now with the 2017-2018 influenza season in full swing, some media reports are proclaiming the influenza vaccine is only 10% effective this year. This claim is based on an interim analysis of data from the most recent flu season in Australia and the effectiveness of the vaccine against the circulating H3N2 virus strain. News from the U.S. CDC is more encouraging. The H3N2 virus contained in this year’s vaccine is the same as that used last year, and so far, circulating H3N2 viruses in the United States are similar to the vaccine virus. Public health officials suggest that we can hope that the vaccine works as well as it did last year, when overall vaccine effectiveness against all circulating flu viruses was 39%, and effectiveness against the H3N2 virus specifically was 32%.

Toddler is held by mother while being vaccinated by doctor. KatarzynaBialasiewicz/Thinkstock
Of course, we’ll know more over the next couple of months. The effectiveness equation is a complicated one, and intense public interest is changing the dialogue about flu vaccine.

I’m upping my game when talking to parents about flu vaccine. I mention one study conducted between 2010 and 2012 in which influenza immunization reduced a child’s risk of being admitted to an intensive care unit with flu by 74% (J Infect Dis. 2014 Sep 1;210[5]:674-83). I emphasize that flu vaccine reduces the chance that a child will die from flu. According to a study published in 2017, influenza vaccine reduced the risk of death from flu by 65% in healthy children and 51% in children with high-risk medical conditions (Pediatrics. 2017 May. doi: 10.1542/peds.2016-4244).

When I’m talking to trainees, I no longer just focus on the match between circulating strains of flu and vaccine strains. I mention that viruses used to produce most seasonal flu vaccines are grown in eggs, a process that can result in minor antigenic changes in the hemagglutinin protein, especially in H3N2 viruses. These “egg-adapted changes” may result in a vaccine that stimulates a less effective immune response, even with a good match between circulating strains and vaccine strains. For example, Zost et al. found that the H3N2 virus that emerged during the 2014-2015 season possessed a new hemagglutinin-associated glycosylation site (Proc Natl Acad Sci U S A. 2017 Nov 21;114[47]:12578-83). Although this virus was represented in the 2016-2017 influenza vaccine, the egg-adapted version lost the glycosylation site, resulting in decreased vaccine immunogenicity and less protection against H3N2 viruses circulating in the community.

The real take-home message here is that we need better flu vaccines. In the short term, cell-based flu vaccines that use virus grown in animal cells are a potential alternative to egg-based vaccines. In the long term, we need a universal flu vaccine. The National Institute of Allergy and Infectious Diseases is prioritizing work on a vaccine that could provide long-lasting protection against multiple subtypes of the virus. According to a report on the National Institutes of Health website, such a vaccine could “eliminate the need to update and administer the seasonal flu vaccine each year and could provide protection against newly emerging flu strains,” including those with the potential to cause a pandemic. The NIH researchers acknowledge, however, that achieving this goal will require “a broad range of expertise and substantial resources.”

Until new vaccines are available, we need to do a better job of using available, albeit imperfect, flu vaccines. During the 2016-2017 season, only 59% of children 6 months to 17 years were immunized, and there were 110 influenza-associated deaths in children, according to the CDC. It’s likely that some of these were preventable.

The total magnitude of suffering associated with flu is more difficult to quantify, but anecdotes can be illuminating. A friend recently diagnosed with influenza shared her experience via Facebook. “Rough night. I’m seconds away from a meltdown. My body aches so bad that I can’t get comfortable on the couch or my bed. Can’t breathe, and I cough until I vomit. My head is about to burst along with my ears. Just took a hot bath hoping that would help. I don’t know what else to do. The flu really sucks.”

Indeed. Even a 1 in 10 chance of preventing the flu is better than no chance at all.

Dr. Bryant is a pediatrician specializing in infectious diseases at the University of Louisville (Ky.) and Norton Children’s Hospital in Louisville. She said she had no relevant financial disclosures. Email her at pdnews@frontlinemedcom.com.

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