The flu season began early in October of last year and has garnered attention for reports of morbidity among seemingly healthy people and pediatric patients.
Center for Disease Control data shows there have been detrimental seasons as closely as the 2014-2015 season, and while bad flu seasons are not entirely rare, this season peaked further above the epidemic threshold than usual. According to the CDC, 114 pediatric deaths have been reported due to the flu and a total of 23,324 confirmed hospitalizations since the beginning of the season.
Via the CDC
Mayo Clinic’s Dr. Steve Peters, who specializes in pulmonary medicine, said the elderly and people with underlying diseases that affect the immune system are still the ones most at risk for infection with the flu.
“If people have a common chronic disease like chronic lung disease, chronic heart disease, heart failure or other things like chronic rheumatologic conditions. If people have been on immune suppressing medicines like steroids,” said Peters of those who are at risk for infection.
While news coverage has centered on unlikely cases, according to the CDC, between 70 and 90 percent of flu deaths in a typical flu season are from those 65 years and older.
Mingtao Zeng, an assistant professor and researcher for the Center of Emphasis in Infectious Diseases at Texas Tech University, said the next highest population at risk is young children and infants less than six months. This is due to a weaker immune system, and a constraint in vaccine use and effectiveness.
How useful are vaccines?
According to the CDC, the vaccine this season was about 36 percent effective overall and 51 percent effective in children. About 80 percent of the pediatric deaths were children who were not vaccinated.
Even if the vaccine doesn’t stop you from getting infected, it can still make the infection less severe, so it’s still worth getting the flu shot.
“The current influenza vaccine is designed to protect against two types of influenza viruses: type A and B,” Zeng said. “It contains two type A influenza viral strains, H1N1 and H3N2, and two type B influenza viral strains.”
Ideally, Zeng said the antibodies in the body react to the dead virus in the vaccine and present with a two-armed response. This constitutes an immune system and cellular response that takes about four weeks to lead to immunity, but there are important factors as to whether a vaccine has an ideal response.
“First, you have to be perfectly matched. The virus it contains in the vaccine needs to be matched to the circulating virus,” said Zeng, whose area of research includes vaccine development.
The dominant virus responsible for this season’s epidemic is the Type A H3N2, he said, which means the vaccine matched the predictions of CDC researchers.
According to the CDC, the vaccine was about 10 percent less effective for the type A strain than type B.
Though the vaccine matched, Zeng said researchers don’t know exactly why the effectiveness was so low with this strain this season.
Wendy Walker, also an assistant professor and researcher from the Center of Emphasis in Infectious Diseases, said while the vaccine is not 100 percent effective, it is still a good proactive fight against infection.
“Even if the strain isn’t matched and you don’t make antibodies that prevent you from getting infected, when you’re vaccinated you get another response, it’s elicited by T cells and they kill the virus after it infects your cells,” Walker said. “Even if the vaccine doesn’t stop you from getting infected, it can still make the infection less severe, so it’s still worth getting the flu shot.”
Aside from the flu shot, Peters said there are other ways to avoid infection. He said the best choice is still avoiding those with the flu and staying home to rest when you contract it.
Pneumonia by far is the most feared complication of the flu, along with sepsis or shock.
He said staying home when you are sick is crucial to avoiding secondary infections. While the type A is a serious infection compared to type B, he said those secondary infections and a dangerous reaction to the virus or secondary bacteria are the problem, especially in a season like this.
What are flu-related complications?
According to a report from CNN in February, an otherwise healthy six-year-old and a 36-year-old mother of two both died from the flu soon after diagnosis. The culprit: sepsis.
“Sepsis occurs when you get an infection and then you get an overwhelming inflammatory response and usually the immunes system helps you to fight the infection but in sepsis the immune response is so strong that it actually hurts your body,” said Walker, whose research area is immunity and sepsis.
Dr. Steve Peters via Mayo Clinic
As reported by the CDC, one in three patients who die in the hospital have sepsis, and sepsis is caused by respiratory infections such as pneumonia in 35 percent of all cases. During a flu outbreak, pneumonia – an infection of the lungs leading to fluid accumulation – is a common secondary infection.
Peters said a secondary bacterial infection is common in the lungs, which may lead to an injury. With the activation of the cells and the susceptibility of the body, it doesn’t take long for bacteria to take over.
“It will usually be a strep or staph type of bacteria that would be inhaled and normally your body might fight that off but in the impaired state of a flu infection they are more likely to succeed in setting up as pneumonia,” he said. “Pneumonia by far is the most feared complication of the flu, along with sepsis or shock.”
He said it is common for people with the flu to feel they are getting better, and then their symptoms get worse days later. This can mean a secondary infection that can sometimes lead to sepsis, which is more life threatening than the flu virus itself.
The body, he said, then releases chemical mediators to fight off the invading flu virus or secondary bacteria and attacks itself. This shock state of the body leads to low blood pressure and organ failure, among other symptoms.
Pneumonia infection is so high in flu outbreaks, the CDC calculates the mortality rates together. Peters said avoiding those secondary infections that could lead to sepsis can be difficult but the key is to recognize symptoms early enough to treat effectively with antibiotics, especially in elderly patients at high risk.
Where do we go from here?
As this flu season comes to an end, researchers and medical practitioners focus on the next one ahead, and which issues to improve on.
A current angle of research looks at how the timing of vaccines can be used to best optimize the immune response. Walker is interested in studies out of England looking at circadian rhythms in the elderly, for her own research.
How can we make a better vaccine to be more effective in ages or for infants, or people who are immune deficient?
“They found that if they were vaccinated in the morning, they made higher levels of antibodies against the flu than if they vaccinated in the afternoon,” Walker said. “They weren’t actually able to correlate whether those people got the flu and whether it meant if they were vaccinated in the morning it meant they were less likely to contract the flu, but in terms of the antibody levels at least it seems like it was better if they were vaccinated in the morning.”
Peters and Zeng both see unpredictability as a hurdle in developing vaccines and preparing for a flu season.
“No one knows what makes the virulence of the strain vary so much from year to year,” Peters said. “This current Influenza A with H3N2 is the one that has been isolated the most often and Influenza A can be a severe infection. The frequency is probably once it takes off.”
When a strain has a high potential to spread across a population, he said an epidemic develops when many people become infected with the virulent strain.
Unfortunately, medical professionals do not know what makes one strain more prone to an epidemic than another until it has already spread.
Zeng and Walker said every season, the creator of the flu vaccine- the World Health Organization- has to make predictions as to what strains will be prevalent in the upcoming year. Problems that arise, Zeng said, are seasonal mutations in the virus, and predicting correctly. Along with optimal predictions, a possible way vaccines could be improved is a reformulation to better harness the immune response.
“This is the kind of thing people are working on,” Zeng said. “How can we make a better vaccine to be more effective in ages or for infants, or people who are immune deficient?”
About Anna Holland
