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2017-2018 Flu Season: A Retrospective

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You cannot escape hearing or reading about this year’s influenza outbreak. It seems every day there is more depressing news about the large number of individuals across the U.S. who have been hospitalized and the deaths of people of all ages, particularly children and young adults. While there is no doubt the current flu season is breaking records in the worst way, is it really as devastating as what is being reported? Just how pervasive and impactful has this year’s flu season been? How does it compare to prior years? In order to gain historical insight, we will cover the most recent seasonal flu pandemic, the 2009 H1N1 outbreak, and the worst of all time, the 1918 “Spanish” flu.

2017-2018 Influenza Season: The Facts

Even though flu activity still seems to be widespread, the data from the Centers for Disease Control and Prevention (CDC) indicates that the season has started to decline as the number of deaths and visits to the hospitals and clinics has dropped for the fifth week in a row. Recognizing the beginning of the flu season as October 1, 2017, CDC is reporting 81,508 fatalities from pneumonia and influenza through week seven of 2018, with 9,402 representing the flu portion of the figure. In addition, for the period of October 1, 2017, to March 3, 2018, the CDC also stated that 119 influenza-associated pediatric deaths have been reported, along with 24,644 laboratory-confirmed influenza-associated hospitalizations. Note, the flu season is far from over and could extend to May.

What explains the severity of the current flu season? Three factors have been cited by researchers. Healthy young men and women who died quickly of flu were most likely victims of a cytokine storm. When confronted with a new invader, the immune system sometimes overreacts, flooding the body with bio-chemicals called cytokines. A cytokine storm, which kills around 50% of those who develop it, is very similar to septic shock and can cause tissue and organ damage.

Gauging the effectiveness of the 2017 vaccine, the CDC’s Morbidity and Mortality Weekly Report (MMWR) tracked influenza cases from 1,700 adults and children in the U.S. and determined that the flu shot was 36% effective overall, yet was only 25% effective in preventing the H3N2 strain of influenza A. Poor results notwithstanding, getting vaccinated every year is still a very wise decision. Surprisingly, despite the efforts of health officials and doctors, the number of people obtaining the flu vaccine is decreasing slightly. Research is focused on the development of a universal flu vaccine that would address all strains and provide a lifetime of protection.

There are four types of influenza viruses — A, B, C and D — and seasonal flu is caused by influenza A and B. Different strains of these viruses circulate every year. The reason this year’s flu season is more severe than usual is because it includes H3N2, a strain of the influenza A virus that is difficult to prevent and causes more health complications. The CDC shows that for the data accumulated (tests performed by public health laboratories) from October 1, 2017, through February 17, 2018, influenza A represents 81.3% (28,895) of the number of positive specimens, with the H3N2 strain totaling 86.9% (25,104) of the A virus subgroup.

A significant reason why the H3N2 strain of influenza A is in such wide circulation is because it’s difficult to prevent with the flu vaccine. There are two main reasons behind this phenomenon. First, as this type of strain spreads from one person to the next, it mutates faster than other flu viruses, thus making it a challenge to produce an effective vaccine. Second, it is more difficult to grow H3N2 in fertilized embryos, where viruses for flu vaccines are produced. The typical mutation process of this virus within the egg weakens the effectiveness of the vaccine.

2009 H1N1 Swine Flu

Originating in Mexico, the swine flu spread north, with CDC estimating that the impact in the U.S. was around 61 million cases, 274,304 hospitalizations and 12,469 deaths. This strain is still in circulation; the World Health Organization (WHO) estimates H1N1 has killed 18,000 people worldwide since 2009. Initially in short supply that season, the vaccines for H1N1 are estimated to have an effectiveness rate of 56%. During the 2009-2010 season, the H1N1 strain struck children and under-65 adults more than adults over 65.

The delay in administering the vaccine to the public highlighted the worldwide shortcomings in vaccine production and distribution. Thereafter and to this day, improvements have been made to facilitate vaccines in an expedited manner at regional, national and international levels.

The medical community also learned from the 2009 season that two traits made people vulnerable to contracting severe influenza: pregnancy and obesity. Researchers from the California Pandemic Working Group estimated that persons with a body mass index (BMI) of 40 or greater were 3 times more likely to suffer a fatality from H1N1 compared to individuals with a normal BMI. The reason for this risk factor is that the higher the BMI, the greater likelihood of underlying pulmonary (lung) dysfunction. In the case of pregnant women, this group was found to have a 4 to 5 times greater likelihood of complications and hospitalization when contracting H1N1.

Changes in the immune system, heart, and lungs during pregnancy make pregnant women (and women up to two weeks postpartum) more prone to severe illness from flu, including illness resulting in hospitalization

1918 Influenza Pandemic: A Black Swan Event

The “Spanish” flu pandemic during 1918-1919 killed 50 million (older estimate) to 100 million (more current estimate) people worldwide (3-5% of the world’s population). It afflicted over 25-28% of the U.S. population, with 500,000 to 675,000 deaths. In one year, the average life expectancy in the United States dropped by 12 years. It is recognized as the most devastating pandemic in recorded world history. It was the first of the two pandemics involving H1N1 virus (the other in 2009).

There are numerous theories to explain the high mortality rate of the 1918 influenza pandemic. Some research implies that this specific variant of the virus had an unusually aggressive nature.

More current investigations postulate that the viral infection itself was not more aggressive than any previous influenza; instead, the special circumstances originating from World War I of overcrowded medical camps and hospitals, poor hygiene and malnourishment spawned a bacterial superinfection. Individuals with mild cases of influenza stayed home, but those with severe cases were often crowded together in camps and hospitals, increasing transmission of the virus.

Yet another theory attributes the 1918 catastrophe to cytokine storm. In 2005, scientists disclosed that they had successfully ascertained the gene sequence of the 1918 virus. Studies concluded that the monkeys infected with the virus died when their immune systems overreacted to the virus. Scientists now believe that cytokine storm was significantly instrumental in the high death rates among healthy young adults. The consensus among experts that have studied the 1918 Spanish flu is that this type of pandemic could occur again, but the impact could be lower. We now have vastly improved medical facilities, vaccinations can be developed in a shorter period and distributed widely, and with current technology we can share current research with the click of a button.

Influenza, whether seasonal or unique strains, will not be eradicated in our lifetime, or possibly ever. The good news is that as long as countries, health organizations and medical facilities are prepared for the next possible pandemic, combine their resources, and share knowledge, the impact on the population could be reduced.



RGA Group Insurance Insight is published by the Group Reinsurance Teams of RGA Reinsurance. This publication’s mission is to provide news and information to group insurance professionals and to support the group insurance market. The information contained in the articles represents the opinion of the authors and does not necessarily imply or represent the position of the editors or RGA Reinsurance Company. Articles are not intended to provide legal, consulting or any other form of advice. Any legal or other questions you have regarding your business should be referred to your attorney or other appropriate advisor.

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The Author

  • Rick Becchetti
    Senior Risk Management Analyst
    U.S. Group Reinsurance

Summary

While there is no doubt the current flu season is breaking records in the worst way, is it really as devastating as what is being reported? An investigation of the group insurance implications of the global spread of this infectious disease. 
  • avian flu
  • epidemics
  • genetic
  • genome
  • infectious disease
  • influenza
  • insurance medicine
  • MERS
  • morbidity
  • mortality assumptions
  • mortality experience
  • mortality trends
  • pandemic