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Johns Hopkins Bloomberg School of Public Health


Keyword: influenza

This post originally appeared on The Conversation and is cross-posted here with permission.

By Bill Moss


In the US the risk of getting measles or dying from influenza is greater than the risk of getting Ebola. Jaime R Carrero/Reuters

News that a doctor in New York City tested positive for Ebola sparked mandatory quarantine orders for heath workers returning from West Africa in New York and New Jersey last week. The outbreak has killed nearly 5,000 people in West Africa, but only a handful of cases have been reported in the United States. Still, the virus has sparked widespread fear in the US. Views that Ebola is an exotic disease spreading out of control within Africa, with horrific symptoms, inevitable death, and limited means to prevent transmission are contributing to this fear. However, these fears are fueled by a misunderstanding of risk.

The outbreak is a tragic, public health emergency in urgent need of a massive and coordinated global health response. Fear of contagion is justified in communities where incidence is increasing and where protective measures are limited and health care is stretched beyond capacity.

However, this is not the case in the United States. The perceived risk to Americans is exaggerated. The risk of contracting Ebola in the US or the virus reaching epidemic proportions is very, very low.

The fact is, in the United States the risk of infection with measles virus or death from influenza virus is far greater.

Measles is more infectious than Ebola

Although the outbreak in West Africa is increasing exponentially, Ebola is not as contagious as many other infectious diseases. Transmission requires direct contact with infected body fluids. Measles, influenza and pertussis (whooping cough) on the other hand, are spread by respiratory secretions. They are much more explosive because transmission does not require direct contact with an infected person.

The speed with which an outbreak grows depends on how many additional people are infected by each infectious case and the time interval between infections. To put the current Ebola numbers in context, one person with Ebola will on average infect only 1.5 to 2.2 additional people. The relatively low number of people infected by a single case should make it easier to interrupt transmission. Further facilitating control is the fact that a person with Ebola is most infectious after the onset of signs and symptoms.

By contrast, a person with measles is infectious for several daysbefore they become sick. And a person with measles will on average infect 12 to 18 additional people. This year 594 measles cases have been reported in the United States through September 29th, the most in two decades. These cases represent 18 measles outbreaks in 22 states.

An estimated 122,000 people - mostly children - worldwide died of measles in 2012, about 330 measles deaths every day. In the US the increasing number of measles cases is mostly due to people visiting countries with measles outbreaks and carrying the virus back home and into communities in which large numbers of people are not vaccinated.

Measles is also becoming a public health problem in countries affected by Ebola. Immunization services have ceased in many affected areas as health care workers are redeployed to fight Ebola and the public loses confidence in the health care system. Cases of measles have been reported in Liberia and may spread to neighboring countries and beyond.


Instead of worrying about Ebola, make sure your vaccinations are up to date. Brian Snyder/Reuters

Vaccines and risk perception

As panic over Ebola grows, it’s worth asking why Americans are becoming more complacent to the threat of vaccine-preventable diseases.

Some Americans distrust vaccines and misunderstand the risks and benefits. Most Americans with measles this year were unvaccinated and declined vaccination because of religious, philosophical or personal objections. The largest measles outbreak this year spread within communities in Ohio with low vaccination coverage, with smaller outbreaks in California and New York City.

As with Ebola, early diagnosis, isolation and notification are critical to preventing further spread. Unlike Ebola, we have a highly effective and safe vaccine that can prevent measles. The unvaccinated individuals who developed measles in the United States misjudged the risk to themselves and their communities.

Measles isn’t the only risk. As many as 50,000 people die in the US of influenza virus infection in a single season. Influenza vaccine coverage in the United States during the 2013-2014 season was only 59% among children and 42% among adults, putting those most likely to develop severe disease - young infants and the elderly - at risk.

Again, unvaccinated individuals misjudge the risk and consequences of influenza. The Centers for Disease Control and Prevention tracks deaths due to influenza in children. During the 2012-2013 influenza season, 171 children died of influenza in the United States and 109 children died during 2013-2014 season. Although the influenza season has just started, one child death has already been reported in other words the same number of deaths currently due to Ebola in the United States.

Some may fear of exposing themselves or their children to risk from vaccines, even though these fears have been disproved time and again. They may do so without calculating the real risk of actually contracting the infection that these vaccines prevent. The risk might be masked thanks to herd immunity, but outbreaks of measles and whooping cough show the risk is growing. From January 1 to August 16, 17,325 cases of whooping cough were reported in the United States, a 30% increase over the same period in 2013. In California alone, which is experiencing a particularly large outbreak, 312 people have been hospitalized, most of whom were young infants.

Ebola vaccines are currently in development and testing. Most experts agree an Ebola vaccine would be a welcome tool, even if supplies limit use to health care workers. But this begs another question – how many Americans would be willing to receive an Ebola vaccine?


Bill Moss is Professor, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health; Director of Epidemiology, International Vaccine Access Center at Johns Hopkins University


William Moss receives funding from the National Institutes of Health and the Bill & Melinda Gates Foundation. He is affiliated with the World Health Organization as a member of the Strategic Advisory Group of Experts Working Group on Measles and Rubella.

By Jillian Murray

 “Influenza… what about HIV? That’s what people are dying from here.”

These are the words I heard in countless conversations while working on an influenza research project in South Africa last summer. Nearly every time I mentioned I was working on a public health research project I was met with a chorus of “ohhh HIV.” After explaining that I was, in fact, researching influenza, the conversation usually shifted to wondering why I would focus on something other than HIV.

I remember leaving some people unconvinced of the importance of studying respiratory diseases. Many had an emotional connection to HIV and recounted stories of people they knew dying of AIDS, but were unable to recall someone who died of influenza. In some populations, this acute awareness of the devastation of the HIV/AIDS epidemic has led to an ideology where an HIV diagnosis is mutually exclusive of other diseases.

Jillian Murray and a colleague.

Jillian Murray and a colleague in the Soweto township in Johannesburg during interviews for a health survey.

I found it interesting to witness the distinct hierarchy in the perceived importance of certain diseases. Influenza causes annual worldwide epidemics and can be a life-threatening complication of many other diseases, but because many people rank it’s severity slightly above the common cold, it is often assumed to be rather harmless. This is not only true in settings where there are other high priority communicable diseases, but is a common perception in North America as well.

The true burden of influenza is not well described in many developing countries. However, the burden is expected to be higher in developing compared to developed countries because of underlying factors that contribute to greater severity of disease – factors like crowding, low birth-weight, malnutrition and HIV, among others. In contrast to developed countries where the burden is primarily in the elderly population, these socio-economic factors play a role in broadening the demographic that is most at-risk for severe influenza in South Africa.

A better understanding of the burden of influenza is important for pandemic planning and more effective distribution of vaccine supply. While in South Africa, I worked under the supervision of Daniel Feikin, IVAC’s Director of Epidemiology. With the help of researchers at the National Institute of Communicable Diseases, we used a statistical model that adjusted for influenza risk factors between different provinces to estimate the burden of severe influenza at the provincial and national levels.

As it turned out, my work was very much related to HIV, which severely compromises the immune systems of those affected. There is evidence that HIV-positive individuals suffer a much greater mortality rate from influenza than HIV-negative individuals and that the risk for acquiring influenza in HIV-positive individuals is much greater than in HIV-negative individuals. A high prevalence of HIV, such as exists in South Africa, can cause the burden of influenza to be much greater than you would expect in a population with low HIV prevalence. For these reasons, HIV became one of the most influential risk factors for which we controlled in our study.

An important aim of the burden study in South Africa was to guide public health authorities in the country on how their policies regarding influenza vaccination can better meet the needs of their population. The HIV prevalence in South Africa, while varied between provinces, averages 17% in the 15-49 age group. It is crucial for public health officials to understand the disproportionate risk people in this age cohort have of developing severe influenza infections, and to develop policies and programs accordingly.  

My conversations about why I was researching influenza were both valuable learning and teaching opportunities for me. The devastating HIV epidemic in South Africa is inextricably linked to increased susceptibility of its population to concomitant infections, such as severe cases of influenza. Therefore, it is important that discussions of HIV and influenza overlap in order to reinforce in the public’s mind the relationship these diseases have with each another. I hope I was able to play a role – however small – in increasing this understanding.


Jillian Murray is a second year Master of Science in Public Health (MSPH) student in the Global Disease Epidemiology and Control program at Johns Hopkins Bloomberg School of Public Health.