While measles vaccination programs have been effective in reducing cases and deaths worldwide, large, unexpected measles outbreaks continue to occur, and research is needed to help inform additional immunization campaigns.
Justin Lessler, associate professor in the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health, and colleagues used mathematical models to assess the impact of vaccination campaigns launched in response to certain triggers. The triggers they tested included a threshold number of measles cases and the immune status – whether or not an individual is immune to measles – of people in a particular age group.
The findings, published in PLOS Medicine, suggest that monitoring population immune status and using this to trigger vaccination campaigns could reduce incidence and prevent the most severe epidemics across a range of settings. To learn more about the study and the significance of its results, I interviewed Dr. Lessler via email.
What drew you to study the epidemiology of infectious disease?
JL: I was working as a software engineer at IBM Research, and was looking for a change. While I liked solving puzzles in computer programming, I wanted to use my analytical skills to focus on larger scientific problems with a direct impact on people’s lives, so epidemiology seemed a natural fit. Problems in infectious disease epidemiology require a combination of empirical and methodological research, and include aspects of biology, sociology and epidemiology that I find fascinating.
Many people in high-income countries might assume measles vaccination to be a success story. Why is further research still required?
JL: There have been huge reductions in measles-associated mortality, and elimination of the virus in the Americas, over the past decade. However, while we have a safe and effective vaccine, measles remains a leading killer of young children worldwide and is stubbornly persistent in many parts of the world. There is room for biomedical innovation, but we should also explore new strategies to use the current vaccine more effectively. That was the focus of this work.
You modelled the potential impact of extra immunizations in populations, triggered by a threshold number of measles cases, or an age group’s immune status. Why were these chosen as indicators of the need for extra vaccination?
JL: Both are indicators that a measles outbreak might be on its way. An increase in cases is the most direct signal of an impending outbreak, and most countries already do some monitoring of measles cases. Blood tests that measure an age group’s immune status, on the other hand, can indicate the underlying risk of an outbreak, and we hoped that monitoring population immunity might warn of potential outbreaks before people actually start getting sick.
What do you see as the most important finding from your study?
JL: I think the most important messages of this paper are that campaigns triggered by both immune status and number of cases can be highly effective in avoiding unexpected, large epidemics, and this is true even when the coverage of such campaigns is relatively low. Another key message is that the optimal approach may vary significantly across different settings. Implementation requires international support and a nimble approach to public health to overcome political and practical challenges.
What impact do you hope your study might have, and what are the next steps for your research?
JL: I hope that this study inspires countries to strive for a higher level of awareness and responsiveness in measles control activities. In particular, I hope that it encourages countries and global health agencies to use blood testing surveys to track population immunity; especially where measles vaccination efforts have had some success in interrupting local transmission of the disease.
Research Article: Lessler J, Metcalf CJE, Cutts FT, Grenfell BT (2016) Impact on Epidemic Measles of Vaccination Campaigns Triggered by Disease Outbreaks or Serosurveys: A Modeling Study. PLoS Med 13(10): e1002144. doi:10.1371/journal.pmed.1002144
Image Credits: DFID – UK Department for International Development, Flickr; Justin Lessler