First author

More than 40 years after the first measles vaccine became available, the virus is still a leading cause of death in children in many countries. Aid organizations such as Médecins Sans Frontières (MSF) are finding that vaccination strategies that proved successful in developed countries do not always work for developing regions. On page 679, Matthew Ferrari, a postdoc at Pennsylvania State University, and his colleagues show that seasonal and cultural patterns drive predictable episodic outbreaks of measles in Niger's capital, Niamey. In this setting, vaccination can be beneficial during outbreaks — a tactic previously considered inappropriate given the disease's rapid rate of transmission. Ferrari spoke to Nature about his work and its impact on health policy.

Do organizations such as MSF typically reach out to academia?

No. MSF focuses solely on providing health care, and has little opportunity to critically analyse data. They first contacted me to examine data from their vaccination programme in Niamey to assess whether supplemental vaccination in response to outbreaks might be beneficial.

What challenges did you face when modelling measles outbreaks?

Niger has one of the highest birth rates in the world, so there is a rapid build-up of children who are susceptible to measles. This makes it hard to determine the critical percentage of people that need to be vaccinated to head off an outbreak. MSF has a good relationship with the Niger Ministry of Health, and they granted us access to 20 years worth of measles incidence rates. Using these data, we showed that the classical dynamics of virus infection and spread do not hold up in Niger.

What unexpected dynamics did you find?

In Niger, the median age of measles infection is two years, whereas it is between five and six in European and North American countries, where children are socially protected until they enter school. We also found that the incidence of measles declines once the rainy season begins — presumably because the city's population falls when people return to agriculture after the dry season. We are now looking at satellite imagery to better understand how changes in population density affect disease transmission.

Has this work changed your career goals?

Yes. I now want to work at institutions with strong public health connections. I like the rapid interplay between data gathering and critical evaluation of health policy, because I think it keeps scientists accountable — a strong motivator to do good work.