Protecting the family to protect the child: vaccination strategy guided by RSV transmission dynamics.

Respiratory syncytial virus (RSV) is the most important respiratory pathogen of childhood and also contributes to substantial morbidity and mortality in the elderly. It was recently estimated that as a single infectious agent, RSV is second only to malaria as a cause of death in children between 1 month and 1 year of age [1]. In addition, the global impact as an adult pathogen has a comparable level of morbidity and mortality as influenza in the frail elderly [2, 3]. Further demonstration that RSV is a ubiquitous global pathogen is now reported in the prospective family cohort study performed by Munywoki et al and reported in this issue of the Journal of Infectious Diseases [4]. More than 80% of households with children experienced an RSV infection within the 6-month surveillance period, and RSV was detected in 64% of study infants (defined as <1 year of age). In about 50% of households, more than one person was infected, and repeat infections in the same individual from homologous or heterologous RSV subtypes within the same season were documented. Thus, transmission within family units is common, and natural infection with RSV, especially in very young infants, does not provide solid immunity against reinfection. These data that were collected in rural Kenya are consistent with another household study performed more than 40 years ago in Rochester, New York, that reported 2 months of surveillance data [5]. Although it would be useful to have more data from different geographic and climatic settings, the congruity of these 2 studies suggests the likelihood that these results are a realistic reflection of how RSV is transmitted within family units globally. Importantly, the current study was prospective, employed active surveillance, and used modern diagnostic techniques such as polymerase chain reaction (PCR) and viral isolate sequencing to confirm temporal transmission patterns. The investigators showed that transmission of an infant’s first RSV infection was most often attributed to school-age children in the household. This report exemplifies the importance of understanding the epidemiological details of how a contagious respiratory pathogen spreads within a community. Indeed, understanding transmission dynamics may be a key factor in defining strategies that can successfully protect infants from RSV infection. In addition to using this information to emphasize the importance of handwashing and avoiding large particle aerosol and fomite transmission, it may be useful to ask how understanding transmission dynamics can inform vaccine development strategies. In particular, we should explore the potential target populations for RSV immunization. Although there is no licensed vaccine for RSV prevention, there are several candidates in development, and at least 3 are currently being evaluated in clinical trials. One of the key decisions each developer has to make is which population should be targeted for vaccination to accomplish their objectives. Although considerations could range from market size to public health impact, or from reducing severe disease in young infants to reducing morbidity and mortality in the elderly, the primary objective of most vaccine developers has been to prevent or reduce disease severity in the very young infant. Peak age of hospitalization with RSV is between 2 and 3 months of age, and hospitalized infants are known to have a higher frequency of subsequent wheezing during childhood. Therefore, preventing severe RSV infection in young infants would not only have a direct benefit on primary disease but may also reduce the incidence of childhood asthma. This hope has resulted in a rare consensus among parents, clinicians, hospitals, public health officials, insurance companies, and marketing executives, who all agree that protecting this youngest age group is the top priority. Received 21 January 2014; accepted 22 January 2014; electronically published 12 February 2014. Correspondence: Barney S. Graham, MD, PhD, Vaccine Research Center, NIAID, NIH, 40 Convent Dr, MSC 3017, Bldg 40, Rm 2502, Bethesda, MD 20892-3017 ([email protected]). The Journal of Infectious Diseases 2014;209:1679–81 Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2014. Thiswork iswritten by (a) US Government employee(s) and is in the public domain in the US. DOI: 10.1093/infdis/jiu075