Could an RSV vaccine reduce childhood pneumonia in Africa?
Pneumonia is the leading cause of childhood death in sub-Saharan Africa and while it is well known that many pneumonias are caused by bacteria such as Streptococcus pneumonia – for which vaccines are available – we know less about those caused by viruses.
A new study, published in the Journal of the American Medical Association (JAMA), shows that Respiratory Syncitial Virus (RSV) is the most common cause of viral pneumonia in an area of rural Kenya. The researchers from the Kenya Medical Research Institute (KEMRI) and their colleagues suggest that vaccinating against RSV could reduce cases of pneumonia in children in the region.
The team studied the respiratory viruses found in 759 infants and children (aged between 1 day to 12 years old) who were admitted to Kilifi District Hospital with severe pneumonia during 2007. RSV was the most commonly detected virus, present in 34 per cent of cases with severe pneumonia, and in 42 per cent of the infants under one year old. They found other respiratory viruses in 29 per cent of admissions, with Human coronavirus 229E being the most common (6.7 percent), followed by influenza type A (5.8 per cent), Parainfluenza type 3 (3.8 per cent), Human adenovirus (3.8 per cent), and Human metapneumovirus (3 per cent).
To check that the presence of RSV was associated with pneumonia, the researchers also compared the results with those from infants and children with mild upper respiratory tract infection, and healthy children who had come to the hospital for immunisation. They found RSV in just 5 per cent of the healthy participants. Additionally, the other viruses were as common in healthy children as those with pneumonia.
The results therefore suggest that RSV is strongly associated with severe pneumonia and that it is the most common identified cause in this setting. Previous studies, over 2002–2007, had found RSV present in 15 per cent of severe pneumonia cases in the Kilifi population, increasing to 27 per cent during epidemic periods. This leads to estimates for the incidence of RSV in infants of 0.99 per cent per child per year (and 0.27 per cent for children under 5 years old) during 2006 and 2007. In contrast, the new study found twice that incidence during 2007, though this might be in part due to better diagnostic tools.
As a consequence of their studies, the researchers suggest that “the prevention of RSV-associated severe pneumonia might reduce all-cause clinically severe or very severe pneumonia admissions to the Kilifi District Hospital by one-third.” There are RSV vaccines suitable for infants in development, with one currently undergoing clinical trials.
However, before we get too carried away, it’s worth bearing in mind that this is still a small study involving less than a thousand people with monitoring for just a year and in a single location. It’s unclear whether the RSV-pneumonia relationship will be the same in other areas. The researchers are therefore calling for further studies like this over longer periods and in multiple settings in sub-Saharan Africa.
- Berkley, J., Munywoki, P., Ngama, M., Kazungu, S., Abwao, J., Bett, A., Lassauniere, R., Kresfelder, T., Cane, P., Venter, M., Scott, J., & Nokes, D. (2010). Viral Etiology of Severe Pneumonia Among Kenyan Infants and Children JAMA: The Journal of the American Medical Association, 303 (20), 2051-2057 DOI: 10.1001/jama.2010.675