Two often-neglected pathogens cause as much child mortality as HIV, malaria, and tuberculosis combined, researchers said.
In companion papers in the Sept. 12 issue of The Lancet, scientists reported that the mortality associated with Streptococcus pneumoniae and Haemophilus influenzae type b (Hib) reached about 1.2 million among children younger than five in the year 2000.
The findings are "shocking" because safe, effective vaccines are readily available, according to Igor Rudan, MD, and Harry Campbell, MD, both of the University of Edinburgh Medical School.
In an accompanying editorial, they said research and development into diseases such as HIV and malaria has benefited from years of advocacy, while such conditions as pneumonia, meningitis, and diarrhea "have attracted less international attention and support."
Yet, they argued, the disease burden among children under five is much the same despite the availability of vaccines against the two pathogens that have been shown to be "consistently safe and effective" in trials in the developing world.
The two studies - performed by the Hib and Pneumococcal Global Burden of Disease Study Team - reveal for the first time the extent of the mortality caused by S. pneumoniae and Hib, Rudan and Campbell said.
In both studies, researchers used clinical trial data, country statistics, literature searches, and other data to estimate the proportion of child deaths associated with each pathogen.
Globally, they found, 10.6 million children under five died in the year 2000.
In that year, about 14.5 million episodes of serious disease caused by S. pneumoniae were estimated to occur, according to Katherine O'Brien, MD, of the Johns Hopkins Center for American Indian Health in Baltimore, and colleagues.
Those episodes led to about 826,000 deaths, including 91,000 in HIV-positive and 735,000 in HIV-negative children, O'Brien and colleagues concluded.
The pathogen is thus responsible for about 11% of all deaths in the under-five age group, they said, if deaths among HIV-positive children are excluded.
Also in 2000, Hib caused about 8.13 million serious illnesses worldwide, according to James Watt, MD, also of the Johns Hopkins Center, and colleagues.
Those cases ended in death 371,000 times, they said, including 8,100 in HIV-positive and 363,000 in HIV-negative children.
That rate works out to about 3.5% of all deaths in the age group.
In comparison, the World Health Organization estimated in 2005 that HIV/AIDS caused 3% of such deaths and malaria 8%, with TB as part of a general category of other causes that totaled 10%.
It is likely, the researchers said, that the mortality rates associated with the two pathogens are under-estimated.
The effect of vaccines can be seen from figures comparing countries where they are widely used to those where they are either not available or not widely used, O'Brien and colleagues said.
By August 2008, 24 high-income and two middle-income countries had routine pneumococcal conjugate vaccination, but there were none in Africa or Asia, they said.
In 2000, those 26 countries accounted for less than 0.2% of deaths caused by S. pneumoniae, and the risk of death caused by the pathogen averaged 1.5 fatalities per 100,000, versus 58 per 100,000 in countries where the vaccine was not in use, the researchers said.
The Hib vaccine, on the other hand, is making inroads, Watt and colleagues said, with 108 countries representing more than 55% of the world's children now routinely vaccinating the young.
Despite progress, Rudan and Campbell argued, "current immunization coverage with these vaccines is a striking example of global inequity."
Children in countries that don't use the vaccines have about 40 times the risk of dying from pneumococcus or Hib than children in countries that use them routinely, they said.
The S. pneumoniae study was supported by the GAVI Alliance and the Vaccine Fund. The researchers reported no conflicts.
The H. influenzae type b study was supported by the GAVI Alliance and the Vaccine Fund. The researchers reported no conflicts.
The editorialists said they had no conflicts.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
The LancetSource Reference: O'Brien K, et al "Burden of disease caused by Streptococcus pneumoniae in children younger than 5 years: global estimates" Lancet 2009; 374: 893-902.
The LancetSource Reference: Watt J, et al "Burden of disease caused by Haemophilus influenzae type b in children younger than 5 years: global estimates" Lancet 2009; 374: 903-11.
The LancetSource Reference: Rudan I, Campbell H "The deadly toll of S. pneumoniae and H. influenzae type b" Lancet 2009; 374: 854-856.