HEALTH: US Scientists Develop Typhoid Vaccine Safe Enough for Children

By Marwaan Macan-Markar Reprint | | Print |

Marwaan Macan-Markar

MEXICO CITY, Apr 29 2001 (IPS) - Scientists at a leading US health agency are confident about the prospects of their latest medical achievement: a new vaccine capable of protecting children between the ages of two and five against typhoid fever, a disease which kills close to 600,000 people every year.

This vaccine is more potent than the other typhoid vaccines currently in use, say the scientists from the National Institute of Child Health and Human Development (NICHD) in a report published in the recent issue of the New England Journal of Medicine. Tests have shown that the vaccine is 91.5 percent effective and that it is virtually free of side effects.

“We have a two-fold victory in world public health,” said Dr. Duane Alexander, director of the NICHD, in a press release. “Not only is this the first vaccine to protect young children against typhoid fever, it appears to be the most effective typhoid vaccine ever developed.”

According to the NICHD, based in Bethesda, Maryland, this achievement comes after extensive work conducted by its researchers in the Dong Thap province of Vietnam, where over 11,000 Vietnamese children between the ages of two and five were involved in the tests.

“The children received two injections, six weeks apart. Half received the vaccine, and the other half, a placebo,” it reveals. “The vaccine group had 47 cases, for an effectiveness rate of 91.5 percent. By comparison, typhoid vaccines currently on the market have a 70 percent effectiveness rate and do not protect children under age five against the disease.”

What is more, it adds, less than two percent of children experienced any side effects, “all of which were mild, and limited to swelling at the injection site, or to mild fever that resolved within 48 hours”.

According to the World Health Organisation (WHO), vaccines are currently regarded as the “only way of controlling typhoid fever”, consequently protecting those people living in endemic regions of the world and those travelling to such areas.

Despite the present availability of three different vaccines against typhoid, there are still issues to be addressed before incorporating them into large scale immunisation programmes, admits the Geneva-based health agency.

“The three currently licensed vaccines against typhoid fever are probably of comparable protective efficacy,” it affirms. “There is, however, a considerable difference in terms of side effects, ease of administration and price.”

Furthermore, it feels that two of the vaccines still need more tests before being given to children under five years old. “Although both Ty21a and Vi polysaccharide vaccines are safe and of acceptable efficacy in individuals above five years of age, further controlled studies on the respective value of these vaccines for large-scale vaccination of children below five years of age are encouraged.”

The need for such a medical intervention is urgent, it adds, given the global spread of typhoid, which originates in the intestines after swallowing the bacteria, known as Salmonella Typhi (S. Typhi), and which is “highly adapted to humans and has no other known natural host”.

“In most cases, S.Typhi is spread by faecal contamination of water supplies. This faecal-route of transmission is closely associated with poor sanitation and food hygiene,” a WHO study notes.

Consequently, the disease has resulted in “a substantial public health problem” in many parts of South and East Asia, Africa and South America, which lack modern sanitation facilities unlike the industrialised countries.

The WHO estimates that at least 16 million cases occur each year, “and of these approximately 600,000 end fatally”.

Furthermore, it states, severe forms of typhoid fever “may entail cerebral dysfunction, delirium and shock, and in 0.5-1 percent of the cases intestinal perforations and haemorrhages”.

Adding to that burden is the emergence of S.Typhi strains that have become resistant to the antibiotics prescribed for typhoid fever. “Antibiotic treatment of carriers and of typhoid fever in general has, in recent years, become more complicated by the emergence of resistant strains of S. Typhi,” says the WHO.

What prevails in Vietnam, in fact, illustrates such a reality, where about 90 percent of the strains are reported to be resistant to several antibiotics, including recently developed ones. “Inappropriate use of anti- microbial drugs will accentuate these problems,” the WHO says.

Multidrug resistant strains of typhoid have also been reported from other Asian countries, the Middle East and Latin America, adds the WHO.