Knockout jab

FEW vaccines have been so successful, so quickly, as MenAfriVac. It was introduced into Africa in 2010, to immunise people against meningitis A—a bacterial infection of the membranes surrounding the brain and the spinal cord, which can cause death or brain damage within hours of the onset of its flu-like symptoms. Since then, the caseload of the illness has plummeted to zero in 16 countries that used MenAfriVac in mass vaccination campaigns. Before the vaccine’s introduction epidemics in the “meningitis belt”, which stretches from coast to coast south of the Sahara desert (see map), used to kill thousands a year and disable many more, nearly all of them children and young adults. In 1996, for example, an outbreak killed 25,000 people and sickened 250,000 in six months.

Out of sight is, however, all too frequently out of mind, and health experts now worry that this one-off success will not, at least in some countries, be followed by the introduction of MenAfriVac into routine schedules of infant vaccination. A study just published in Clinical Infectious Diseases by Andromachi Karachaliou of Cambridge University and her colleagues shows what this could lead to. Ms Karachaliou’s computer model predicts that the epidemics will return with a vengeance in about 15 years if MenAfriVac does not become a routine childhood jab, as the World Health Organisation (WHO) recommends it should. That, the model suggests, is the moment when waning immunity among those already vaccinated, and no immunity at all among a rising generation of the unvaccinated, could combine with seasonal factors (epidemics usually start in the dry season) to create a crisis.

In principle, universal vaccination could eradicate the disease, for the bacterium that causes it can survive only in humans and vaccination clears it from its hosts. The current goal, however, is less ambitious: to stop the epidemics in all 26 countries of the belt, including the ten which have yet to roll out the one-time mass-vaccination campaigns that have done so much good elsewhere. These campaigns cover only those aged between one and 29. That is, nevertheless, about 70% of Africa’s population—and this, combined with the fact that older people are much less infectious and rarely succumb to the disease, is enough to create “herd” protection, according to Marie-Pierre Preziosi, a meningitis expert at the WHO. Herd protection is the point at which, even though vaccine coverage is not 100%, there are insufficient infectible people around for the disease to sustain itself.

To keep a proper lid on meningitis A, though, the next step should be to make vaccination routine for infants and remain vigilant for outbreaks. Gavi, an international vaccine fund for poor countries, has already promised its backing for this plan. Besides saving lives, such an approach would save money. A second paper in Clinical Infectious Diseases, describing a study led by Anaïs Colombini of the WHO, looked at how routine vaccination might play out in Burkina Faso. Ms Colombini concluded that such a pre-emptive approach would cost less than the alternative of waiting for an outbreak and then vaccinating en masse. This would probably be the case in other countries of the belt, too.

Moreover, MenAfriVac brings benefits beyond curbing meningitis, as two further studies published in the same journal show. These looked at its effect on tetanus. The MenAfriVac uses tetanus toxoid as the protein to which the immunity-generating antigen is attached. Other vaccines that employ a similar trick are known to boost immunity to tetanus. In one of the studies, Nicole Basta of the University of Minnesota and her colleagues have shown that this process works for MenAfriVac, too. Their research, carried out in Mali, found that the mass campaign increased the share of people with long-term tetanus immunity from 20% to 59%. This makes MenAfriVac a formidable tetanus booster, even though it is not strong enough to stand alone against tetanus, says Dr Preziosi.

What this means for neonatal tetanus, which kills nearly 50,000 newborns a year in sub-Saharan Africa, is shown by the second study, led by Ray Borrow of Manchester Royal Infirmary, in Britain. Poor countries now tackle it by giving pregnant women tetanus boosters, which ensure they pass antibodies on to their unborn babies. Dr Borrow’s team found that rates of neonatal tetanus fell by 25% in countries that had had a MenAfriVac campaign. Although some of this drop may have happened for other reasons, the evidence points mostly in the direction of the vaccine’s hefty double-duty.

All of this makes MenAfriVac one of the brightest public-health stars around. For, if countries in the meningitis belt follow the prescription these studies suggest, they should be able, quickly, to put the lid on two scourges for the price of one.