Seeking to reduce flu in babies Living with AIDS # 482
Can vaccinating pregnant women against the flu protect their newborn babies from getting the influenza virus? Well, that’s exactly what a clinical study in three countries, including South Africa, wants to find out.
The intervention involves vaccinating pregnant women with the influenza vaccine in order to protect their babies against the flu virus. This is not as direct as vaccinating the baby itself. But researchers believe that this approach can yield a positive result.
‘When we give the mother the influenza vaccine, we expect her to develop antibodies to the vaccine. And when a person develops antibodies to the vaccine, what that means is that when they encounter the virus, they are protected against becoming ill from the virus because antibodies will sort of attack the virus and prevent the virus from making the person ill’, says Professor Shabir Madhi, Vaccinology professor at the University of the Witwatersrand.
‘What happens when the child is in the womb is that there are a number of different antibodies which are circulating in a mother’s blood which actually transfer across the placenta and into the child’s blood-stream. It actually gets sort of absorbed into the child’s blood-stream. And the very young infant ‘ the child under three months of age ‘ is largely dependent on those antibodies that he derives from the mother to be protected against a number of different bacteria and a number of different viruses. So, in this particular instance, what we’re really interested in is: Can we have the mother produce a sufficient amount of antibodies by vaccinating her with the influenza vaccine and, then, have those antibodies transfer over to the baby in a very passive way, and, hence, when a baby becomes exposed to the influenza vaccine, the baby, hopefully, will be protected against developing severe influenza illness?’, Prof. Madhi explains further.
If successful, the intervention can protect babies from the time they are born up to about four months of age.
‘We usually expect antibodies to provide protection to a child for, at least, three to four months after birth. In South Africa, as an example, of all the children that die’¦ almost a quarter of children that die will actually die in those first three to four months of age. And infection in those first three to four months of age is one of the most important causes as to why children are dying in that age group. So, what we’re hoping for this vaccine to achieve is to actually protect the child, at least, until four months of age. We don’t expect the child to be protected beyond four months of age because by that stage the amount of antibodies that remain in the child start diminishing and are not sufficient to actually protect the child against developing influenza illness’, says Professor Madhi.
Influenza is by no means the biggest killer of babies in the country, but it’s one of those viruses for which a preventative vaccine exists to avoid severe disease in babies. Professor Madhi believes that this intervention could work. A recent similar study in Bangladesh among a small sample of almost 400 women has shown encouraging results.
‘Children that were born to mothers who received the influenza vaccine were 50% ‘ 60% less likely to develop influenza illness compared to children that were born to mothers that didn’t receive the influenza vaccine. So, we’ve got fairly good evidence from a very different setting that this is a strategy that might very well work’, he says.
In South Africa, over 1 000 pregnant women are already participating in the study. There will be around 4 500 women participating over three years. Other places where the study is being conducted are Mali and Nepal. The study in South Africa involves both HIV-positive and HIV-uninfected women.
‘In South Africa, unfortunately, we’ve got this huge burden of HIV infection in pregnant women and we need to know whether this particular strategy works if a woman is HIV-infected as well as if a woman is HIV-uninfected. So, we expect there might be differences in how well the woman responds to the vaccine, depending on whether they are HIV-infected or not. Individuals that are HIV-infected certainly develop more severe influenza illness than those that are uninfected. But in the context of this particular study, the additional important factor is how well these antibodies transfer from mothers to the babies and whether there are any differences between HIV-infected and uninfected women in relation to the amount of antibodies that successfully transfer over to the baby to protect the baby’, Professor Madhi concludes.