Babies have more protection against some diseases (e.g. whooping cough, tetanus) in the first few months of life if their mothers are vaccinated during pregnancy. Vaccines given to mothers produce antibodies that fight disease. These 'maternal' antibodies are passed on to babies before birth and protect them whilst they are too young to be vaccinated themselves.

Naturally, over time, maternal antibodies in babies decline. It is therefore important that, at some point, babies receive their own vaccinations to keep them protected. Timing is important. If maternal antibodies still exist in babies when they receive their first vaccinations, they may have a lower antibody response. This may mean that they are not protected as well as they could be.

In planning vaccine programmes, therefore, it is important to understand how quickly maternal antibodies decline in babies.

Currently, there is little information about the rate at which maternal antibodies decline in babies for some common vaccines. Antibody levels may decline at different rates for different vaccines. Until we know more, it is difficult to find out the best time to vaccinate babies.

In their pump-priming project entitled 'Maternal transplacental antibody decay rates: an individual participant data meta-analysis,' Merryn Voysey from the University of Oxford and her team combined data from infants born to women taking part in studies across 9 countries (UK, Belgium, Thailand, Vietnam, Canada, Pakistan, USA, Guatemala and the Netherlands) to look at the way antibody in infants declines over time. Data from 1426 mother-infant pairs were available for the analysis. The half-lives of maternal antibodies for 6 different antigens were similar, ranging from 30 days for pertussis toxoid antibodies to 35 days for pertactin antibodies. The decay of maternal antibodies did not significantly differ by maternal age, birthweight, maternal vaccination status, or the type of vaccine administered.  

Maternal antibodies decay at different rates for the different antigens; however, the magnitude of the difference is small.