Pertussis exposure improves response to a booster vaccine

The Netherlands has vaccinated the population against whooping cough since 1957

Older children have more antibodies against the pertussis bacterium than younger children because they are more often exposed to the pathogen. They also show a stronger immune response after a booster vaccination against whooping cough. Exposure is therefore an important factor in the timing and effectiveness of vaccines. This appears from a publication by Radboudumc in Nature Communications.

The Netherlands has vaccinated the population against whooping cough since 1957. It is the ‘K’ in the DKTP vaccination, which children receive three times in their first year of life and again when they are four years old. Yet the bacteria that cause whooping cough are still around and making many people sick. This is because the vaccines protect very well against serious illness, but less well against infection with the highly contagious whooping cough bacteria.

What is the effect of the circulation of pertussis bacteria on a booster vaccination? That puzzled immunologist Dimitri Diavatopoulos and PhD student Janeri Fröberg from the Radboud University Medical Center. They examined two groups of children. ‘One group was between 7-10 years old, the other between 11-15,’ says Fröberg. ‘They had all had their series of injections from the National Immunization Programme. We gave them a booster and looked at the immune response in the nose, before the booster and a month and a year after that. In our measurements, we distinguished between antibodies against the vaccine and against the bacteria themselves.’

sick reports
The first thing that stood out was that the older group of children already had more antibodies against the pertussis bacteria in their noses than the younger group before the booster vaccination. “It could be due to exposure to the bacteria,” says Diavatopoulos. “Older children have had more time to come into contact with the bacteria themselves. But whooping cough outbreaks are often very local, so exposure can vary greatly by region and age group.’ To check this, the researchers delved into the regional data on whooping cough disease reports that the RIVM has made available. ‘We actually saw more sick leave due to whooping cough among the older group.’

Second, the researchers examined the response to the booster vaccination. Fröberg: ‘In the group with older children, we saw more antibodies in the nose against the vaccine and a slower decrease in antibodies from one month to one year after the booster. It is a very interesting find. This may mean that exposure to the pathogen leads to long-lasting antibodies in the nose after a booster vaccination and thus possibly protection against the disease. Conversely, a further vaccination without exposure may result in a less strong immune response.’

Insight
The degree of exposure to a pathogen appears to influence the response to a vaccine, with possible implications for the vaccination program. ‘Different countries vaccinate against whooping cough at different ages, and the number of booster vaccinations also varies,’ explains Diavatopoulos. “In the Netherlands, we give children a booster at the age of four, while in other countries, for example, it happens to children aged nine or twelve. In our vaccination program, that shot will soon also change, from four to six years old. Our study supports this subsequent administration of a booster. We must take into account the right balance between the circulation of the bacteria and the severity of complaints in people who become infected. A small exposure can be beneficial for the effect of the vaccination, but the disease burden must remain sufficiently low.’

That vaccines protect well against disease, but are less effective against spreading, is what we have heard more often in recent years. “We see parallels with the corona pandemic,” Diavatopoulos explains. “The immune response is also an interaction between vaccination and exposure. The sum of these factors affects how well a vaccine works and to what extent you are protected. For my part, we will take exposure into account in every study of a new vaccine, which will give us much more insight into protection.’

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