March 12, 2024
We are in the middle of a wave of whooping cough and measles, these infectious diseases are appearing more and more often in Europe. What else can we expect as a result of the declining vaccination rate against childhood diseases? Experts from Radboud university medical center provide an explanation.
To find Osama Bin Laden, the CIA had a local doctor from Pakistan go door to door in 2011, ostensibly for a vaccination campaign. Bin Laden was found, but this fake campaign had disastrous consequences: public confidence in vaccines declined enormously and the Pakistani government put much less energy into the vaccination program, which almost came to a complete standstill. In the following years, this led to a major spike in the number of polio cases in Pakistan, a disease that had previously been almost eradicated.
Contageous
This example shows that infectious diseases against which vaccines exist can quickly reemerge when vaccination rates drop. And that is currently happening worldwide, including in the Netherlands, where the percentage of children following the national vaccination program has now fallen below ninety percent. ‘At Radboud university medical center we are also confronted with diseases that we can prevent with vaccination,’ says pediatric infectious disease specialist Lilly Verhagen. ‘In addition, I see much more doubt and I get more questions about vaccines than before. This applies not only to parents of healthy children, but also to risk groups.’
In mid-February, the RIVM reported a wave of whooping cough in the Netherlands and the European ECDC published a threat analysis on measles, with outbreaks now in 40 of the 53 European countries. According to Marien de Jonge, professor of Infection and Immunity, this is a warning: ‘Measles and whooping cough are the most contagious diseases against which we vaccinate in the national vaccination programme, with R0 values of 12-18 and 15-17 respectively. They are therefore the first to emerge when vaccination rates decline and act as a kind of canary in the coal mine.’
Preventieparadox
Will we see slightly fewer infectious diseases such as polio and diphtheria in the Netherlands? De Jonge: ‘You need a vaccination rate of at least ninety percent to keep infections under control. If that percentage drops further, such infections may return. Still, I don’t think it will get that far. Because if there is a horrible outbreak of, for example, measles, which kills children, I expect the discussion will change and the vaccination rate will rise again. But it would be very bad if it had to get to that point.’
It is an intrinsic problem with vaccines: precisely because of their successful effect, it is no longer as clear as before what they protect us against. ‘Many people wonder why we vaccinate against diseases that do not occur in the Netherlands. But that is precisely thanks to the vaccines,” De Jonge explains. ‘The effect of a therapy or medicine on complaints is much clearer. We also call this the prevention paradox. It also plays a role in communication about vaccines feature positive effect a role, as recently demonstrated by Radboud University. This means that people remember much better what does happen than what is prevented.’
The measles
Dutch hospitals are now expecting a possible outbreak of measles. Specialists do not wonder if the outbreak will happen, but when. A problem with measles is that babies only receive the first MMR vaccination at the age of fourteen months, which protects very well against measles. They are therefore not protected before that. This is not a problem with a high vaccination rate, but if it drops and the measles virus starts circulating, babies who have not yet been vaccinated are also at greater risk.
For measles, a vaccination provides much better protection than a previous infection. ‘Various studies have shown that the measles virus can erase the memory of the immune system,’ De Jonge explains. ‘Not only the memory cells against measles, but also memory cells against other diseases are destroyed. After an infection with measles you are more susceptible to other infections.’
Whooping cough
Whooping cough is currently already an official epidemic in the Netherlands. Whooping cough is not caused by a virus, but by a bacteria. The vaccine does not protect very well against spread, and therefore the bacteria always circulate to a greater or lesser extent. Eighty to ninety percent of 18-year-olds have come into contact with the bacteria. The vaccine protects very well against becoming ill.
Babies receive the whooping cough vaccination at the age of two months. This is because babies are very vulnerable to whooping cough, especially in the first weeks to months of their lives, and can also die from it. “Fortunately, pregnant women can now be vaccinated in the third trimester of their pregnancy,” says vaccinologist Dimitri Diavatopoulos. ‘The baby is then protected immediately from birth and can then skip a vaccination. We see that not all midwives and therefore also pregnant women are well informed about this.’ Currently, approximately seventy percent of pregnant women follow this new advice. Their babies are therefore protected against whooping cough immediately after birth, even if vaccination rates continue to decline.
Broader protection
In addition to outbreaks of infectious diseases that have almost disappeared in the Netherlands, less vaccination also has another effect. Evidence is mounting that vaccines not only provide specific protection against the disease for which they are designed, but provide broader protection. ‘BCG, OPV and MMR have already been shown to reduce child mortality further than you would expect based on their specific mechanism of action,’ says Professor of Experimental Internal Medicine Mihai Netea. ‘And we also see that effect in recent studies with the new vaccines against malaria and herpes zoster.’
This broader protection works through so-called trained defenses. Cells of the innate immune system are activated in such a way that they also respond more strongly to new infections against which the vaccine was not intended. Epidemiological data suggest that this effect may last for approximately two years after vaccination, thus reducing infant mortality. In a publication at the beginning of 2024, Netea unraveled how the vaccine against mumps, measles and rubella (MMR) achieves this trained defense: this involves activation of a certain type of T cells, which then take action against an unknown type of intruder. This broader form of protection also declines if the vaccination rate continues to decline.
Also read the five questions about measles to Matthew McCall. Or visit the RIVM website for more information the measles in whooping cough.
This is the recent publication described in The Journal de Clinical Investigation: MMR vaccination induces trained immunity via functional and metabolic reprogramming of γδ T cells, Rutger J. Röring, Priya A. Debisarun, …, Yang Li and Mihai G. Netea.
2024-03-12 10:02:28
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