In his address to Gavi, the Vaccine Alliance, the US Secretary of Health and Human Services referred to . He used that study to support his stance that . But what did the study say? How was it performed? What were its findings? And is that study, and others like it, enough evidence to stop using the vaccine?
We Know Vaccines Work, So What Was the Study About?
Vaccines are one of the most powerful tools we have in public health. They prevent deadly diseases like measles, , and pertussis (also known as ). The diphtheria--pertussis vaccine, commonly referred to as , has been a standard component of childhood immunization programs worldwide for decades. But in a hospital in , a group of researchers noticed something unusual that they thought was worth exploring more closely.
Between 2001 and 2008, . These were children between the ages of six weeks and about eight months. The researchers carefully noted whether each child had received the DTP vaccine, based on the vaccination card shown at the hospital. They were especially interested in whether there were differences in death rates between boys and girls who had or had not received the vaccine.
What Were the Findings?
What they found raised eyebrows. Among the children who had received the DTP vaccine, more girls died in the hospital than boys. But among children who had not received the vaccine, girls and boys had similar chances of survival. To clarify, the DTP vaccine continues to protect children from serious infections such as diphtheria and pertussis. But the researchers were concerned that there may be what they call “non-specific effects” (or NSEs). These are effects that are not directly related to the diseases the vaccine is meant to prevent. In this case, they wondered whether DTP might affect the immune system in ways that are different for girls and boys, which could lead to unexpected outcomes like higher mortality in certain groups.
The concept of non-specific effects is not new, but it remains a topic of controversy. Some vaccines, especially live vaccines like the measles vaccine or BCG (used against tuberculosis), have been shown to reduce deaths from other causes beyond the diseases they directly target. But for non-live vaccines like DTP, the picture is less clear. That’s why studies like the one from Guinea-Bissau are important. They raise questions that many people in global health might not have considered.
Should We Stop Using the Vaccine? No.
The findings from the study do not support the implication from anti-vaccine activists that we should stop using the DTP vaccine. The World Health Organization’s Strategic Advisory Group of Experts on Immunization (SAGE) has reviewed numerous studies on this topic. After reviewing all the available evidence, SAGE concluded that the DTP vaccine remains essential and safe. While they found that some studies reported adverse non-specific effects, especially in girls, they also pointed out that many of these studies were observational. This means that researchers did not randomly assign children to receive or not receive the vaccine.
In observational studies, there’s always a risk that something else is causing the pattern we’re seeing. For example, perhaps the sickest children didn’t receive vaccinations in time and died, so they were underrepresented in the sample. Alternatively, children from wealthier families may have had better access to vaccines and hospitals, underrepresenting children who were healthy and not hospitalized at all. These kinds of hidden factors (called confounding variables) can change the results in ways that are hard to detect.
But Didn’t the Researchers Think of This?
The Guinea-Bissau researchers tried to address some of these concerns, of course. The study is not a bad study from an epidemiological perspective. They adjusted their analysis to account for factors such as the child’s age, the mother’s education level, and whether the child had also received other vaccines, like BCG (a vaccine against tuberculosis not used in the United States). But even with those adjustments, the pattern of higher mortality among vaccinated girls remained. It wasn’t a huge difference, but it was enough to prompt them to call for further research.
This is where it gets tricky. We can’t conduct a randomized trial where some children don’t receive the DTP vaccine just to see what happens. That would be unethical because we already know that DTP prevents the onset and transmission of dangerous diseases. We couldn’t randomize a group of children into receiving no vaccine, because that would leave them vulnerable to potentially fatal diseases.
However, researchers can still investigate different schedules (such as whether administering other vaccines before or after DTP has an impact) or compare outcomes across various countries that follow slightly different immunization timelines. And they have. and does not significantly raise the risk of death in the children who receive it.
Where Are We Now? And Where Do We Go From Here?
For now, the World Health Organization continues to support DTP vaccination as part of its core childhood immunization schedule. And they are encouraging more studies that look into the timing and combinations of vaccines, especially in settings like Guinea-Bissau, where health systems are under strain and child mortality is high from all causes, especially infectious disease.
What this hospital study teaches us is not that DTP is bad, but that vaccines are powerful tools with complex effects. The more we learn about how they interact with the immune system and how those effects might vary by sex or other factors, the better we can fine-tune our immunization programs to save as many lives as possible. Public health is about asking hard questions, even about things we think we already understand. That’s how we move forward.
If you’re ever in a discussion about public health and vaccination, and someone asks whether all vaccines work the same for everyone, you can share this story and all its caveats. It’s a real-life example of how careful observation, even in a single hospital, can challenge our assumptions and help us ask better questions for the future.