Targeted vaccination mainly concerns children and adults with comorbidities. Although they aim to protect the most vulnerable populations, they are considered too restrictive by several experts and organizations consulted during the public consultation.
A worrying context in overseas territories
Dengue fever, a viral disease transmitted by mosquitoes of the genus Aedeshas become a major problem in overseas departments and regions, with a succession of epidemics in recent years.
In Guadeloupemore than 13 000 cas were recorded between January and July 2024, according to health authorities, leading to more than 200 hospitalizations and several deaths. The last epidemic ended in July 2023, but a new epidemic phase was declared in November 2024. Reunionbetween 2018 and 2023, there are more than 65,000 confirmed cases which have been reported, testifying to continued viral circulation.
This resurgence imposes a strong pressure on local health systemsparticularly during peak epidemic periods. In the Antilles and Guyana, children and adults are the most affected. On the other hand, at Mayotte and Reunionthese are mainly the adults who develop serious forms, often aggravated by comorbidities such as diabetes or hypertension.
If dengue fever remains asymptomatic in 50 to 90% of casesit evolves towards severe forms in approximately 5% of symptomatic cases. These severe forms can be fatal, especially in people immunocompromised or suffering from chronic illnesses such as sickle cell anemia and thekidney failure.and 2?
Individual rather than collective vaccination
HAS recommends the use of the Qdenga vaccine in the French territories of America (Antilles and Guyana), as well as in Mayotte and Reunion. Two priority populations are targeted:
- Children aged 6 to 16 with a history of dengue infection;
- Adults aged 17 to 60 presenting comorbidities, with or without a history of infection.
This targeted approach is based on a careful benefit-risk analysis. HAS justifies its choices by several elements:
- A lack of solid data in HIV-negative people : in clinical trials, the Qdenga vaccine did not demonstrate effectiveness against certain serotypes (DENV-3 and DENV-4) in people who have never been infected. HAS emphasizes that the use of the vaccine in these populations could present a theoretical risk of ADE (Antibody-Dependent Enhancement), a phenomenon where antibodies facilitate infection rather than fighting it.
- Variable effectiveness depending on serotypes : the vaccine displays protection ranging from 51.8% against DENV-3 has 80.2% against DENV-2 for symptomatic dengue. Severe forms could not be evaluated due to lack of sufficient data.
- Priority to populations at risk : by targeting children with a history of infection and adults with comorbidities, the HAS aims to protect the most vulnerable groups, by reducing the risk of hospitalization and mortality in overseas territories.
The recommended scheme includes two doses spaced 3 months apartoutside of epidemic periods. After a dengue infection, a period of 6 months is recommended before vaccination.
HAS underlines the need for reinforced clinical monitoring for certain populations, such as vaccinated children with sickle cell disease. The vaccine remains contraindicated in immunocompromised individuals, pregnant and breastfeeding women.
Finally, she insists on the need to maintain the individual protection measures against mosquitoes (repellents, mosquito nets, covering clothing) to strengthen the fight against dengue fever.
A scope of application considered too restricted
In its recommendations, the HAS targets vaccination for children 6 to 16 years old with proof of dengue infection and for adults with comorbidities. But this choice is strongly criticized. Several experts warn about the character too restrictive of these recommendations, which could limit their impact:
In practice, the evidence of previous infection required by the HAS is deemed impracticable in the territories concerned. Takedathe laboratory manufacturing the Qdenga vaccine, warns:
“Many people are unaware of their HIV status. The requirement for documented proof does not take into account the realities on the ground, where more than 75% of infections are asymptomatic. ».
Specific needs for populations at risk
Current recommendations ignore certain particularly vulnerable groups, including adults with comorbidities and the sickle cell patients. The COVARS alert on this point:
“It appears essential to make a specific recommendation for the sickle cell population in the French American territories, in both children and adults. ».
Likewise, the Martinique University Hospital Center notes that the children with sickle cell disease require special attention:
“The benefits of vaccination for children with sickle cell disease do not appear to be sufficiently emphasized… Their regular monitoring would, however, allow for easy inclusion in longitudinal studies. ».
Expand vaccination for collective impact
Another major criticism concerns the absence of a collective vaccination strategy. The SPILF underlines that restricting access to a small group does not sufficiently reduce viral circulation:
“Wider vaccination coverage would have major benefits: ‘herd’ effect and reduced risks of saturation of health systems in hyper-endemic periods. ».
These criticisms are echoed in the international experiences :
- In Brazilwhere dengue is endemic, health authorities have recommended vaccination with Qdenga for populations up to 39 ans in the most affected regions. This approach was justified by the need to protect the adolescents and young adultsoften exposed and at greater risk of serious complications.
- In Argentinea similar strategy was adopted, with an expansion of vaccination to wider groups to include people with comorbidities and populations residing in areas with high transmission.
These examples show that a vaccination not limited to HIV status or restricted age group can help reduce viral circulation and indirectly protect the most vulnerable populations.
Furthermore, theOMS encourages an inclusive approach in endemic areas:
“The WHO recommends vaccination without restrictions linked to the serological status of patients, in areas where dengue is a threat to public health. ».
Wider vaccination coverage could:
- Reduce the circulation of the virus by creating a “herd” effect, beneficial for all populations.
- Relieve health systems which are struggling to manage epidemic peaks, particularly in pediatrics and adult medicine.
- Meet the specific needs of adults at riskas recalled by COVARS :
“It is essential to protect adults from serious forms linked to comorbidities such as diabetes and renal failure, particularly observed in Reunion Island. ».
Vaccine acceptability in danger
The complexity of the eligibility criteria and the overly narrow targeting also risk harming the support of the populations local. The French Society of Travel Medicine (SMV) with a whisk:
“The vaccine eligibility criteria raise questions due to their restrictive nature… This risks fueling public mistrust of a vaccine which could nevertheless be a major tool against dengue fever. ».
The Martinique CHU goes further by emphasizing that broader recommendations, associated with a pre-epidemic strategycould have avoided deaths:
“A recommendation for reactive vaccination in the pre-epidemic period would seem appropriate to me in the event of DENV-2 circulation. This could have prevented deaths. ».
To convince and adjust the strategy, several actors are calling for:
- Real-life Phase IV studies to evaluate the effectiveness of the vaccine against serotypes DENV-3 and DENV-4.
- A rigorous monitoring of adverse effects in vaccinated populations, particularly adults and children with sickle cell disease.
Towards a more ambitious strategy?
The HAS recommendations, although important, have attracted major criticism from experts and health professionals. Their overly restrictive nature – both in terms of targeted populations and eligibility requirements – limits their reach even as dengue fever continues to weigh heavily on overseas territories.
As highlighted in the SPILF :
“Dengue fever is a major public health problem…Such restrictive recommendations limit their impact on reducing hospitalizations and deaths. ».
Faced with a succession of epidemics affecting increasingly vulnerable populations, it appears essential to:
- Extend vaccination to adults at riskby aligning the French strategy with the more inclusive WHO recommendations;
- Include Indian Ocean territories such as Reunion and Mayotte, regularly affected by intense epidemic waves;
- Simplify eligibility criteriaby abandoning the requirement for proof of previous infection, difficult to establish in contexts of high viral circulation.
By relying on the successful international experiences (Brazil, Argentina) and taking into account the local realitiesa more ambitious vaccination strategy could significantly reduce the burden of dengueprevent hospitalizations and save lives.
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