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Massive doubts about dengue fever vaccine effects

Massive doubts about dengue fever vaccine effects

Dengue vaccine apparently not the celebrated breakthrough

After a study on a possible vaccine against dengue fever was published in the specialist magazine "The Lancet", the French pharmaceutical company Sanofi Pasteur is already celebrating its development as a breakthrough. However, numerous media reports point to the weaknesses of the vaccine and the study authors have only found an effectiveness of up to 30 percent. Apparently, the misinterpretation of the study results on the part of the group should make sales possible.

The dengue virus has spread more and more worldwide since the 1970s. The four different types of dengue virus, which originally only occurred in a limited space, are now widespread in large parts of South Africa, Southeast Asia, India and South and Central America. In the south of the USA and the north of Australia, too, more and more people are suffering from dengue fever. The cause of the growing virus spread is global travel and climate change, which enables the tropical vector mosquitoes of the dengue virus to open up larger habitats. The options for treatment and prevention have so far been extremely limited. There are no special drugs for dengue or a vaccine. Only an effective mosquito repellent, with mosquito nets, body-covering clothing and anti-mosquito repellents, is suitable for prevention. Major pharmaceutical companies such as GlaxoSmithKline, Inviragen, Merck and Sanofi Pasteur have been working on the development of a vaccine for years - so far without success. In the end, the study that is currently being hailed by Sanofi Pasteur also comes to no other conclusion.

Up to 100 million dengue fever diseases per year
According to estimates by the World Health Organization (WHO), up to 100 million people worldwide develop dengue fever every year. According to the WHO, the number of illnesses has doubled in the past ten years. Infection occurs via mosquito bites, with the Egyptian and Asian tiger mosquitoes being the most common carriers. After a maximum of two weeks of incubation, dengue fever manifests itself in symptoms such as fever, chills, severe headache, muscle and limb pain. It is not uncommon for the disease to be accompanied by an itchy rash (rash). They usually resolve symptoms after a week at the latest. In rare cases, however, dengue fever takes a significantly more severe course. Hemorrhagic fever threatens with internal bleeding, vomiting blood, tarry stools, cerebral seizures and circulatory breakdowns (shock). Such a course of dengue fever can also lead to a coma or, in the worst case, to the patient's death.

Severe course of the disease with a second infection The risk of a severe course of the disease is particularly high with a second infection with the dengue virus. Although the organism has developed antibodies against the type of virus that the patients were already ill with, a new infection usually starts from one of the three other types of dengue virus. The immune system or the antibodies from the first infection are overwhelmed by the changed form of the virus. There is a risk of misguided reactions and particularly serious illnesses. On the one hand, this aspect is particularly critical for children who carry antibodies passed on from their mothers, but it also makes it difficult to find a suitable vaccine. Because the vaccine would have to act equally against all known dengue virus types in order not to provoke any particularly serious course of the disease. Otherwise, people who are vaccinated may become more ill than people who have no dengue antibodies at all. Sanofi Pasteur's supposedly positive news that a serum was developed for the first time that protects against three out of four dengue virus types is actually an argument against the vaccine. Because the vaccine offered no protection against the fourth type of virus.

Doubtful effectiveness of the dengue fever vaccine The statement on the effectiveness of the vaccine is more than risky given the protective effect of a maximum of 30 percent found in the current study. Other vaccines have already been withdrawn from the market with a significantly higher effectiveness because they did not offer adequate protection. To test the Sanofi Pasteur vaccine, researchers from Thailand, France, and the United States had injected more than 4,000 Thai school children between the ages of four and eleven years of age, injecting the serum or placebo and then observing the frequency of the subjects with dengue for two years Fever. 2,669 study participants received the vaccine, 1,333 served as a control group.

45 children fall ill despite vaccination According to the study authors, Prof. Arunee Sabchareon from the Institute of Pediatrics at the Mahidol University in Bangkok and Dr. Derek Wallace, working for Sanofi Pasteur in Singapore, during the study period with dengue fever. Four study participants suffered a dangerous secondary infection. The vaccine group accounted for 45 diseases. According to the researchers, this results in an efficiency of up to 30 percent. The vaccine was well tolerated and showed no serious side effects, said Wallace and colleagues. "This data shows for the first time that a safe vaccine against dengue fever is possible," write scientists in the current article.

Criticism of the pharmaceutical company's success reports The head of the diagnosis of viral diseases at the Bernhard Nocht Institute for Tropical Medicine in Hamburg, Dr. med. Jonas Schmidt-Chanasit was extremely skeptical about “ZEIT Online”, given the current success stories from the pharmaceutical company Sanofi Pasteur. "In reality, there was no significant difference between the vaccinated children and the control group," criticized Schmidt-Chanasit. Other vaccines with an effectiveness of 40 to 60 percent were withdrawn from the market because the protective effect did not meet the current requirements. In addition, even if the effects against all four dengue virus types were higher, there would still be a residual risk, since other virus variants can occur. Only recently has it been "more closely researched which dengue viruses are in circulation among monkeys," explained Schmidt-Chanasit. These could also be transmitted to humans by mosquitoes, which could trigger the risky effect of a second infection with extreme defense reactions of the organism in the vaccinated.

Mosquito repellent the best dengue prevention The study authors were not only concerned with proving the effectiveness of the dengue vaccine, but also with the safety of the vaccine. They rated it as a major success that the vaccine was well tolerated and that the effect of a dangerous secondary infection was not observed in any vaccinated child. According to the researchers, the vaccine group showed no serious illnesses or increased hospital stays. The vaccine is now to be tested in a large phase 3 study involving 30,000 volunteers in South America and Asia in order to obtain further data. The critics say that the long-term risk of side effects should also be examined more closely, since a two-year trial period hardly allows any statements to be made about the long-term consequences of the vaccine. Dr. Schmidt-Chanasit, who specializes in the rapid diagnosis of dengue fever as a motion sickness and researches the risk of transmission by native mosquito species, explained that mosquito repellent remains the best preventive measure against dengue fever. The research currently being carried out in Australia to combat the mosquito mosquitoes with infiltrated bacteria was "a very important approach without which dengue cannot be contained," the expert told ZEIT Online.

Spread of dengue fever in Germany Although dengue fever is currently an exception in Germany, the number of infections has also increased significantly in Germany over the past ten years. The Robert Koch Institute in Berlin reports almost 400 illnesses in 2010. In 2001 the number was 60 infections. Dengue fever is usually brought along as a motion sickness, but the carrier mosquitoes have also spread more and more in Germany in recent years. As long as the dengue virus is not yet widespread in the population, it cannot be transmitted by the mosquitoes. However, Dr. Schmidt-Chanasit to consider that once the pathogens have established themselves in the mosquito population, they are passed on to the offspring via the eggs. According to this, a further increase in dengue infections can be expected in the coming years. The pharmaceutical companies are in for a profitable business, so that hasty reports of success have to be assessed against this background. (fp)

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Author and source information

Video: Creation of a Dengue Vaccine. Jordi Esparza. TEDxTanglinTrustSchool (September 2020).