Scientists believe a dengue infecton may protect against the coronavirus, as parts of Brazil where large numbers of people recently caught the mosquito-borne disease had fewer cases of COVID-19 than other parts of the country. However, experts in virology and immunology told Newsweek they weren’t convinced by the study.
The hypothesis emerged after scientists explored what different factors affected the spread of COVID-19 in the first six months of Brazil’s outbreak, which started in late February. Brazil is among the countries worst affected by the coronavirus, ranking third in cases—at over 4.5 million of the 31.6 million global total—and second for deaths—at 138,105 of a total 970,934—according to Johns Hopkins University.
The study was submitted as a what is known as a pre-print to the website MedRxiv, meaning it has not been through the rigorous peer-review process required to publish in a scientific journal. The authors plan to submit the work to a journal, Reuters reported.
The researchers looked at data on coronavirus and dengue in Brazil, as well as 2019 population size estimates for each of the country’s 5,570 municipalities.
Areas where there were large concentrations of dengue fever cases during the epidemic of 2019/2020 had a “scarcity” of COVID-19 cases and fewer deaths, the team found. The outbreaks in these areas also developed more slowly. The correlation grew until reaching a peak around July 1, 2020. When the team repeated their analysis for the mosquito-borne disease chikungunya, which is also endemic in Brazil but at much lower levels, they did not find a similar correlation with COVID-19 cases, suggesting something special was happening with dengue.
The team looked for similar patterns in 15 countries where dengue is prevalent, and found the more dengue fever cases regions had in 2019/2020, the fewer COVID-19 cases they had by July 2020.
At the same time, a “sudden decline in dengue cases” in March 2020 which officials pinned to underreporting during COVID-19, may be explained by the coronavirus infecting an individual, meaning they would not catch dengue, the team said.
It is well known that immunity to one germ can sometimes confer immunity to another, even between unrelated species in some cases, according to the authors. As between 100 to 400 million people around the world catch dengue each year “this finding could have a significant impact on the management of the current SARS-CoV-2 [coronavirus] pandemic,” the team said.
“Clearly, further epidemiological and immunological studies will be needed to test this hypothesis,” they wrote.
Future studies could explore whether a dengue vaccine, or for one of its close relatives, could protect against the coronavirus.
Co-author Miguel Nicolelis, a professor of neuroscience at Duke University, told Reuters the findings are interesting because people carrying dengue antibodies in their blood have been known to test falsely positive for COVID-19 coronavirus antibodies despite not being infected.
“This indicates that there is an immunological interaction between two viruses that nobody could have expected, because the two viruses are from completely different families,” Nicolelis told the news agency.
Experts who did not work on the study and spoke to Newsweek viewed the study with caution.
Ian Jones, professor of virology at the U.K.’s University of Reading told Newsweek the team presented no direct evidence to suggest that dengue infection provides a level of protection against the coronavirus when the two are not related.
Jones said the team were mistaken to speculate that a dengue vaccine might be useful for protecting against the coronavirus, as only one is licensed but not widely used “and far better ‘real’ vaccines against SARS-CoV-2 [the coronavirus] will be available soon.”
Prakash Nagarkatti, vice president of research at the University of South Carolina’s department of Pathology, Microbiology and Immunology, told Newsweek the study raises “exciting” questions but more research is needed to test the hypothesis.
“I would not support the suggestion of authors that [a] dengue vaccine be used against COVID-19 before we do further studies and fully understand the mechanism. Moreover, [the] Dengue vaccine has had [a] lot of safety concerns that it may make some people become more susceptible to a severe form of infection.”
Al Edwards, associate professor in biomedical technology at the U.K.’s University of Reading, told Newsweek he did not want to dismiss the study that may have made an important finding.
But he said “it’s not especially likely that dengue ‘protects’ against COVID-19, they are quite different viruses and there is no immunological mechanism that is well understood that would facilitate such cross-protection.”
It is likely that a person who has recently recovered from an infection. “has a ‘heightened defence level’ against other bugs, in a very general way. But this wouldn’t explain the observations in this study.”
He went said: “Immunologically speaking, there would be no mechanism whereby a dengue vaccine could protect against COVID-19- that’s just not how vaccines work.”
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