RIO DE JANEIRO • A new study that analysed the Covid-19 outbreak in Brazil has found a link between the spread of the coronavirus and past outbreaks of dengue fever, suggesting exposure to the mosquito-transmitted illness may provide some level of immunity against the disease.
The as-yet-unpublished study, led by Duke University's Professor Miguel Nicolelis and shared exclusively with Reuters, compared the geographic distribution of coronavirus cases with the spread of dengue last year and this year.
Places with lower coronavirus infection rates and slower case growth were locations that had suffered intense dengue outbreaks this year or last, the study found.
"This striking finding raises the intriguing possibility of an immunological cross-reactivity between dengue's Flavivirus serotypes and Sars-CoV-2," said the study, referring to dengue virus antibodies and Covid-19.
"If proven correct, this hypothesis could mean that dengue infection or immunisation with an efficacious and safe dengue vaccine could produce some level of immunological protection" against the coronavirus.
Prof Nicolelis told Reuters the results are particularly interesting because previous studies have shown that people with dengue antibodies in their blood can test falsely positive for Covid-19 antibodies, even if they have never been infected by the coronavirus.
"This indicates that there is an immunological interaction between (the) two viruses that nobody could have expected, because the two viruses are from completely different families," Prof Nicolelis said, adding that further studies are needed to prove the connection.
The study will be published ahead of peer review on the MedRxiv pre-print server and will be submitted to a scientific journal.
It highlights a significant correlation between lower incidence, mortality and growth rate of Covid-19 in populations in Brazil where the levels of antibodies to dengue were higher.
In states such as Parana, Santa Catarina, Rio Grande do Sul, Mato Grosso do Sul and Minas Gerais, which had a high incidence of dengue last year and earlier this year, Covid-19 took much longer to reach a level of high community transmission compared with states such as Amapa, Maranhao and Para that had fewer dengue cases.
The research team found a similar relationship in other parts of Latin America, as well as Asia and islands in the Pacific and Indian Oceans.
Prof Nicolelis said his team came across the dengue discovery by accident during a study on how Covid-19 had spread in Brazil, in which they found that highways played a major role in the distribution of cases.
After identifying certain case-free spots on the map, the team went in search of possible explanations. A breakthrough came when the team compared the spread of dengue with that of the coronavirus.