EXCLUSIVE-Brazilian research points to an inverse correlation between dengue and Covid-19 cases


Places where a large part of the population contracted dengue last year and earlier this year took longer to have exponential community transmission of Covid-19 and recorded fewer numbers of cases and deaths caused by the new coronavirus, indicating a possible immunological interaction between two viruses, according to a study led by Brazilian scientist Miguel Nicolelis.

Comparison between geographical distribution of Covid-19 cases and their incidence until June 30, 2020 and dengue cases and incidence in Brazil until May 31, 2020; and sum of all dengue cases and incidence from 2019 until May 31, 2020 UFPB / via REUTERS

Photo: Reuters

According to Nicolelis, professor at Duke University in North Carolina, who since the beginning of the pandemic has been dedicated to studying the behavior of the coronavirus in Brazil, there is even the possibility that vaccines approved or under development for dengue may cause some form of protection against the new coronavirus.

“This surprising discovery raises the intriguing possibility of a cross reaction between the dengue virus and SARS-CoV-2. If proven correct in future studies, this hypothesis may mean that dengue infection or an eventual immunization with an effective vaccine and safe for dengue could produce some type of immune protection for SARS-CoV-2, before a SARS-CoV-2 vaccine became available, “says the study, seen exclusively by Reuters, which was sent to a research repository to be published in scientific journals.

The researcher pointed out, in an exclusive interview with Reuters, that there are already studies showing that people who have positive serology for dengue test positive for coronavirus without having coronavirus, suggesting that these people produce an antibody that acts on both diseases.

“This indicates that there is an immunological interaction between the two viruses that no one would expect, because the two viruses are from completely different families,” he said.

The study points to a significant negative correlation between incidence, mortality and growth rate of Covid-19 and the percentage of the population with levels of IgM antibodies to dengue in the States of Brazil, a country that has the third largest Covid-19 outbreak in the world, with more than 4.5 million, and the second highest number of deaths caused by the disease, with almost 137 thousand.

The observation was made by Nicolelis and his team when preparing a study on the geographical spread of Covid-19 in Brazil and the role of highways as a factor for the distribution of cases. The scientist noticed voids of cases on the map in certain regions of the country with no apparent explanation, and set out in search of possible explanations.

The answer, according to Nicolelis, appeared when analyzing the geographic distribution of dengue cases in Brazil in 2019 and 2020, which occupied exactly the holes in the Covid-19 case map. The case curves of the two diseases reinforced the discovery, since the dengue outbreak began to decline sharply in the country at the same time as the new coronavirus.

“It was a shock, it was a total accident. In science it happens, you are shooting to the side and you hit the target that you never imagined you would shoot,” said the researcher about the discovery.

“I went to the Ministry of Health to see if there was any explanation for these strange things, if there were other indicators of diseases that I was not aware of, and suddenly I find the 2020 dengue map of Brazil. I took the map of coronavirus cases and I put it side by side with the dengue map, and found what we call complementary distribution: regions with little coronavirus are full of dengue. “

States like Paraná, 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, took much longer to reach a level of high community transmission in Covid- 19 than states such as Amapá, Maranhão and Pará, for example, which had few dengue records in the same period, according to the study.

While Amapá took about 60 days to reach 500 cases of Covid-19 per 100 thousand inhabitants, Paraná took more than 120 days. In comparison, Amapá has an incidence of 5.4 dengue cases per 100 thousand inhabitants this year, while Paraná has the highest incidence in the country, with 2,295.8 cases per 100 thousand.

The study considers, however, that in regions with high demographic density, there is a prevalence of Covid-19 even when there is a high incidence of dengue.

“Our epidemiological results suggest the hypothesis, which has yet to be tested widely, that SARS-CoV-2 competes with the dengue virus for the same people, for the same pool of susceptible ones. As SARS-CoV-2 is transmitted man, he would have a great advantage to win this competition, in relation to dengue, which depends on a mosquito “, said Nicolelis, remembering that the research is an epidemiological study, without any serological study.

The survey points to data from the Ministry of Health that show that dengue cases in Brazil, which started the year at a much faster pace than in 2019, had a sharp drop from the epidemiological week number 11 (ended on 13 March), at the same time that the Covid-19 cases accelerated. More than that, the dengue outbreak ended in the country weeks earlier than in the previous year, while Covid-19 was advancing.

“Still according to our hypothesis, as the coronavirus spread more quickly and infected more people, there would be fewer people left to be infected by the dengue virus, and this could explain the sudden drop in the dengue curve this year that occurred in around the world “, he said, minimizing the official position of health authorities who point to possible underreporting of dengue due to the pandemic.

To validate the observation made in Brazil, Nicolelis expanded the analysis of the correlation between dengue and coronavirus to 15 other countries in Latin America, Africa and Asia, and the behavior was repeated, according to him.

As an example, the researcher cites cities at more than 2,000 meters above sea level – where there is no dengue, since the transmitting mosquito does not reach this altitude – as places with a high incidence of Covid-19 cases.

“When the incidence of Covid-19 versus the incidence of dengue in 2019-2020 was plotted for these countries, we again obtained a significant exponential inverse correlation. In other words, the more dengue cases a country had during the global dengue epidemic in 2019 and in the first months of 2020, fewer cases of Covid-19 the country registered until July 2020. Basically, this was very similar to the results obtained using data for Brazilian states “, states the study.

As another form of control of the study, Nicolelis’s team also compared Covid-19 statistics with data on chikungunya – a disease also transmitted by the Aedes aegypty mosquito – in Brazil, and there was no correlation, he said.

Since there is still no treatment or vaccine available for Covid-19, Nicolelis argues that his study could open the door to a possible way to fight the pandemic.

“Obviously this is a preliminary study from the point of view of what to do, but it opens a door that can be quickly explored, and if it is true, you can have a degree of protection for coronavirus if you have had dengue or if you are immunized for dengue. I can’t say what the percentage is, but it is enough to appear on these charts. Something exists, “he said.

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