New Delhi: A study conducted in Brazil has found that the states where a large number of people contracted dengue in 2019-2020 have witnessed fewer Covid-19 cases and deaths. According to the researchers, this finding suggests that dengue antibodies may lend some level of immunity against the novel coronavirus.
Going by infection numbers, Brazil is the third worst-affected country by the Covid pandemic, having recorded 45,60,083 cases as of Tuesday. However, it has the second-highest number of coronavirus fatalities — 1.37 lakh, second only to the US’.
The study was conducted by researchers from the University of São Paulo in Brazil and Duke University, US. It is yet to be peer-reviewed and was posted on preprint portal medRxiv last week.
If proved conclusively, the study holds deep significance for India, which battles dengue outbreaks every year, and dozens of other countries where it is endemic — the disease is endemic in at least 100 countries, according to the World Health Organization.
The study sought to look at the various factors in Brazil that influenced the spread of SARS-CoV-2 or the novel coronavirus in the country. The researchers used mathematical modelling to understand the factors driving the uneven spread of Covid-19 in Brazil.
They found that, during the first three months of the pandemic, about 17 ‘super-spreading’ cities accounted for upto 99 per cent of the Covid-19 cases in Brazil.
Their modelling also reportedly revealed that “states in which a large fraction of the population had contracted dengue fever in 2019-2020 reported lower Covid-19 cases and deaths”.
It also took longer for such states to reach exponential community transmission, due to slower SARS-CoV-2 infection growth rates, the team wrote in the study.
Overall, the team found that areas that had a higher percentage of people with dengue antibodies also had lower Covid-19 incidence, infection growth rate, and mortality rates.
Based on these findings, they hypothesised that dengue antibodies may confer some level of immunity to the novel coronavirus. They also suggest that the dengue virus vaccine — there is just one licensed vaccine right now, approved in 20 countries — may help protect against Covid-19.
Not first study to link dengue-Covid
This is not the first time scientists are suggesting that dengue antibodies can confer some protection against Covid-19.
In June, a team from CSIR’s Indian Institute of Chemical Biology, led by Subhajit Biswas, became the first to suggest that dengue antibodies can bind with SARS-CoV-2.
They first conducted a computational study that suggested dengue antibodies can interrupt a process that is crucial for SARS-CoV-2 to enter human cells.
In another study posted the next month on medRxiv, they claimed that blood serum samples that had dengue antibodies can sometimes give a false positive when tested for SARS-CoV-2 antibodies. This finding sought to emphasise that serosurveillance exercises — meant to detect a population’s exposure to an infection by looking for a particular set of antibodies, in this case, Covid’s — should be accompanied with other forms of testing for more accurate results in areas where both “viruses are co-endemic”.
Both the papers, which are yet to be peer-reviewed, suggested that dengue antibodies can cross-react with protein from SARS-CoV-2 to interrupt infection.
They also suggested that a dengue vaccine may confer some level of immunity against SARS-CoV-2 infection, until a better alternative comes along.
Following up on their work, a team from Israel conducted a similar study, and was able to show that Covid-19 patients can test positive for dengue antibodies and vice-versa. The study was published last month in the peer-reviewed Clinical Infectious Diseases.
Talking about the Brazil study, virologist Shahid Jameel, who serves as CEO of the charity Wellcome Trust/DBT India Alliance and wasn’t involved in the research, told ThePrint that while the observations pointed out are interesting, more work is needed.
For example, a structure-based model comparing the two viruses needs to be seen to support the hypothesis, but this was not presented by the researchers, he said.