Graphical abstract

Co-endemicity of SARS-CoV-2 and dengue virus (DV) infection is becoming a matter of serious concern as it has been already reported that antibodies (Ab) elicited by SARS-CoV-2 infection can produce false-positive results in dengue IgG and IgM rapid tests and vice versa. Here we communicate that five of thirteen DV antibody-positive serum samples from Kolkata, archived in 2017 (predating the COVID-19 outbreak), produced false-positive results in SARS-CoV-2 IgG/IgM lateral flow-based rapid tests. Our results emphasize the importance of implementing tests with higher specificity to conduct sero-surveillance for accurate estimation of SARS-CoV-2/DV prevalence in regions where both viruses now co-exist.

Five of thirteen Dengue antibody- positive serum samples, dated 2017 (pre-dating the COVID-19 outbreak) produced false-positive results in SARS-CoV-2 IgG/IgM rapid strip tests. Our results emphasize the importance of NAT and/or virus antigen tests to complement sero-surveillance for definitive diagnosis of COVID-19/Dengue in regions where both viruses are co-endemic.

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We congratulate the authors of the recently published article in your journal on their efforts to raise public health concern for COVID-19 and dengue detection in countries where both now co-exist.Three cases were presented. One was described as the first report of dengue-COVID-19 co-infection based on positive results in dengue NS1 and IgM tests, dengue serotyping and detection of SARS-CoV-2 by qRT-PCR. The other two cases were diagnosed as dengue only by the same tests, but COVID-19 negative as SARS-CoV-2 qRT-PCR was negative. Sera from all three cases cross-reacted in COVID-19 rapid tests. For the first case, this was obvious as antibodies to both viruses were present.The authors concluded that the dengue sera in the last two cases gave "false-positive" results in COVID-19 tests (since they were SARS-CoV-2 negative by qRT-PCR) and explained that this "cross-reactivity" was due to antigenic similarities between these two viruses. However, we think that an alternative and equally plausible explanation could be that both these patients were silently exposed to COVID-19 beforehand, remained asymptomatic during viraemia for about three weeks or so (Zou et al., 2020) and subsequently turned SARS-CoV-2 negative on qRT-PCR testing, due to virus clearance/low abundance (Wajnberg et al., 2020). Meanwhile, they developed COVID-19 antibodies, which are detectable for several months after infection (Ibarrondo et al., 2020). In this phase, if they contracted dengue, the reactivity in COVID-19 rapid tests was not necessarily due to "cross-reacting" dengue antibodies but could also have been due to pre-existing COVID-19 antibodies (Clarke et al., 2020). This is particularly possible for samples collected in the time frame when both diseases are co-existent in the population.Our same argument holds for the two Singapore case reports (Yan et al., 2020), where in a reverse scenario, sera from COVID-19 RNA-positive patients showed reactivity in dengue rapid antibody tests despite being dengue PCR-negative. Singapore is highly endemic for dengue (Tan et al., 2019). Therefore, it cannot be ruled out that both elderly patients had contracted dengue in the past and had pre-existing dengue antibodies in their serum.Nevertheless, we concur with the authors that there do appear to be antigenic similarities between SARS-CoV-2 Spike and dengue envelope, as evident from our observation that archived dengue serum samples from 2017, pre-dating the COVID-19 pandemic, cross-reacted in COVID-19 rapid antibody tests (Biswas and Sukla, 2020;Nath et al., 2020Nath et al., , 2021 and later independently confirmed by others (Lustig et al., 2020). ContributionSB drafted the letter and critically evaluated the final version. All co-authors have contributed in collecting supporting data and references; writing of the letter and in discussions to arrive at the final version.

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The world is going through the scourge of COVID-19 pandemic since last several months. The pandemic appears to be less severe in highly Dengue endemic countries. Furthermore, COVID-19 in two elderly patients (with no evidence of Dengue virus (DV) infection) elicited antibodies that gave false-positive results in DV serological tests. We anticipated that SARS-CoV-2 and DV share antigenic similarity and performed molecular docking studies. Our computational modelling studies predicted that human anti-DV antibodies can indeed, bind to RBD of SARS-CoV-2 Spike protein. Some of these interactions can also potentially intercept human ACE2 receptor binding to RBM. Our computational analysis showed that m396 Ab (against SARS-CoV-1) did not dock with RBM of SARS-CoV-2, a fact already proven experimentally. This confirmed reliability and robustness of our approach. So, immunological memory to DV in endemic countries is thwarting COVID-19. Available Dengue vaccines can be repurposed against SARS-CoV-2 in DV non-endemic countries until approved vaccines/ antivirals become available against COVID-19. Based on the observations that COVID-19 and Dengue severity maps do not tend to overlap and the fact that serological cross-reactivity has been reported for COVID-19 antibodies with Dengue antigen (s), together with results from our computational studies, it is imperative that serology-based diagnosis should be complemented with NAT/virus antigen detection-based tests for definitive diagnosis of either disease in regions where both of these viruses are now co-existent. Furthermore, we still do not know whether antibodies to SARS-CoV-2 will hinder/ameliorate DV infections by binding to DV particles and reduce dengue incidences in the future or, augment DV infection and severity by means of antibody-dependent enhancement (ADE).

SARS-CoV-2 has emerged as pandemic all over the world since late 2019. In this study, we investigated the diversity of the virus in the context of SARS-CoV-2 spread in India. Full-length SARS-CoV-2 genome sequences of the circulating viruses from all over India were collected from GISAID, an open data repository, until 25thJuly, 2020. We have focused on the non-synonymous changes across the genome that resulted in amino acid substitutions. Analysis of the genomic signatures of the non-synonymous mutations demonstrated a strong association between the time of sample collection and the accumulation of genetic diversity. Most of these isolates from India belonged to the A2a clade (63.4%) which has overcome the selective pressure and is spreading rapidly across several continents. Interestingly a new clade I/A3i has emerged as the second-highest prevalent type among the Indian isolates, comprising 25.5% of the Indian sequences. Emergence of new mutations in the S protein was observed. Major SARS-CoV-2 clades in India have defining mutations in the RdRp. Maximum accumulation of mutations was observed in ORF1a.Other than the clade-defining mutations, few representative non-synonymous mutations were checked against the available crystal structures of the SARS-CoV-2 proteins in the DynaMut server to assess their thermodynamic stability. We have observed that SARS-CoV-2 genomes contain more uracil than any other nucleotide. Furthermore, substitution of nucleotides to uracil was highest among the non-synonymous mutations observed. The A+U content in SARS-CoV-2 genome is much higher compared to other RNA viruses, suggesting that the virus RdRp has a propensity towards uracil incorporation in the genome. This implies that thymidine analogues may have a better chance to competitively inhibit SARS-CoV-2 RNA replication than other nucleotide analogues.