Did COVID-19 or COVID-19 Vaccines Influence the Patterns of Dengue in 2021? An Exploratory Analysis of Two Observational Studies from North India.

Dengue experienced a rise in disease burden in 2021 in specific regions of India. We aimed to explore the risk factors of dengue occurrence and severity in the post-COVID-19 and post-COVID-19 vaccination era and performed an exploratory analysis involving participants from two prior observational studies conducted from February 2021 to April 2022 in a tertiary hospital in North India. Health care workers constituted the majority of the study participants. Individuals were stratified into five groups based on COVID-19 infection and timing of vaccination: COVID-No Vaccine, Vaccine-No COVID (VNC), COVID After Vaccine (CAV), Vaccine After COVID (VAC), and No Vaccine-No COVID (NVNC) groups. The occurrence of laboratory-confirmed dengue and severe forms of dengue were the main outcomes of interest. A total of 1,701 participants (1,520 vaccinated, 181 unvaccinated) were included. Of these, symptomatic dengue occurred in 133 (7.8%) and was "severe" in 42 (31.6%) cases. Individuals with a history of COVID-19 in 2020 had a 2-times-higher odds of developing symptomatic dengue (P = 0.002). The VAC group had 3.6 (P = 0.019)-, 2 (P = 0.002)-, and 1.9 (P = 0.01)-times-higher odds of developing symptomatic dengue than the NVNC, VNC, and CAV groups, respectively. The severity of dengue was not affected by COVID-19 vaccination but with marginal statistical significance, a 2-times-higher risk of severe dengue was observed with any COVID-19 of the past (P = 0.08). We conclude that COVID-19 may enhance the risk of developing symptomatic dengue. Future research should explore the predisposition of COVID-19-recovered patients toward other viral illnesses. Individuals receiving COVID-19 vaccines after recovering from COVID-19 particularly seem to be at greater risk of symptomatic dengue and need long-term watchfulness. Possible mechanisms, such as antibody-dependent enhancement or T-cell dysfunction, should be investigated in COVID-19-recovered and vaccinated individuals.