Hyderabad: Dengue appears to be following a noticeably different pattern in Telangana this year. Doctors have been observing relatively fewer cases so far and the seasonal rise is beginning only towards the end of July.

The pattern is still forming

Doctors, however, caution against drawing conclusions too early.

The dengue season generally extends into the post-monsoon period, and a clearer picture is likely to emerge only by October-November. The current pattern could be the result of several interacting factors rather than one single cause.

“Dengue data and statistics can differ from state to state depending on the surveillance and reporting system. A comparison should therefore look beyond the reported case numbers,” doctors and public-health experts said.

What happened after 2019?

The experience of previous years offers an interesting comparison.

The year 2019 was a particularly bad dengue year, with private hospitals in Hyderabad witnessing a major surge in patients, with some even putting up ‘no vacancy’ notices.

In 2020, dengue cases were comparatively low, coinciding with the Covid-19 pandemic. Reduced travel, restricted movement and changes in healthcare-seeking behaviour may have influenced transmission and reporting, although the exact contribution of each factor requires further study.

Is it because of rains?

Last year too, heavy rains began relatively early, but the number of dengue cases did not increase proportionately.

At the same time, doctors continued to encounter severe dengue cases. This suggests that rainfall alone cannot explain either the number of infections or the severity of the disease.

Changes in Aedes mosquito’s life cycle

One question that deserves closer scientific examination concerns the mosquito’s life cycle.

Aedes aegypti eggs can withstand dry conditions for prolonged periods and hatch when water becomes available. There is also evidence of vertical transmission, in which dengue virus can pass from infected female mosquitoes to some offspring. However, it would be incorrect to assume that dengue virus simply remains infectious inside all dry eggs for years. The extent to which this mechanism contributes to local transmission needs further research.

Another critical factor is the dengue serotype circulating in a particular locality.

There are four dengue serotypes — DENV-1, DENV-2, DENV-3 and DENV-4. A previous infection provides long-term immunity against that serotype, while a subsequent infection with a different serotype can carry a greater risk of severe dengue.

Therefore, two areas with similar mosquito populations can experience very different patterns of disease depending on the circulating serotype and the immunity profile of their populations.

Factors affecting dengue spread

Doctors say that the number of adult Aedes mosquitoes is only one part of the picture.

What matters is the combination of mosquito density, the proportion of infected mosquitoes, circulating serotype, population immunity, rainfall and temperature, human movement, surveillance and clinical patterns.

This makes the coming months important for Telangana.

Once the 2026 dengue season tapers off, experts should ideally undertake a comparative analysis of data from 2019 onwards, examining rainfall, mosquito indices, serotypes, geographical distribution, hospitalisations, severe cases and deaths alongside reported infections.

Such analysis will become even more important as dengue vaccines enter wider use. Strong baseline surveillance and transparent case data will be essential to assess vaccine effectiveness and safety scientifically and to identify genuine changes in disease patterns.

Need for better collection of data

Doctors stress that dengue surveillance should therefore not stop at simply counting cases. Transparent, consistent and detailed data is needed to understand why dengue rises, why some seasons are severe, and why certain infections progress to severe disease.

For now, the relatively low number of cases and severe infections in Telangana is encouraging.

But the final assessment of the 2026 dengue season should wait until the season has passed, and the data can tell us not just how many people were infected, but why the disease behaved differently this year.