Some attribute it to impact of COVID-19-appropriate behaviour and others to under-reporting or seasonality
Although the second wave of COVID-19 had overwhelmed the State’s health infrastructure, there has been a pronounced decline in the number of Influenza ‘A’ H1N1 and dengue cases so far this year.
While just one H1N1 case has been reported this year in the State (from Bengaluru Urban), as many as 1,044 dengue cases have been reported from January till July 2. The number of dengue cases have reduced by half in the first quarter (903 cases from January till May) this year compared to the 1,887 cases reported in the corresponding period last year.
The State had recorded a total of 458 H1N1 cases and three deaths in 2020 when the pandemic began. While 3,685 dengue cases had been reported, there were no deaths due to this vector borne disease.
Bhanu Murthy, State Joint Director for Communicable Diseases, attributed the decline in H1N1 cases to increased surveillance and COVID-19 precautions such as use of masks and social distancing as it is also a respiratory infection. However, some doctors said there could have been under-reporting of cases because of limited hospital access during the lockdown.
Virologist V. Ravi, who formerly headed the department of Neuro Virology at NIMHANS and is now part of the State’s COVID-19 Technical Advisory Committee (TAC), attributed the marked decline in H1N1 cases to herd immunity.
“Although the first outbreak of H1N1 was reported in 2009 in India, we developed herd immunity only around 2015 as there were no vaccines available for this respiratory disease,” he said.
“The low number of cases so far does not mean that there will be fewer cases this year. The virus exhibits seasonality. But with COVID-19 appropriate behaviour, we will have to wait and watch,” he said.
State Health Director Om Prakash Patil said dengue in Karnataka has been following a pattern of spiking every alternate year. According to data, 6,083 cases and eight deaths were reported in 2016 while 17,844 cases and 10 deaths were reported in 2017 followed by 4,848 cases and four deaths in 2018.
The next year, the State saw 18,183 cases and 17 deaths followed by 3,685 cases in 2020. “As last year had witnessed a dip, this year we are expecting a rise. However, till July 2, only 1,044 dengue cases have been reported,” he said.
Sudarshan Ballal, chairman, Manipal Hospitals, and member of the State’s COVID-19 expert committee, said protocol helped in keeping away H1N1 too. Less construction activity due to the lockdown had prevented mosquito breeding, he said.
“Dengue is related to mosquito breeding in stagnant fresh water and high-density populations where infected mosquitoes can bite a large number of individuals in a cluster. It is possible that many migrant workers were displaced and severe crowding in the lower socio-economic area might have been less during the pandemic,” he said.
Raghu J., Senior Consultant (Internal Medicine and Infectious Disease Specialist) at Sakra World Hospital, said as H1N1 and COVID-19 have similar manifestations, doctors are always considering H1N1 if a patient does not respond to COVID-19 treatment.
“Dengue cases too are decreasing as people are limiting outdoor activities. Staying indoors, people are not exposed to the vector much. However, over the last month, I have seen at least five dengue and two H1N1 patients,” he added.