Swine Flu virus changing seasonality, geography

Not just geography and seasonality, even the age group seems to be shifting with more and more children getting affected by the virus
Swine Flu virus changing seasonality, geography

Influenza H1N1 (Swine Flu), essentially considered a disease of winters, is reportedly changing in seasonality, geography as well as the age group it is affecting. The infection has already affected more than 23,000 people across India in 2019 itself, with Rajasthan bearing most of the brunt.

The peaks of the infection have changed, said Sanket Kulkarni, deputy director, National Centre for Disease Control (NCDC). “We found in 2017 that, much like earlier trends, there were at least two seasons for the virus. One was January-March and the second one was August-October. Earlier Jan-March season used to be what we call a ‘major peak’ and August-October would be a ‘minor peak’. Now this has reversed,” he said.

“The influenza virus has trans-equatorial transmission — that is it moves from the Northern Hemisphere to Southern Hemisphere and vice-versa. The former used to happen from January-March and the latter would cause the disease post-monsoon season in India or from August to October.”

Asked about the reason for the change in peaks, Kulkarni said, “The change in peak is definitely impacting us big. Research institutions should invest more resources into finding out the reasons of the same.”  

Experts say that, more than anything else, policymakers now have to alter strategies in view of ‘peak’ changes. Sarman Singh, AIIMS-Bhopal director and microbiogist, said the trends are pointing towards change of seasonality. “However, prominent research institutions are undertaking research in this regard. We would have to wait for more concrete conclusions,” he added.

Not only this, the geography of the virus also seems to have been affected. “Earlier, the cases used to come mostly from the western parts of India. In our 2017 research, we found out cases occurring even in the remote villages of Eastern India,” said Kulkarni, who is main author of the paperInfluenza A (H1N1) in India: Changing epidemiology and its implications, set to be published in the National Medical Journal of India

Trends over the last three years support his claims. Tripura for the first time in 2017 registered 44 cases, and in 2019 it has reported 25 cases of swine flu. Further, there were 216 cases in West Bengal in 2017 against seven cases in 2016.

“Some northeastern states such as Arunachal Pradesh and Tripura, which had never reported influenza A (H1N1) cases over the past eight years, notified cases for the first time in 2017. These observations require more research to understand the changing ecological and transmission dynamics, as well as potential changes in awareness and testing,” the authors say in the paper.

Not just geography and seasonality, even the age group affected by the virus seems to be shifting with more and more children getting affected by the virus. As far as the strain of the virus is concerned, NCDC says what Pune-based National Institute of Virology said earlier this year — there has been no change in the strain in 2018 and 2019.

The strain which caused pandemic in 2009 was the Californian strain of the virus. In 2017, it mutated to the Michigan strain. Till date no change in the strain has taken place after that mutation. Asked if the change in the strain also leads to change in severity of the infection, Kulkarni replied in negative. “This is no major shift but a minor drift only. It is more of an epidemiological change that can be attributed the severity of the disease,” he said.

However, the relatively newer strain could still lead to a higher number of cases. A large part of the population may still remain immunised only against the Californian strain and not against the Michigan strain.

The situation in India remains grim. The total number of cases till first week of April 2019 has already exceeded the total number of cases of 2018. Rajasthan is the worst hit — against a total number of 2,375 cases in 2018, it has already reported 4,952 cases till April 7 with 192 deaths.


 Cases in 2017

Cases in 2018

Cases in 2019

(Till April 7, 2019)


3619 (279)

2375 (221)



7,709 (431)

2,164 (97)

4,689 (143)


6,144 (778)

2,593 (461)



1,414 (76)

879 (53)

325 (9)

Tamil Nadu

3,315 (17)

2,812 (43)

363 (2)


3,260 (15)




2,835 (16)


3,554 (24)

Total (India)

38,811 (2270)

14,992 (1103)

23,289 (791)

Figures in parentheses indicate number of deaths. Source: NCDC

 Asked about government’s preparedness to tackle the rising number of cases, Union Minister of State (MoS) for Health Ashwini Choubey replied in Rajya Sabha on February 12, 2019: “Video conferences are held regularly with the nodal officers of the States to review their preparedness to combat H1N1 cases. Availability of drugs, hospital beds, ventilators, etc, for treatment of Seasonal Influenza A (H1N1 / Swine Flu) is constantly checked from the States and wherever required, assistance is provided. States have been asked to earmark separate wards/beds for patients of swine flu with adequate number of ventilators. Integrated Disease Surveillance Programme assisted lab network of 12 laboratories are providing lab support.”

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