Damp areas might be another cause. Lack of sunlight, built damp,unhygienic uninhabitable places but despite this fact, many people choose to inhabit as they don't have places to live.

Damp areas might be another cause. Lack of sunlight, built damp,unhygienic uninhabitable places but despite this fact, many people choose to inhabit as they don't have places to live.

In the winter, the outdoor air is colder, and the air is dryer usually both indoors and out. For influenza, it has been elegantly shown in the lab that absolute humidity — the quantity of water vapor in the air — strongly affects flu transmission, with drier conditions being more favorable.

Factor 2 :  Populated Areas

One of the reasons might be overpopulated areas. People living in largely crowded areas may fall into despair more easily than few crowded areas because vast people result in the spread of this contagious disease.For example, Bangladesh being the one of the most populated countries( population density- 1,115.62 people per square kilometer) makes it prone to faster transmission whereas in Canada(population density- 4 per Km2), things are in a lot of control.It is all because the geographical location of the countries. People are more attracted to comfortable places where they can build a great community and better economy to support them.

Factor 3 : Natural Disasters

Recent news,a powerful cyclone named Amphan managed to wreck East India and Bangladesh which worsened the Covid-19 situation. Natural calamities may affect communities to move from one place to another. This can easily transmit the virus from one place to another.

Factor 4 : Weather and Air Pollutants

Reproductive number, the average number of individuals infected by each infectious person, is key to understanding transmission of diseases. Absent prior immunity and policy responses, this number is estimated to be in the range of 2-3 for COVID-19 across many locations, leading to rapid growth in the number of cases.

Factor 5 : Human Behavior

In the winter humans spend more time indoors with less ventilation and less personal space than outdoors in the summer. In particular, schools are a site of much infectious disease transmission. School terms have been strongly identified as periods of higher transmission for respiratory viruses including those causing chicken pox,  measles, and flu. The 2009 pandemic flu in the United States was very much decreased during the summer, and then came back rapidly in September.

Factor 6 : Immune System of the Host

It is possible that the condition of the average person’s immune system is systematically worse in winter than summer. One hypothesis has focused on melatonin which has some immune effects and is modulated by the photo-period, which varies seasonally. Another with more evidence is that vitamin D levels, which depend in part on ultraviolet light exposure (higher in summer) modulate our immune system in a positive way. The best evidence for the relevance of this hypothesis is that vitamin D supplementation reduces the incidence of acute respiratory infection, according to a meta-analysis of randomized trials.