Thread by @swapneilparikh

@ShamikaRavi We explored the possible effect of the monsoons on transmission SARS-CoV-2 in #TheCoronavirusBook. Influenza does activity does spike in the monsoon and post monsoon period in tropical countries. 1/

@ShamikaRavi Possible reasons: clustering of people indoors with increased social contact, high RH + precipitation and decreased solar radiation can prolong viron stability, lower vitamin D levels may play a role. 2/

@ShamikaRavi Let’s look at how influenza’s transmission changes with weather. First let’s distinguish between transmission patterns in temperate countries and tropical countries.
3/

@ShamikaRavi “Clear seasonal peaks are seen in January-March for Srinagar and in July and September for New Delhi.”

Differences in Influenza Seasonality by Latitude, Northern India
Parvaiz A. Koul, Shobha Broor, [...], and Renu B. Lal

wwwnc.cdc.gov/eid/article/20… 4/

@ShamikaRavi In southern India:

“The study proves the fact that influenza activity is more during monsoon and post-monsoon months”

ijmm.org/article.asp?is…

Dynamics of the occurrence of influenza in relation to seasonal variation in Chennai, Tamil Nadu: A 7 year study
R Kiruba et all 5/

@ShamikaRavi “Consistent seasonal variations in viral infections were observed only with RSV (March-August) and influenza A virus (peaks in June, December-January).”

Seasonal trends of viral respiratory tract infections in the tropics

F. T. CHEW at all

ncbi.nlm.nih.gov/pmc/articles/P… 6/

@ShamikaRavi ncbi.nlm.nih.gov/pmc/articles/P…

”The effect of RH on virus viability is mediated by salt concentration within droplets: at high RH, physiological concentrations are maintained and viruses are relatively stable.... 7/

@ShamikaRavi ...At intermediate RH, evaporation leads to increased salt concentrations, resulting in virus inactivation. At low RH (<50%), salts crystallize out of solution, yielding low salt concentrations and high virion stability.... 8/

@ShamikaRavi .... This suggest that improved stability of influenza viruses within aerosols at low ambient humidity and at high humidity.” 9/

@ShamikaRavi journals.plos.org/plospathogens/… 10/

@ShamikaRavi ccdd.hsph.harvard.edu/will-covid-19-… 11/

@ShamikaRavi The monsoons bring an increase in mosquito populations; malaria and dengue cases explode in the monsoon and post monsoon period. Influenza cases also increase. 12/

@ShamikaRavi The load on the healthcare apparatus drastically increases in the monsoon and post-monsoon period. The Indian healthcare system will crumble under the combined onslaught of malaria, dengue, influenza and COVID-19. 13/

@ShamikaRavi Let’s also distinguish between seasonal viruses and pandemic viruses. Part of the population has immunity to seasonal viruses but not against a new pandemic virus. Pandemic viruses are less affected by seasonal changes. 14/

@ShamikaRavi Large parts of India have reopened after intensive physical distancing just before the monsoons. Reopening is by itself associated with increased infection transmission. 15/

@ShamikaRavi Tl;dr other respiratory viruses do spike in the monsoon and post monsoon period in tropical countries. A variety of factors in the epidemiological triad between host, agent and environment are involved. Other tropical infections like malaria and dengue will also spike. 16/

@ShamikaRavi @threadreaderapp unroll please