The mysterious summer wave driven by the ‘Indian’ coronavirus variant

Summer wave driven by the ‘Indian variant’ (delta) in the UK, Russia and Portugal (OWD)

Published: June 22, 2021
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On the ‘Indian variant’ summer wave and the mysteries of respiratory virus seasonality.

Since April/May 2020, when coronavirus infections temporarily vanished even in countries with almost no “interventions” (such as Sweden), it has been quite clear that transmission of the novel coronavirus is primarily determined by seasonal influences, similar to influenza viruses and other human coronaviruses (see charts below).

This assessment has later been confirmed by the stunning synchronicity of coronavirus infection rates in neighboring US and European states with entirely different “covid policies” (e.g. concerning face masks, school closures and business closures). Thus, most health authorities have dramatically overestimated the impact of their coronavirus policies (see charts below).

Interestingly, however, the new ‘Indian variant’ of the coronavirus (delta) appears to be the first major exception to this seasonal pattern (1). In the three northern hemisphere countries in which it has already established itself (and only in these!) – the UK, Portugal and Russia – infections in June have markedly increased (see chart above).

In the highly-vaccinated UK, the impact on hospitalizations appears to be limited so far, but Portugal and Russia – especially Moscow – report a significant strain on their health care systems and have already re-imposed new (partial) lockdowns (Russia has already lost 500,000 people to covid). Moreover, China and even Israel are also reporting new outbreaks driven by the Indian variant.

Respiratory virus transmission and seasonality

Is is important to note that while the seasonality of many respiratory viruses is well established (see charts below), virologists and epidemiologists still do not understand the factors driving this phenomenon, which is why their models fared so poorly during the covid pandemic.

Animal studies have shown that both temperature and relative humidity influence aerosol transmission, essentially bringing infections to a stop at high temperatures or high relative humidity (2). But this doesn’t explain respiratory virus transmission dynamics in the tropical and sub-tropical regions, which have never followed a typical seasonal pattern anyway (see charts below).

Thus, transmission dynamics in countries like Brazil have not been a valid counter-argument to well-established seasonality in moderate climate zones in the northern and southern hemispheres. The deeper issue here is that not only do we not understand the seasonality of respiratory viruses, but we do not even really understand virus transmission itself. (3)

The WHO initially emphasized the role of droplet transmission, triggering the face mask frenzy, but droplet transmission seems to be the least likely route, only relevant if people kiss each other or cough each other into the face, as droplets by definition cannot be inhaled.

The WHO also emphasized the role of fomite transmission (transmission via surfaces of objects, such as doorknobs), triggering the mass disinfection and “wash your hands” frenzy. Studies have confirmed that on some surfaces (including FFP2/N95 masks, by the way), the coronavirus may survive for several hours or even days. Nevertheless, so far no study has found fomite transmission to be a major route of real-world coronavirus infections (but it still might be).

In contrast, respiratory aerosols are likely a major route of coronavirus transmission, and they could explain the importance of indoor vs. outdoor transmission, the failure of facemasks, seasonality, and the higher transmission by adults vs. children and obese vs. lean people. (4)

In addition, infectious coronavirus has been shown to be present in feces, and fecal viral shedding may occur even after respiratory shedding already stopped. This enables transmission via the direct fecal-oral route (e.g. traces of fecal matter on food, in water, or transmitted by flies) and also via the fecal-aerosol route (when flushing the toilet).

While the direct fecal-oral route probably doesn’t play a major role in Western countries (although it was a major transmission route of the polio virus), the fecal-aerosol route has been confirmed in both SARS-1 and SARS-2 outbreaks and has been responsible for mysterious “no contact” transmission between multiple apartments connected via ventilation or sewage water systems.

Thus, public and private toilets are likely places of very high transmission risk and might in part explain off-season outbreaks. Interestingly, the only country that seriously tackles fecal-aerosol transmission has been China, which introduced the notorious “anal swab” testing technique and asks quarantined visitors to use disinfectant when flushing the toilet.

At any rate, the ‘Indian variant’ summer wave is real and highlights the importance, especially in high-risk people, of considering either experimental vaccines or early outpatient treatment.

Most recently, a series of randomized, double-blinded and placebo-controlled trials in Brazil found that proxalutamide – an anti-androgen drug, blocking male sexual hormones and thus inhibiting androgen-driven SARS-2 cell receptors – reduced hospitalization rates in male patients by 91%, while mortality in hospitalized patients (male and female) was reduced by 78%. (5)


  1. Previous influenza pandemics have shown that novel viruses often have off-season transmission advantages. Most recently, the 2009 swine flu achieved major outbreaks during the summer months of 2009, and largely faded away by November 2009. Thus, summer waves aren’t unprecedented, and do not refute general seasonality.
  2. Interestingly, the original outbreak of the ‘Indian variant’ in India, in April and May 2021, occurred precisely during the time of lowest relative humidity, and prior to the monsoon season.
  3. Because of this, we also don’t understand how respiratory viruses can displace each other on entire continents within just a few weeks, e.g. the novel coronavirus displacing influenza viruses and new coronavirus variants displacing previous coronavirus variants.
  4. SPR previously argued that the ‘Indian’ coronavirus variant may have gotten better at transmitting from younger and leaner people.
  5. The SPR early treatment protocol currently includes prescription-free cough medication bromhexine, which targets the same TMPRSS2 cell receptor used by SARS-2.


1) Seasonality of respiratory viruses

Seasonality of respiratory viruses

2) Covid-19: Seasonality in US Midwest states

Covid-19: Seasonality in US Midwest states


3) Influenza: Sasonality and dependency on latitude

Seasonality of influenza. Source: Hope-Simpson, 1992

See also

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