March 17, 2020: Doremalen et al, NEJM (experimental) showed SARS-CoV-2 remains viable in aerosols for hours, supporting airborne spread.
March 19, 2020: Zou et al, NEJM (virology observational) showed that SARS-CoV-2 reaches extremely high viral loads in the nose and throat at or before symptom onset which explained the ease of presymptomatic transmission and why COVID-19 spreads so efficiently through shared air.
March 26, 2020: Bourouiba et al, JAMA (mechanistic) highlighted that SARS-CoV-2 can spread much farther than current social distancing guidelines suggest (far past the social distance recommendation of 6 ft, up to ~23-27 ft), especially indoors
April 2, 2020: Lu et al., Emerging Infectious Diseases (outbreak investigation) found COVID-19 spread between diners seated ~1 m apart only along AC airflow, inconsistent with simple droplet spread alone. Evidence that airflow-borne respiratory particles drive indoor transmission
April 10, 2020: Lidia Morawska and Junji Cao Environment International (commentary) warned that COVID-19 spreads through the air, arguing that aerosols can travel meters indoors and urging ventilation and masking.
May 14, 2020: Sia et al., Nature (animal model / hamster study) showed SARS-CoV-2 spreads efficiently between hamsters through the air, becoming key evidence that inhaling a relatively small airborne dose over a short time can be enough to establish infection
May 15, 2020: Hamner et al., MMWR (CDC outbreak investigation) reported the Skagit Valley choir superspreading event, where one symptomatic singer infected ~87% of attendees in ~2.5 hours. The authors note singing increases aerosol emission, making droplet-only spread unlikely
May 27, 2020: Morawska et al. / Group 36, Environment International (expert correspondence): A group of 36 international aerosol, indoor-air, HVAC, and infectious-disease experts warned that airborne transmission of SARS-CoV-2 indoors was being downplayed, and called for ventilation, filtration, reduced air recirculation, and other clean-air engineering controls to limit spread
June 11, 2020: Zhang et al., PNAS (epidemiological analysis): Analyzed outbreak trends in Wuhan, Italy, and NYC and argued that airborne transmission was the dominant driver of COVID-19 spread and wearing masks as the most effective way of preventing spread
....and so on.
We knew. It was also suggested by the WHO in the infamous ‘military word: airborne’ press conference, 11 Feb 2020, and was explicitly acknowledged as a possibility in the WHO briefing on July 7 2020.
March 17, 2020: Doremalen et al, NEJM (experimental) showed SARS-CoV-2 remains viable in aerosols for hours, supporting airborne spread.
March 19, 2020: Zou et al, NEJM (virology observational) showed that SARS-CoV-2 reaches extremely high viral loads in the nose and throat at or before symptom onset which explained the ease of presymptomatic transmission and why COVID-19 spreads so efficiently through shared air.
March 26, 2020: Bourouiba et al, JAMA (mechanistic) highlighted that SARS-CoV-2 can spread much farther than current social distancing guidelines suggest (far past the social distance recommendation of 6 ft, up to ~23-27 ft), especially indoors
April 2, 2020: Lu et al., Emerging Infectious Diseases (outbreak investigation) found COVID-19 spread between diners seated ~1 m apart only along AC airflow, inconsistent with simple droplet spread alone. Evidence that airflow-borne respiratory particles drive indoor transmission
April 10, 2020: Lidia Morawska and Junji Cao Environment International (commentary) warned that COVID-19 spreads through the air, arguing that aerosols can travel meters indoors and urging ventilation and masking.
May 14, 2020: Sia et al., Nature (animal model / hamster study) showed SARS-CoV-2 spreads efficiently between hamsters through the air, becoming key evidence that inhaling a relatively small airborne dose over a short time can be enough to establish infection
May 15, 2020: Hamner et al., MMWR (CDC outbreak investigation) reported the Skagit Valley choir superspreading event, where one symptomatic singer infected ~87% of attendees in ~2.5 hours. The authors note singing increases aerosol emission, making droplet-only spread unlikely
May 27, 2020: Morawska et al. / Group 36, Environment International (expert correspondence): A group of 36 international aerosol, indoor-air, HVAC, and infectious-disease experts warned that airborne transmission of SARS-CoV-2 indoors was being downplayed, and called for ventilation, filtration, reduced air recirculation, and other clean-air engineering controls to limit spread
June 11, 2020: Zhang et al., PNAS (epidemiological analysis): Analyzed outbreak trends in Wuhan, Italy, and NYC and argued that airborne transmission was the dominant driver of COVID-19 spread and wearing masks as the most effective way of preventing spread
....and so on.
We knew. It was also suggested by the WHO in the infamous ‘military word: airborne’ press conference, 11 Feb 2020, and was explicitly acknowledged as a possibility in the WHO briefing on July 7 2020.