Estimating the Risk of Human Herpesvirus 6 and Cytomegalovirus Transmission to Ugandan Infants from Viral Shedding in Saliva by Household Contacts

Thakkar

et al. 2021

Sci Rep

Self Cite

Masks are a vital tool for limiting SARS-CoV-2 spread in the population. Here we utilize a mathematical model to assess the impact of masking on transmission within individual transmission pairs and at the population level. Our model quantitatively links mask efficacy to reductions in viral load and subsequent transmission risk. Our results reinforce that the use of masks by both a potential transmitter and exposed person substantially reduces the probability of successful transmission, even if masks only lower exposure viral load by ~ 50%. Slight increases in mask adherence and/or efficacy above current levels would reduce the effective reproductive number (Re) substantially below 1, particularly if implemented comprehensively in potential super-spreader environments. Our model predicts that moderately efficacious masks will also lower exposure viral load tenfold among people who get infected despite masking, potentially limiting infection severity. Because peak viral load tends to occur pre-symptomatically, we also identify that antiviral therapy targeting symptomatic individuals is unlikely to impact transmission risk. Instead, antiviral therapy would only lower Re if dosed as post-exposure prophylaxis and if given to ~ 50% of newly infected people within 3 days of an exposure. These results highlight the primacy of masking relative to other biomedical interventions under consideration for limiting the extent of the COVID-19 pandemic prior to widespread implementation of a vaccine. To confirm this prediction, we used a regression model of King County, Washington data and simulated the counterfactual scenario without mask wearing to estimate that in the absence of additional interventions, mask wearing decreased Re from 1.3–1.5 to ~ 1.0 between June and September 2020.

Section: Discussionmentioning

confidence: 78%

Slight reduction in SARS-CoV-2 exposure viral load due to masking results in a significant reduction in transmission with widespread implementation

Thakkar

et al. 2021

Sci Rep

Self Cite

“…For influenza, the dose of viral exposure is related to the probability of infection in human challenge studies ( Memoli et al, 2015 ) and early antiviral treatment reduces household transmission ( Pebody et al, 2011 ; Goldstein et al, 2010 ). Household shedding of human herpesvirus-6 is closely linked to subsequent infection in newborns ( Mayer et al, 2020 ) and infants shedding high levels of cytomegalovirus in the oropharynx predictably transmit the virus back to their mothers ( Boucoiran et al, 2018 ). Studies in mice definitively demonstrated that viral exposure dose determines likelihood of SARS-CoV-1 infection, ( Watanabe et al, 2010 ) and SARS-CoV-2 experiments in golden hamsters are also highly suggestive of dose-dependent infection ( Sia et al, 2020 ).…”

Section: Introductionmentioning

confidence: 99%

Viral load and contact heterogeneity predict SARS-CoV-2 transmission and super-spreading events

Cardozo-Ojeda

et al. 2021

eLife

179

215

SARS-CoV-2 is difficult to contain because many transmissions occur during pre-symptomatic infection. Unlike influenza, most SARS-CoV-2 infected people do not transmit while a small percentage infect large numbers of people. We designed mathematical models which link observed viral loads with epidemiologic features of each virus, including distribution of transmissions attributed to each infected person and duration between symptom onset in the transmitter and secondarily infected person. We identify that people infected with SARS-CoV-2 or influenza can be highly contagious for less than one day, congruent with peak viral load. SARS-CoV-2 super-spreader events occur when an infected person is shedding at a very high viral load and has a high number of exposed contacts. The higher predisposition of SARS-CoV-2 towards super-spreading events cannot be attributed to additional weeks of shedding relative to influenza. Rather, a person infected with SARS-CoV-2 exposes more people within equivalent physical contact networks, likely due to aerosolization.

“…For influenza, the dose of viral exposure is related to the probability of infection in human challenge studies, 14 and early treatment reduces household transmission. 15 , 16 Household shedding of human herpesvirus-6 is closely linked to subsequent infection in newborns, 17 and infants shedding high levels of cytomegalovirus in the oropharynx predictably transmit the virus back to their mothers. 18 …”

Section: Introductionmentioning

confidence: 99%

Wrong person, place and time: viral load and contact network structure predict SARS-CoV-2 transmission and super-spreading events

Cardozo-Ojeda

et al. 2020

Preprint

Self Cite

SARS-CoV-2 is difficult to contain because most transmissions occur during the pre-symptomatic phase of infection. Moreover, in contrast to influenza, while most SARS-CoV-2 infected people do not transmit the virus to anybody, a small percentage secondarily infect large numbers of people. We designed mathematical models of SARS-CoV-2 and influenza which link observed viral shedding patterns with key epidemiologic features of each virus, including distributions of the number of secondary cases attributed to each infected person (individual R0) and the duration between symptom onset in the transmitter and secondarily infected person (serial interval). We identify that people with SARS-CoV-2 or influenza infections are usually contagious for fewer than two days congruent with peak viral load several days after infection, and that transmission is unlikely below a certain viral load. SARS-CoV-2 super-spreader events with over 10 secondary infections occur when an infected person is briefly shedding at a very high viral load and has a high concurrent number of exposed contacts. The higher predisposition of SARS-CoV-2 towards super-spreading events is not due to its 1-2 additional weeks of viral shedding relative to influenza. Rather, a person infected with SARS-CoV-2 exposes more people within equivalent physical contact networks than a person infected with influenza, likely due to aerosolization of virus. Our results support policies that limit crowd size in indoor spaces and provide viral load benchmarks for infection control and therapeutic interventions intended to prevent secondary transmission.