COVID-19 is primarily transmitted by symptomatic patientsand presymptomatic individuals.·Moderate grade evidence estimates that approximately 20% of COVID-19 transmission may bedue to that from presymptomatic individuals.However, estimates range from 6.4% -47%.·Asymptomatic individuals and environmental contaminationappear to contributelessto disease transmission,with estimated proportionsof 6% and 10%, respectivelyfrom modelling studies
Wang, H; Reeder, B; Howell-Spooner, B; What proportion of disease transmission is due to asymptomatic, pre-symptomatic and symptomatic cases? 2020 May 8; Document no.: LAB040701v2 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2020. 12 p. (CEST rapid review report)
Howell-Spooner, B. What proportion of disease transmission is due to asymptomatic, pre-symptomatic and symptomatic cases? 2020 May 8; Document no.: LAB040701v2-01 ESR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2020. 25 p. (CEST evidence search report)
Low grade evidence shows IgG and IgM antibody response correlates with neutralizingantibody titerand viral clearance, which is suggestive of protective humoral immunity inCOVID-19 patients with mild to moderate symptoms.
There is no available evidence with which to estimate the durability of this protective response. However, if the immune response to SARS-CoV-2 resembles that toward SARS-CoV, this protective humoral immunity may persist for several years.
Higher IgG antibody titersand a robustresponse were noted in severe to criticallyill patients and were associated with lower viral clearance and a worse clinical prognosis.
Low grade evidence suggests that convalescent plasma treatment may improve the clinical status of critically ill COVID-19 patients(one case series with only five patients enrolled).