It seems that COVID-19 is often spread by persons displaying no symptoms, making it particularly difficult for people to avoid spreading it. What is the best source for this? Could or should this fact to also in the CDC guidance summary list of key facts about the disease? Or has the CDC not spoken on this? Pat Palmer (talk) 20:50, 13 January 2021 (UTC)
There's an excellent editorial in the BMJ on this by Allyson M Pollock and James Lancaster (2020) https://www.bmj.com/content/371/bmj.m4851 Asymptomatic transmission of covid-19. BMJ 2020;371:m4851 Key points:
1) "Earlier estimates that 80% of infections are asymptomatic were too high and have since been revised down to between 17% and 20% of people with infections"
2) It’s unclear to what extent people with no symptoms transmit SARS-CoV-2.
3) Viral culture studies suggest that people with SARS-CoV-2 can become infectious one to two days before the onset of symptoms and continue to be infectious up to seven days thereafter.
4) Symptomatic and presymptomatic transmission have a greater role in the spread of SARS-CoV-2 than truly asymptomatic transmission
- However - "asymptomatic and presymptomatic people may have more contacts than symptomatic people (who are isolating), underlining the importance of hand washing and social distancing measures for everyone"
Public Health England today reported that "Past COVID-19 infection provides some immunity but people may still carry and transmit virus" ("Between 18 June and 24 November, scientists detected 44 potential reinfections (2 ‘probable’ and 42 ‘possible’ reinfections) out of 6,614 participants who had tested positive for antibodies. This represents an 83% rate of protection from reinfection.") The bottom line is that infection provides a high degree of immunity for at least 5 months after infection.
The study is ongoing, and the press release warned that while high levels of antibodies in those with covid give some protection from becoming ill with COVID-19, some of these individuals (with antibodies) carry high levels of virus and could continue to transmit the virus to others.