COVID-19
Simple and complex
Basis of virology is simple.
More infections imply
- More people with disease
- More hospitalizations
- More lockdown
- More economic damage
- More damage to society
- More people with long-covid
- More deaths
- Virus epidemics grow exponential.
- Weekly doubling imply 1000-fold after 10 weeks.
- More infections are harder to control
- Weekly doubling imply 1000-fold after 10 weeks.
- More virus variants will evolve
Herd immunity might end an epidemic when the maximum number of people has been infected or vaccinated if the virus induces lasting sterilizing immunity.
- Coronaviruses don’t induce herd immunity.
- Herd immunity through natural infection has never been a strategy against a severe pathogen.
Some aspects of SARS-2 are more complex, but these do not change the list above:
Excess mortality correlates with corona-related mortality
Virus-immune pathology
- Acute mortality due to wrong immune activation
- Escapes of early neutralization by immune system
- Late onset on immune activation
- Immune overreaction on high virus load
- Immune suppression mitigates severe disease
Who will develop long covid?
Long covid has been seen frequently in all age groups and all severities, in about 1 in 10 patients
- In contrast to acute disease, little is known about long covid.
- Long covid is probably a collection of diseases and mechanisms.
- The risk of long covid does not have a strong association with age or disease severity.
- About 5 to 15% still have serious complaints after 3 months. The number of diseased people declines over time but still about 1% might suffer more than a year.
- We do not know if it will cure spontaneously in all cases.
Acute disease is severe
- Pneumonia
- Delayed acute sepsis-like disease
- Risk factors identified
- Elderly
- Male
- Cardiovascular disease
- Diabetes
- Overweight
- Diminished cellular immune responses
- Decrease type I interferon production
- Vitamin D deficiency
- Relative high risk of death for every group
- Serious for children compared to other childhood diseases
- Serious for children compared to other childhood diseases
Long-term disease is serious
- Neurological damage (brain fog, loss of smell/taste)
- Immune dysregulation
- Damage to various organs
- Different risk factors (women, most unidentified)
- Little difference between young-old
- Possible related to immune escape virus & mild disease
Symptoms are poor indicator of infectivity
- Most virus before symptoms
- Asymptomatic people can spread the virus
- RT-PCR is most sensitive test
- Rapid antigen test is good indication of infectivity at that timepoint.
Immunity wanes
- After infection and vaccination.
- Rapid loss of sterilizing immunity
- No chance on herd immunity
- Reinfections can cause (severe) disease
- Virus never fades out - unlike influenza
- Vaccines protects against disease for 6-9 months
Seasonal variation in R0
- In moderate climate higher R0 in winter
Facemasks protect from infection
- Medical facemasks offer better protection
Virus variants might cause more severe disease
- Higher virus titers
- Later innate immune control by better escape
- Antigen-specific escape
This has impact on strategies how to control the epidemic.