COVID-19
Epidemic, pandemic and can it be controlled?
- What is the difference between epidemic, pandemic and endemic?
- What is the default strategy against a virus epidemic?
- Is test, trace and isolate possible?
- Does the RT-PCR detect the virus?
- Can I pass the virus if I do not have any symptoms?
- Will vaccination stop the epidemic?
What is the difference between epidemic, pandemic and endemic?
- Epidemic is a new local outbreak (of a virus).
- Pandemic is a new outbreak worldwide (of a virus).
- Endemic is a (virus) infection disease that remains in area.
What is the default strategy against a virus epidemic?
Test, trace and isolate.
- In virus epidemics (and some bacteria) infected hosts (humans) are the main source of new contaminations.
- Test, trace and isolate aims to identify infected people early on, and avoid that these transfer the disease to other people.
- The test, trace and isolate does not need exhorbitant testing facilities like population testing.
Is test, trace and isolate possible?
Yes, it has proven efficacy against very contagious diseases that were endemic, and against SARS-2 in some Asian countries.
- It should be noted that a lockdown strategy might be needed first, to enable the test, trace and isolate strategy to be effective.
- The seasonal variation in spreading of coronaviruses will reduce virus transmission in temperate areas
Does the RT-PCR detect the virus?
Yes, because the virus RNA is not stable enough to remain after infection. However, RNA detection is very sensitive and not everyone with the virus would be infectious.
- In the test tube the reverse transcriptase enzyme will copy the mRNA molecule into DNA, which subsequently will be doubled in every Ct cycle. Because of the instability of the RNA (see 1) someone will not have virus RNA from an infection that has been completely eradicated.
- People recovering from SARS-2 might have very low virus levels and would be unlikely to infect someone else. Thus, low levels of virus in a person recovering from the virus are nothing to worry about.
- However, early in infection, someone might also have very low virus levels, which would rapidly increase in the days thereafter. In this case the RT-PCR detects the virus earlier than the antigen test, that detect virus proteins.
- The inventor of the PCR, Mullis, who died mid 2019, used RT-PCR to detect the HIV virus, the causitive agent of AIDS.
- The RT-PCR protocol is rather robust. The initial protocol was developed to detect all SARS-like viruses, but no SARS-1 or other virus infections have found. The protocol was refined with additional controls.
Can I pass the virus if I do not have any symptoms?
Yes, and most virus transmission will occur before someone has symptoms.
- Most viruses are infectious prior to causing symptoms.
- People’s behaviour often changes strongly after being ill, strongly reducing the odds of contaminating other people.
- The first information that also SARS-2 could be transmitted by infected people without symptoms dated January 2020.
- A study from July 2021 has shown that people become infectious within 2 days of infections and have the highest virus titers 3 to 1 days before the onset of symptoms.
Will vaccination stop the epidemic?
No, vaccination will protect against disease but not against infection.
- Immunity against coronaviruses and other airway viruses is rarely sterilizing.
- Sterilizing immunity is required for herd immunity to stop the epidemic.
- However population immunity, the fraction of population protected from the disease is crucial to reduce the number of infections and hospital submission in an epidemic.
