This post started out examining the research suggesting approximately 50% of the population were already naturally immune to Covid-19 from the outset. I review this research in this post, as well as what I think is the even more significant question: how could Covid-19 spread as it has, if 50% of people were already immune? How, and what are the implications for vaccines?
- The Research: pre-existing immunity
- Covid-19: Can It Spread Despite Immunity?
- Vaccines: The possible Outcomes
- Conclusion: Managing Outcomes.
The Research: pre-existing immunity
Independently, several research facilities are examining the same principle: Can previous exposure to the common cold provide immunity to Covid-19. The research is not yet conclusive. There are implications if this is proven to be correct, which are explored here, also the implication that for the idea to even be considered, it has to be possible that the current global outbreak of Covid-19 has occurred even despite significant levels of immunity already being present.
The further implications of the proposition is found true are:
- as almost all adults have had a cold at some time, either a significant percentage have avoided the relevant cold viruses, or the immunity does not last
- people may be immune to Covid-19 temporarily
- infection with a form of the common cold could act as a vaccine
Covid-19: Spread despite immunity?
The ability of a virus to be spread by ‘asymptomatic’ people is unusual, but it is quite well established that ‘asymptomatic’ people can spread Covid-19.
For most viruses, if you are asymptomatic, then you are not considered to have the disease the results from the virus. If you never become infections, and have no symptoms, do you actually have a disease? Even people who are fully immune can still have some infected cells. For any viral infection, there is a required threshold before the infection level is considered a ‘case’ of the disease.
A patient is immune because their system is able to kill infected cells, effectively stopping the virus from multiplying. However, even in an immune person, there is some level of spread prior to infected cells being detected and killed. The normal definition of effective immunity is that the infection never gets to the level where the patient will have symptoms.
But with Covid-19, unusually, people can be infections prior to, or without ever, reaching the level of infection where they have symptoms.
Therefore is entirely possible for a person to have immunity such they are protected from ever developing symptoms, yet still carry some virus for a time and during that time infect others.
Vaccines: The possible Outcomes.
It seems highly likely that a vaccine should be possible for Covid-19, with the main potential problems being:
- vaccines provide only a brief periods of immunity, and thus require regular ‘topups’
- Covid-19 proves able to mutate, requiring a constant update of vaccines as with influenza virus, or the common cold.
But now, there is another two possible outcomes for even a successful vaccine. This possibility for immune people to participate in spread means that search for a vaccine includes these possible outcomes:
- a vaccine is found that keeps the immune system on such high alert level that infected cell numbers never reach a level where ‘shedding’ of infected cells occurs (is this possible, or even healthy?)
- a vaccine is found that results in any infection being being contained at levels below those required to result in any symptoms, but does not prevent people infecting others
Normally, the existence of a large number of vaccinated people prevents a virus from spreading as vaccinated people do not reach the contagious stage, but with Covid-19, the virus could keep spreading. Forever, reinfecting everyone as soon as their immunity ends, and potentially wreaking havoc an anyone not able or not prepared to be vaccinated.
Any potentially, continuing to exist in sufficient numbers to continue to evolve.
Conclusion: Managing Outcomes.
The more we learn about Covid-19, the more the risks of any stragety other than elimination become apparent.
Suppression/Containment: Which is effectively trying to live with the virus until a vaccine is found, clearly has risks.
Pursuing a ‘Herd Immunity Strategy‘ has not yet proved to be a viable solution.
Taiwan effectively prevented Covid-19 from ever reaching outbreak levels, and it appears there has been no community spread for several months. I say ‘appears’ because statistics separating cases contracted elsewhere (and detected while in quarantine or on arrival) from local cases are still hard to find.
New Zealand eliminated local transmission and now exists in pre-covid conditions other than closed borders. Iceland just touched elimination, but perhaps dropped its guard too early.
Most countries remove restrictions before reaching elimination, despite the long term economic and health costs because they cannot wait until it is safe to reopen – or because the policy is the ‘containment/suppression.
The only proven strategy so for is elimination.
