COVID-19 Interest Group
Sept 7, 2020
CIG Bulletin #19
What everybody is talking about - Covid-19
by Eva Gero - Berkeley Rotary
The goal of this summary is to assist you in navigating between the recent, often scary, sometimes inconsistent, even misleading news that may needlessly cause anxiety.
The explanations, when not noted otherwise, are mine. Although based on the available facts and the scientific principles of immunology, they only reflect my understanding and should be considered as an opinion.
- Reinfection with Covid-19:
Fear, dread, and panic last week: some Covid-19 survivors feel stalked by the possibility of reinfection after widely publicized news on reinfection cases from Hong Kong, the Netherlands and Belgium.
Researchers in Hong Kong reported the first documented case of reinfection with Covid-19. A 33-year-old man who had mild symptoms during his first infection, in March, was found positive for the virus again in June. The patient was asymptomatic the second time around, which led experts to caution that news of the reinfection wasn't a reason to panic, and that this was a "textbook example of how immunity should work."
The immune memory gained during his first infection helped to mount a fast and robust immune response upon the second exposure, neutralizing the invading virus. The event may be termed as "re-exposure" or "second incidence" rather than "reinfection".
But a case of legitimate reinfection reported from Nevada may give reason for concern regarding the possibility of a lesser than needed immune protection against a second Covid-19 attack. https://poseidon01.ssrn.com/delivery.php? After a mild Covid-19 disease in March, a patient fell ill again, this time with more severe symptoms. Genomic sequencing of the viral material confirmed that two distinct infections occurred. At this point, reinfection is extremely rare; patients who undergo Covid-19 infection seem to be protected from reinfection.
2. Immune protection and memory
After 17 years, the recovered 2003 SARS patients were found to carry immune memory to the SARS-virus that caused the earlier 2003 pandemic. Swedish and Chinese immunologists independently found T-cell immunity in persons never exposed to Covid-19, indicating a working cross-reactivity between other coronaviruses and SARS-CoV-2. This gives hope that the developed immune memory will be lasting.
Protective effect of neutralizing antibody response after asymptomatic infection:
A recent publication describes the case of 3 crew members on a fishing boat who carried Covid-19 antibodies apparently resulting from an asymptomatic infection prior to the trip. All three of them thwarted the rampant Covid infection that broke out on the vessel during the 18-day trip while 103 of the 117 crew members became infected. This observation is very encouraging, being the first human evidence for protective immunity conferred by neutralizing antibodies. It also gave some indication that low viral doses that result in asymptomatic infection also confer protective immunity.
In addition, a collective dataset shows that SARS-CoV-2 elicits robust, broad and highly functional memory T cell responses, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19. https://www.cell.com/cell/fulltext/S0092-8674(20)31008-4?rss=yes
The fact that both the T and B cell response can be evoked by a low-level virus dose exposure may give hope that a functional herd immunity could be achieved by vaccination combined with the current level of asymptomatic infections.
3. Risk to children - Is it true that children do not get infected?
Not true. Children, if exposed to the Covid-19 virus, get infected just as everyone. However, their risk of getting ill or dying is very low compared to adults.
The British Medical Journal 8/27/2020 states the risk for children is "vanishingly small". Children must be protected from being infected because they have more frequent and closer contacts with others that provides a higher risk for infection. Also, severe inflammatory symptoms (possibly the result of secondary exposures) with grave consequences are occurring which seem to be rare but must not be taken lightly.
Explanation: Children's first response to the infection comes from their innate immune system that is known to give an effective protective response within minutes after the exposure. As a result, the virus is largely or fully eliminated before it could enter the bloodstream and disseminate into the body's various organs.
- Children as silent spreaders
Observation: Children carry large virus doses in their upper respiratory tracts. The infected children were shown to have a significantly higher level of virus in their airways than hospitalized adults in ICUs for COVID-19 treatment. The author's conclusion: children are dangerous transmitters and a great risk to others.
A similar study was posted this week by a Korean team; they found that the virus cleared slower from children than from adolescents and adults. They also came to the conclusion that children likely are dangerous spreaders.
But, not everyone agrees. "This doesn't necessarily mean the children were spreading the virus, experts say. The presence of the viral genetic material in swabs "need not equate with transmission” stated Calum Semple, professor in child health and outbreak medicine at the University of Liverpool.
In addition, *"sensitive molecular detection methods may detect viable, infective virus but also nonviable or fragments of RNA with no capability for transmission.”
Explanation: Disease transmission can occur only from a person who carries the live, infectious virus. Live virus is present between the infection/initial replication and the time when it is fully eliminated by the immune response. The presence of the live, infectious virus in children was not documented in these or any other papers that I read.
I theorize that the seemingly larger viral load in asymptomatic children may be due to the fact that the virus was, in fact, neutralized, even sterilized by the innate immunity of the children, shortly after the infection in the nasal cavity. While the live virus actively moves on about the body during the course of the disease, the neutralized virus accumulates inside the cells of the nasal epithelium and sheds with the cells in their due course, without presenting risk to self or others. But the fact that the virus does not cause disease in the same child seems to be a powerful proof in itself that the detected viral RNA is not associated with harm.
This is also in close agreement with the finding that adult Covid patients were found to shed PCR-positive viral RNA void of any live virus long past their clinical recovery.
- Disappearing antibody titers:
We often read about worries that the neutralizing antibody's level is declining and thus the immune memory is fading.
Fact: antibodies produced against a pathogen are partly used up during the elimination of the virus, and after the pathogen is cleared, the rest lingers around for 2-3 months, in a gradually declining amount. It is the B and T-memory cells that preserve the imprint of the pathogen and assure a fast and high avidity reaction whenever the pathogen reappears. The antibody titer around day 14-18 after the infection gives a measure of the immune memory but the decline and even a negative antibody test result does not mean the absence of the immune memory.
Recent observations seem to suggest that lesser antibody titers than originally expected may confer sufficient protective immune memory – indicating a good prospect for vaccines.