INFECTIOUS PERIOD, RE-INFECTION, ANTIBODIES
I don't believe you can infect someone that you never came into contact with. Is there evidence that laboratory animals can be infected if they are placed in a cage in which previously infected animals have resided and for how long after that?
That type of experiment has not yet been done as far as I know… There is a clear evolution in thinking about transmission paths.
- Infection through objects (fomites) is probably very rare. The experiments that suggested this pathway used doses that are likely to be rare in reality (see Ref 1)
- On the other hand, contamination via aerosols has gained evidence, as they can indeed “linger” for a long time in an open space (Ref 2-4)….
With regard to very weak patients, severely handicapped, who contract Covid19, and end up in our "hospital" in our institution: when can we be absolutely sure that they can no longer cause infection? From what moment can we transfer them back into the living group with negative residents? 14 days minimum, subject to conditions, but I read in the literature for up to 6 weeks. Is this still the case? Can we test this objectively?
In Ref 5 you will find an overview of available evidence. I am copying the main conclusion here:
“There was substantial variation in the estimates, and how infectious period was inferred.
One study provided approximate median infectious period for asymptomatic cases of 6.5–9.5 days.
Median presymptomatic infectious period across studies varied over <1–4 days.
Estimated mean time from symptom onset to two negative RT-PCR tests was 13.4 days (95% CI 10.9 to 15.8) but was shorter when studies included children or less severe cases”
Conclusion: 14 days is indeed more of an average and an extra week would certainly provide additional security… ..
The following comment from another colleague illustrates the variability.
You see people who still have a high viral load a month after the first positive test.
Indeed, in the article by Gidari et al (Ref 6), you can clearly see that “recurrence” is not uncommon. It’s occurrence is certainly not limited to the elderly (mean age 47 years), the evolution was usually favorable and in vitro cultures remained negative, so probably the virus was not very infectious.
In the ideal world we would therefore first perform one (or even better two) PCR tests before declaring someone “no longer infectious” and then following up properly….
A very interesting study by Nussenzweid's group (Ref 7) was recently published, which shows that even after the negativation of the PCR, the antibodies evolve further qualitatively (even if they decrease quantitatively): they become more powerful 6 months after infection and can neutralize mutants of the receptor binding domain (RBD) on the spike. That seems a strange phenomenon, of course, if the virus has disappeared. Intestinal biopsies were therefore taken from 14 asymptomatic subjects, with a recent COVID infection, but with negative naso-pharyngeal swabs: in 7/14 the virus was detected in the intestinal mucosa by PCR and electron microscopy!
You will find some more case reports on persistent or recurrent infection in cancer patients (Ref 8-9).
To be sure of a new infection, therefore, you must ascertain that it is not a late recurrence, i.e. you should demonstrate that it is not the same virus by genetic analysis. This has not always been done, for practical reasons (see Ref 10-12), but in Ref 13-15 there is indeed genetic evidence of a re-infection.
What do antibodies in blood mean? Protection against reinfections?
As just explained, we can use COVID antibodies after natural infection as a diagnostic tool (the certified ELISAs have a high specificity and sensitivity), but it is unclear how strong their protective effect is. A number of re-infections have now been described in people who still had circulating “neutralizing antibodies” (See Ref 13-15). Along the way we will learn what titer or breath of antibodies that recognize the receptor binding domain (RBD) and / or display neutralizing activity in vitro is needed for protection.
For your information: we also have a case with positive AB in first wave, but neg PCR, now positive PCR, so mutant?
That is of course the second factor: how fast does the virus evolve in the population to escape the antibodies that are already present in (part of) the people? There are data that the virus evolves indeed by point mutations, also in the receptor binding domain (RBD) of the spike protein, see e.g. the study by Ghorbani (Ref 16 J Phys Chem Nov 2020). The authors show that the naturally occurring RBD variants maintain their binding affinity for the ACE2 receptor. We are not sure that these mutants originate as "escape" to antibody pressure, but that is very likely. In a study by Baum (Ref 17 Science Aug 2020) it is demonstrated that the RBD can indeed very easily escape by mutation from individual neutralizing monoclonal antibodies (nmAb) and even from Ab combinations targeting sites that are close to each other. Conversely, combinations of two very different nmAbs, one targeting the RBD and the second targeting a different site of the spike protein, are still able to neutralize the virus.
With genetic engineering, we can change coli bacilli to produce human insulin. Can't we try to produce antibodies against Covid-19 in this way?
Genetic techniques are indeed being used to develop powerful neutralizing mAb. An example can be found in Rogers (Ref 18 bioRxiv 15 May 2020).
A question about contact tracing. If my cell phone was in contact with a cell phone of which the owner was contagious, for more than 15 minutes at less than 1.5 meters, I have to quarantine for 10 days. This is so for Boris Johnson even though he was already infected and had been quarantined for a long enough time. How can I continue to work as a GP.
Yes, that's a good question… ..
In the vaccine that we are used to, particles of the protein capsule are injected to generate antibodies. How does an RNA or DNA vaccine work?
Why does the Pfizer vaccine have to be stored at minus 70 Celsius and at another company 7 to 8 C?
Please clarify covid vaccines based on attenuated virus (in china!
Which vaccine is in theory (from previous vaccination programs) most likely to be most effective? Or are there too many factors that have to be taken into account to answer this?
A nice overview of the vaccines in development can be found at Krammer (Ref 19 Nature 22 Oct 2020).
The DNA vaccine consists of a circular DNA (plasmid) in which the genetic code for the spike protein (or for the receptor binding domain) is integrated, together with, for example, viral promoters to enhance expression in human cells. Such a plasmid is very stable and does not even need to be stored at 4 ° C. As such, it is injected intramuscularly and some DNA will be taken up “by chance” by an “antigen-presenting cell”. It will be converted via normal cellular mechanisms into messenger RNA (mRNA) and translated into the spike protein, which will then be processed into peptides, that stimulate specific T cells and also B cells, resulting in the vaccination effect.
The fundamental disadvantage of a plasmid DNA vaccine is a very small intrinsic risk that it will mis-insert into human DNA and cause cancer. This has never been seen with vaccination, but it has been seen with certain gene therapies, where much higher and repetitive doses are used.
To obtain an mRNA vaccine, the plasmid DNA is first transcribed in vitro into the mRNA, which is then used as a vaccine. The advantage is that mRNA cannot integrate into human DNA and is therefore (even) safer than plasmid DNA. The disadvantage is that RNA is easily broken down in biological fluids, because RNAses (enzymes that destroy RNA) are active (as part of antiviral defense). Therefore, it must be formulated in a “lipo-nanoparticle”. In addition, it must also be frozen, usually at -20 ° C, but it can also be stored at 4 ° C for a short time. Why the Pfizer COVID vaccine has a requirement of -70 ° C, I don't know yet….
In the past, live attenuated vaccines of human pathogenic viruses have been obtained by propagating these viruses under "artificial" conditions, e.g. in cell cultures, on chicken embryos or in experimental animals, which are not the natural host. Thus, by chance, mutations and often deletions of whole genes arose, which made the virus non-pathogenic; while the crucial envelope or spike proteins remained immunogenic. Classic examples are the Yellow Fever vaccine and the live oral polio vaccine. While the Yellow Fever vaccine remains a very good and safe vaccine (which is now also used as a basis for a recombinant COVID vaccine in Johan Neyts' lab), there have been repeated problems of “reversion” with the polio vaccine in the past, so that now only the inactivated polio vaccine is being used.
It is therefore clearly NOT the intention to use this “old-fashioned” trial and error technique to obtain an attenuated COVID vaccine, but a more rational approach will be developed, based on the knowledge of which genes are responsible for pathology. These genes would then be selectively deleted or mutated, leaving a non-pathogen replication-competent and immunogenic variant. The principles are explained by Zhiqian Ma (Ref 20 Adv Viral Res). It is true that it is being worked on in China and India, but this is not an easy pathway and I suspect that this will not result in an applicable vaccine during the first few years anyway.
Based on previous vaccine developments, I guess that a recombinant Spike protein vaccine could be very safe and efficient. See the hepatitis B and Papilloma vaccines. But the trials with Spike proteins seem to be lagging behind the mRNA and viral vector vaccines. Both of the latter principles seem to be getting along well. They will likely prove safe and effective, but we still have to wait for scientific publications and approval by FRA and EMA. If those vaccines are available and I get to choose, I will prefer the mRNA vaccines, because I know from my own experience with experimental HIV vaccines and from a very extensive literature on anti- cancer vaccines that mRNA is safe. So this morning I was happy to hear that these vaccines will probably be the first to be approved by Europe… ..
Less response in the elderly to a vaccination?
How are the long-term effects of the corona vaccines estimated?
You have not seen any phase III studies yet, so I don't know if you can answer this, but are the vaccines also checked that they do not increase the severity of the disease?
Probably the vaccines will indeed be less effective in the elderly (see Ref 21). As far as we read in the media (but not in formal scientific publications), some of the phase 3 trials also involved 65+ people, but these are probably “healthy seniors”, who are not representative of the most vulnerable “frail” group….
It is of course too early to assess long-term effects of vaccination. Researchers are well aware of the potential risk of worsening infection after vaccination through mechanisms such as “antibody-dependent enhancement”, as this has also occurred with experimental SARS-CoV-1 vaccines. But so far there is very little evidence that such effects will occur in case of SARS-CoV-2 (Ref 22 Nat Microbiol).
Can the influence of age and comorbidity on the severity of the course of covid also be applied to other viruses?
Yes, the same goes for e.g. influenza, “normal coronaviruses” etc.
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To what extent does vitamin D play a role in covid?
There is a lot of literature on this topic. A meta-analysis of this literature was recently performed by Pereira in Crit Rev Food Science Nutrition (Ref 23). Vitamin D deficiency does not increase the risk of infection, but it does lead to more serious illness and death.
I also found 3 clinical studies on VIT D supplementation with positive effects:
- A small randomized placebo-controlled trial in India with 40 relatively young and mildly symptomatic patients (Ref 24 Astogi Postgrad Med J). There were only two significant effects after 7 days of high dose cholecalciferol (60,000 U): a greater decrease in fibrinogen (but not other inflammatory parameters) and a greater percentage of viral load negativation (but the mean time to negativation was similar in both groups). The way in which the patients were matched is also not very clear. So not very convincing results.
- A slightly larger Spanish study with 76 slightly older patients with COVID pneumonia (Ref 25 Castillo J Sterod Biochem Mol Biol). High dose calcifediol was associated with a lower chance of entering ICU (only 1 in 50, while 13/26 in the untreated group entered ICU). All Vit D supplemented patients survived, while 2 died in the control group. There was a problem of matching: clearly more Pt in the control group had prior diabetes or high blood pressure, but this was corrected for in the statistical analysis (?). The authors rightly conclude that larger studies with better matched patient groups are needed.
- Finally, a French study with 77 frail hospitalzed geriatric patients (mean age 88 years), in which 3 basically comparable groups were distinguished. Group 1 (regular chronic Vit D supplementation before the COVID episode) had the best 14 day survival (93%); group 2 with acute supplementation on admission had a survival of 81% and group 3 without Vit D only 69%. A very relative success and only significant for patients who already received Vit D beforehand.
Conclusion: there are good basic reasons for proposing vitamin D as a supplement in patients with a Vit D deficiency. But it is clearly preferable to start supplementation beforehand and the clinical evidence that it actually helps is not very strong for the time being.
14 Sept 2023 Episode 349 Update on BA.2.86 and other variants in view of the upcoming XBB.1.5 booster
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20 July 2023 Episode 340 Asymptomatic SARS-CoV-2, long COVID and vaccination revisited: genetics and evidence for “Long Vax”?
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