Mortality Patterns With COVID19

The New England Journal of Medicine has just published its first report on a series of COVID19 patients in ICU care, treated in Seattle. Although it was a small series of 24 patients, there are some instructive & sobering facts.

Firstly, cough and SOB are the danger signs, being the presenting features in almost 90% each. Fever was present in only 50%. Could it be that these slightly elderly (mean age 64) with underlying co-morbidities (58% had diabetes, 21% had CKD), are unable to mount a pyrogenic response?

Secondly, the outcome was dire. Fifty percent died, 3 (12.5%) are still ventilated and may well die, only 5/24 were discharged home and 4/24 are in hospital, but off ventilation.

What's killing them? All patients had hypoxaemic respiratory failure, but 17/24 had shock. There was no evidence of cardiac failure on Echo, so this is septic shock, requiring vasopressors.

Hypoxia and shock are a deadly combination and mostly seen in bacterial infections such as Pneumococcus, Staph or with Gram negatives, but microbiological studies showed no superinfection in these patients, either with bacteria or common respiratory viruses. it's fair to assume therefore that the cause of shock was COVID 19 itself.

You'd think this is unusual for a viral infection and you'd be right. However, it is well documented with 3 viruses. The first is a strain of Influenza A- H3N2, which is in fact a component of the trivalent or quadrivalent Influenza vaccine. In years when H3N2 circulates, the mortality rate is 2.7 times the other strains included in the vaccine.

The second is avian influenza A- H5N1, which has a case fatality rate of 60%. The third is another avian Influenza A strain- H7N9- which has a fatality rate of 27%.

The reason these other viruses haven't run amok is because they cause mainly sporadic infections, presumably due to low infectivity, and are therefore easily isolated. Unfortunately COVID19 appears to share their capacity to cause hypoxaemia and shock, while spreading much more rapidly.

Looking Back At History- Jenner's Small Pox Vaccine

How do you survive the vicissitudes of a pandemic as a doctor? Hemmed in from all sides- your patients at risk, the element of personal danger, the mortifying thought that you might pass it on to your family...things can get overwhelming.

Study helps. Updating your knowledge to keep up with the latest development is reassuring, and at least offers a semblance of control to circumstances that are largely outwith your training. However, information can sometimes overwhelm you. There's too much of it. Sorting the wheat from chaff is difficult and social media does not help.

At times like these- looking back through the ages, scouring the pages of Medical History, seeing how great men and women coped with pressure, excelled despite it, and made groundbreaking discoveries that saved millions of lives, offers comfort and peace. You feel part of a greater design. Perhaps the lives of us humble doctors has some purpose after all?

Here then is an article from 160 years ago, published on 1 March 1860 in the Boston Medical & Surgical Journal, later to be renamed The New England Journal of Medicine.

Particularly instructive is how Jenner observed that that milk maids were immune to Small Pox because of their exposure to Cow Pox- an observation that formed the basis of the first vaccine ever in 1770. However, it took him fully 25 years before he published his findings and there is an eerie parallel with Newton's consigning the discovery of differential Calculus to a drawer in his study for a quarter century, before Leibnitz made the same discovery and published it. It was still credited to Newton.

https://www.nejm.org/doi/pdf/10.1056/NEJM186003010620501?articleTools=true

Challenges to Developing a Vaccine for COVID19

While the COVID-19 pandemic spreads, hunt for a reliable vaccine is in full swing. This will take time, and there are significant barriers, both technological and financial.

A lot has been said on this blog already about the role of TLRs in dendritic cells (DC)- the principal antigen presenting cell. DCs can be myeloid, ie CD11c+ or plasmacytoid, which are CD11c-. Myeloid DCs produce many cytokines, while plasmacytoid DCs mainly produce Class I interferons.

The set of cytokines that are produced by the DC will determine which type of T cell response is activated- Th1 or Th2. In general, strong antigenic stimulation produces a Th1 response, while a weak stimulus to the DC produces a Th2 response. A Th1 response leads to activation of both cellular and humoral (antibody mediated) immunity, while a Th2 response will only lead to humoral immunity. Cellular immunity, driven by Th1 response is essential for controlling intracellular infections with viruses, bacteria and fungi. A Th2 response will reduce viraemia or bacteraemia, but will not fight intracellular pathogens.

Th1 responses are initiated by IL-12 produced by the myeloid DC, which then leads to the production of interferon-gamma by NK, NK-T and T-cells. On the other hand, Th2 responses are initiated by IL-4, IL-5, IL-10 and IL-13.

Now here's the important bit. Th1 and Th2 responses inhibit each other. Thus a Th2 response will curtail a Th1 response and thus prevent that development of cellular immunity. This can have dire consequences against organisms such M.tuberculosis, M.leprae and Leishmaniasis, Listeria.

Successful vaccines, for the most part, elicit a Th1 response. If they elicit a Th2 response instead, in some cases the underlying infection will worsen. This has been one of the principal barriers to developing a vaccine against RSV and SARS. Fortunately, the original SARS started in Nov 2002 and fizzled out by July next year. Any efforts to produce a vaccine against that virus also petered out at this point. I suspect though that similar (Th1 v Th2 response) issues may apply to COVID19.

Vaccines often produce short lived responses. One way of prolonging the action of vaccines is to administer it with an adjuvant. The original vaccine adjuvant was alum. Unfortunately, this wasn't particularly useful because it elicited a predominantly Th2 response. On the other hand, Complete Freund's Adjuvant (CFA), which is comprised of inactivated BCG and a mixture of inactivated TLR ligands, elicits a strong Th1 response in animals. Unfortunately, it cannot be used in human beings.

Other adjuvants such as monophosphoryl ester (MPL) are strongly immunogenic and elicit a predominantly Th1 response. For example, Glaxo has used a combination of MPL and alum (the latter used to adsorb the vaccine) for its HPV vaccine and subcomponent vaccine against Herpes simplex.

Sometimes, antigenic peptides can be too small to elicit an immune response by itself. This can be got around by attaching them to a larger protein, that is more antigenic. One such candidate was the keyhole limpet haemocyanin, a very large copper containing protein derived from the endolymph of an inedible mollusc. Unfortunately, it elicits a Th2 response.

There has been more success with the LEAPS technology for making small peptides immunogenic . LEAPS stands for Ligand Epitope Antigen Presentation System. This attaches a 13- amino acid peptide sequence called J-ICBL from beta-2 microglobulin (which is present in all HLA Class I molecules) to the small antigenic peptide, and thus elicits a predominantly Th1 response. This has been used to prepare vaccines against Mycobacteria, Herpes simplex and Plasmodium.

Particles of a certain size- around one micron- are preferentially taken up by APCs and macrophages. This has been used in vaccine production through microparticles called PLG, which carry either positive or negative charge. Positively charged PLG attaches to DNA, while negatively charged PLG attaches to proteins.

One of the newer techniques for viral vaccines is to introduce the viral sequence into the DNA of a harmless Adenovirus, which can then be injected into the blood and elicit an immune response. The two main candidate vaccines against Ebola both use Adenovirus as a vector. Thus, the Ebola virus glycoprotein is presented in a replication-incompetent chimpanzee adenovirus 3 (cAd3) or a replication-competent vesicular stomatitis virus. A successful Phase I trial of the first was published in NEJM in 2017.

At the end of the day, developing a successful vaccine takes time and money. In 2000, the average cost of developing a new vaccine was 800 million dollars. Current costs would be much higher. Pharmaceutical companies devote an enormous amount of time, diverting skilled professionals, to the production of a vaccine that might never work, or may not see approval due to perceived side effects.

The latter has been a particular driver of litigation against drug companies. For example, the cost of DPT rose from $0.11 to $11.00 from 1981 to 1986 due to costs of litigation. This deters future investment in vaccine production.

Reference.

Rosenthal KS, Zimmerman D. Vaccines: All Things Considered. Clin Vaccine Immunol. 2006 Aug; 13: 821–829.

Tocilizumab in COVID19

Tocilizumab is a humanized monoclonal antibody to IL-6 widely used in Rheumatology. Indications include RA, GCA, & Takayasu's arteritis.

There are some reports of it being useful in COVID19. This is not surprising, as there are similar reports of its use with the original SARS virus.

Presumably, in some of these cases, Tocilizumab helps turn down the cytokine storm, characterised by high levels of IL-6. It is important to mention that IL-6 plays an important role in infections, where it is instrumental in priming B cells, among its other functions.

However, IL-6 can also damage normal tissues quite quickly, which might be innocent bystanders not germane to the ongoing inflammatory process.

Viruses can increase the production of IL-6 through the aforementioned TLRs. TLR3 and TLR9 (cognate receptors for dsRNA and DNA respectively) act through an adapter protein called MyD88. The latter leads to two divergent pathways. While one pathway downstream of MyD88 proceeds to activate kinases IRAK1 & IRAK4 and subsequently through IRF 5&7, turns on the class I interferon genes in the nucleus, the other pathway proceeds down IRAK4 & IRAK2 to activate nuclear factor kappa B, and thus increases the production of cytokines such as TNF alpha and IL-6.

Normally, the interferon producing pathway dominates the inflammatory pathway, and most subjects overcome their viral infections through the viricidal effect of interferons.

For reasons not best understood though, in some subjects, the inflammatory pathway dominates, thus quickly leading to tissue damage, and sometimes, death. It is for these subjects that Tocilizumab might be useful.

In a similar vein, it is worth mentioning here that the IL-6 receptor activates JAK1 and JAK2 (also TYK2), which in turn, switches on STAT3. It is not inconceivable therefore that JAK inhibitors such as Tofacitinib, Baricitinib and Upadicitinib would be useful in patients with cytokine storm.

One curious effect of Tocilizumab is that it makes CRP virtually useless as a marker of inflammation. Subjects on Tocilizumab markedly reduce the production of CRP by liver, and ongoing inflammation may proceed with a normal CRP.

Antimalarials in COVID19

There have been quite a few reports on the efficacy of antimalarials- namely chloroquine & hydroxychloroquine in COVID-19, mostly from China. Some countries, specifically the Indian council of Medical Research have now put out recommendations, suggesting doctors likely to be exposed to COVID19 use hydroxychloroquine for prophylaxis. The basis for such recommendations is unclear. There is very little to commend use of these medications in the treatment of COVID19 except anecdotal reports, let alone for prophylaxis.

Presumably, these recommendations are based on some studies that show in vitro efficacy of hydroxychloroquine against certain viruses. however, there are no RCTs that show in vivo efficacy.

It is instructive that hydroxychloroquine is used principally for the treatment of autoimmune diseases such as SLE, Rheumatoid, sarcoid, DLE, etc. The mechanism by which it works in these conditions is thought to be by raising the pH of endosomes, including lysosomes. The latter operates in a facultatively acidic pH. Two immune processes that occur in lysosomes would be of relevance here.

Firstly, antigen presenting cells (APC) such as dendritic cells digest antigens internalized by Fc gamma receptors present on the cell surface. The latter of course are designed to bind to the Fc portion of IgG, and thus gain access to the antigen which the Fab portion of IgG has bound in turn. These antigens are digested in the acid environment of lysosomes and taken up in the groove of HLA Class I & HLA Class II molecules, to be presented by the APC to CD8+, and CD4+ T cells respectively. The former have particular relevance to killing viruses directly by cytolytic action, while the latter stimulate B cells through CD40-CD40L interaction. Hydroxycholoroquine abrogates this action, which is advantageous in conditions such as Lupus, where the Fc gamma portion of IgG binds to many autoantigens that would have been cleared from circulation in otherwise normal subjects. The latter is one of the principal drivers of Lupus.

A similar acid pH is required for partial digestion and activation of Toll like receptors (TLR). The 3 main TLRs dealing with viruses are all intracellular- TLR3, which binds ssRNA, TLR7, which binds dsRNA, and TLR9, which binds DNA. These TLRs are produced in the ER, and then chaperoned to endosomes by a protein called Unc90 3b, there to be partially digested and activated, ready to receive their cognate RNA or DNA. Again, turning down this function is particularly useful for SLE.

There is no conceivable reason why this should be useful for viral infections though. Perhaps the most important APC relating to viral infections is the plasmacytoid dendritic cell, which produces copious amounts of type I & type III interferons on antigenic stimulation. These interferons are viricidal, and therefore, turning down these functions would not be beneficial for viral infections.

There is a suggestion however, of a differential effect. Apparently, hydroxychloroquine differentially inhibits the processing of weak antigens such as auto-antigens in lupus while sparing the response to strong antigens such as viruses. Even if this were the case, it would only provide reassurance that the drug would not increase the risk of viral infections while being used in SLE. It would not connote a viricidal effect per se.

A Coronavirus Perspective

I wanted to make some quick points about Coronavirus, mainly from a medical perspective. Firstly, nature is a great leveller. Self enforced or socially enforced isolation means less flights, less travelling on roads, less consumption and reduced human activity. That leaves its mark on the planet...for the better. There is far less NO2 over Italy being picked up from space. The virus has achieved what years of climate conferences could not. If you push the dice too far, at some point, nature will find a way of redressing the balance.

Worries about economic growth, recessions etc are not misplaced. However, ever increasing growth at the cost of killing the planet is self defeating. As is often said, shrouds don't have pockets. We survived 5 or 10 years ago when we were poorer, and had a lower GDP, didn't we?

Second, a lot of hope is being laid at the door of vaccines. A vaccine won't be ready in time to stem the epidemic. Even if it is lab ready, it takes a long time to be ready for the bench. Abbreviating Phase I trials to speed a vaccine through Phases II & III will not have good consequences, as Gerald Ford found out in 1976 when he fast-tracked a vaccine to the general population after a swine flu scare. People died or fell ill with the jab while the swine-flu outbreak never materialised. Ford lost the election.

Finally, there's been quite a bit of talk about strengthening one's immune system to "prepare" for the virus. This is attractive in theory but may not have legs to stand on. Pharmacologically, there are far more ways of suppressing the immune system than stimulating it. And the latter, when implemented, is targeted towards various cancers rather than infections, for eg IL-2 many years ago for renal cancer, CTLA-4 antibodies such as ipilimumab for melanoma, PD-1 and PD-L1 checkpoint inhibitors for NSCC of lung, etc, and CAR-T for acute B-cell lymphoblastic leukaemias.

Furthermore, the premise that a strong immunity saves you from a virus itself needs to be examined carefully. While COVID-19 is more likely to kill the elderly and infirm, it has spared children, whose immune system is not fully developed before 2 years of age (that's why you use conjugate vaccine in very young children- they can't form antibodies to capsular polysaccharides, unless you tag on a protein). Furthermore, among the deceased were some young people without pre-existing illnesses- like the doctor in Wuhan who raised the alarm. These young men & women died of an hyperactive immune response, manifested as the cytokine storm, typically occurring during the second week of illness, with death occurring around 18 days after falling ill. This is the same sort of response that kills AIDS patients carrying an opportunistic infection after being started on HAART-called IRIS. It's the immune system doing the killing here, not the virus. There are case reports of COVID-19 patients being treated with JAK inhibitors, for example, to turn down the cytokine storm. For relatively young people therefore, it is by no means straightforward.

To find an explanation for this, looking at the way the immune system deals with the virus might be instructive. Acute viral infections are dealt with principally by CD8 positive cytotoxic T cells and Natural Killer cells, which directly lyse virus infected cells with perforin and granzymes, and through Type I and Type III interferons, which are released in large quantities by plasmacytoid dendritic cells. While the interferon pathway is meant to overcome viruses, it can be a double edged sword.

To illustrate, single stranded RNA from viruses stimulates Toll-like receptor 7, which then leads to switching on of an adaptor protein called MyD88. MyD88 can lead to two completely different pathways. One pathway leads through kinases caled IRAK1 & IRAK4 to turn on Interferon regulatory factors-5&7 in the nucleus, leading to production of alpha & beta interferons, which in turn stimulate several interferon inducible genes to fight the virus. The other pathway though leads through IRAK4 & IRAK2 to turn on NF kappa B, and thus produces cytokines like TNF alpha and IL-6 which lead to a lot of damage- ie necrosis of innocent bystander tissues through the cytokine storm.

My suspicion is that, in a subset of patients, COVID-19 is preferentially activating this second pathway.