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April 2022

A Single Gene Doubles Risk Of COVID Death

“Nothing shocks me. I’m a scientist.” —Indiana Jones

British scientists recently identified an allele, or a version of a gene, that portends lung failure and death in COVID-19 patients. Research recently published in the journal Nature Genetics, found that a poorly studied gene expressed in lungs, designated LZTFL1, has a variant form that does not differ in its coding sequence. That is, the different alleles of the gene express the same protein sequence. They do differ, however, in their non-coding sequences that regulate expression of the gene. When expressed, the gene product prevents cells lining airways and the lungs from responding properly to the CoV-2 virus. The lining of the lung essentially transforms into less specialized cells which affects their normal function.

Previous work had identified a stretch of DNA on human chromosome 3 that doubled the risk of death from COVID. Using an artificial intelligence algorithm to analyze millions of genetic sequences from hundreds of cell types from all parts of the body, the Oxford University Howard Hughes research team honed in on the lung-specific genetic off-on switch. This is another example of what I previously labeled "BioX," the new frontier of bioscience, or post-molecular biology science.

Importantly, the variant allele that augurs a worse lung response to infection does not affect the immune system. Therefore, the it is probable that vaccination remains the best way to protect these at-risk patients. Finding this new allele could also lead to novel therapies to target the pathway affected by this genetic variant to provide targeted treatment for at-risk populations.

The troublesome variant is mostly found in people of South Asian ancestry—some 60% of whom carry the allele—which partly explains the severe devastation from COVID seen in the Indian subcontinent. In contrast, 15% of those with European ancestry and 2% of Afro-Caribbean people carry the risky allele.

It will be interesting to see if this lung-specific gene also affects the course of other respiratory infectious diseases.

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Lingering Post-COVID Vascular Risks

George Burns once opined that “the secret of a good sermon is to have a good beginning and a good ending; and to have the two as close together as possible.” The same might be said for blogs. If so, this is a pretty good blog post.

We have known for some time that patients with COVID-19 are at risk for dangerous blood clots (also called deep vein thrombosis, or DVT), pulmonary embolism, and bleeding. Findings reported this month in the British Medical Journal reveal that this risk continues several months after COVID recovery.

The study compared more than one million people in Sweden who had COVID-19 to a control group of more than 4 million people who did not. The overall risks for each problem were low, but still elevated for up to six months following COVID. According to the report, DVT occurred in 0.04% of patients who had had COVID and in just 0.01% of control patients during the same time. Pulmonary embolism occurred in 0.17% of post-COVID patients and in 0.004% of control patients. And bleeding events occurred in 0.10% of patients who had recovered from COVID, while only 0.04% of control patients had such a problem.

While the risks of blood clots and bleeding were highest in patients whose COVID had been more severe, those who had had mild COVID still showed an elevated risk.

Bottom line: You are not out of the woods after you recover from COVID. Significant problems can arise a few months later.

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COVID-Diabetes Link Confirmed

As I penned in these virtual pages almost a year ago, COVID survivors have a high risk for developing diabetes. Early on, diabetes was identified as a risk factor for severe COVID illness, but two years later, scientists were surprised by the unforseen reverse correlation between COVID and the metabolic condition. The increased risk for diabetes in COVID survivors was recently confirmed by US and German scientists.

A study of more than 180,000 American veterans done at the St. Louis VA Health Care System found that COVID survivors were 40% more likely to get a new diagnosis of diabetes within a year of their COVID diagnosis than a control group of veterans who avoided the virus. That works out to about 13.5 extra cases of diabetes per 1,000 COVID patients.

The increased risk for diabetes was evident even in people who had a low risk of diabetes before COVID, and the likelihood of newly diagnosed diabetes increased with the level of care patients received for COVID. In other words, the sicker the patients were with COVID, the more likely they were to develop diabetes.

The other study from Germany found that people who had mild COVID cases were 28% more likely to be diagnosed with type 2 diabetes compared to a control group consisting of patients who had an upper respiratory tract infection caused by a different bug. That study was based on an analysis of electronic records from a nationwide primary care database that followed patients, including almost 36,000 COVID cases, for 3-5 months. This means that these newly diagnosed cases of diabetes arose quickly after COVID infection, and were not a result of general respiratory infection, but were a specific consequence of CoV-2 infection.

Questions remain about whether diabetes that follows COVID is just temporary and reversible after patients fully recover, or whether it leads to chronic disease. In other words, if you had even mild COVID, you should ask your doctor to screen you for diabetes, which simply entails a fasting blood draw to test for glucose and hemoglobin A1c levels, which are elevated in diabetic patients.

A lingering question is how COVID leads to diabetes. Does the virus directly affect the insulin-secreting beta cells in the islets of the pancreas, or is new-onset diabetes caused by metabolic changes in fat cells which we know are readily infected by the virus. It is also possible that insulin production is perturbed by viral damage to the cells that line vessels supplying blood to the pancreas, indirectly causing death of insulin producing cells. A more trivial cause for post-COVID diabetes could simply be an unveiling of incipient diabetes that might have gone undiagnosed because people have been away from the health-care system during the pandemic. It is also possible that steroid medications prescribed to tame the COVID inflammatory response could elevate glucose levels in the blood, leading to a diabetes diagnosis.

Research into the cause of the COVID-diabetes link continues apace—stay tuned.

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Why Don’t The COVID Vaccines Last Longer?

The FDA just authorized a second booster shot of the Pfizer-BioNTech and Moderna coronavirus vaccines for people over 50 and the CDC has approved it. A second booster has already been approved in the U.K., Sweden, Israel and Denmark.

Why do we need a second booster only months after the first booster, which came only months after most of us received two jabs of either the Pfizer-BioNTech or Moderna mRNA vaccines? Are the vaccines not very good? After all, we get small pox or measles shots that last a lifetime. Others, like the vax for tetanus, last for ~10 years. Why can’t we get a more durable coronavirus vaccine?

The answer is complicated and largely rooted in both viral biology and vaccine immunology.

Viral biology. The simplest answer is that viral mutation can change the molecules the vaccine immune response is trained to recognize, causing vax immunity to decay as viruses mutate. The coronavirus vaccines are directed against the spike protein expressed on the original CoV-2 that first appeared in Wuhan, but that ancestral bug has spawned mutated progeny that look a bit different to the immune system. In other words, viral variants created by “antigenic drift” become less recognizable to the immune system. That is why the vaccines are somewhat less effective against the Omicron variant that carries numerous point mutations in its spike protein. The current vaccines are still pretty effective against current viral variants, but continued antigenic drift along with the selection of variants that can better avoid vaccine immunity will likely require new vaccines in the future.

So, why do we need new flu vaccines every year, and need frequent CoV-2 vaccines, but we don’t similarly need new measles vaccines? Measles, mumps, flu, COVID, and other diseases are caused by viruses, but the different viruses behave quite differently. Viruses carry relatively little genetic material that tends to mutate as they replicate and spread. Some viruses, like flu, also have a “segmented genome” meaning that their genetic material is carried on several separate genetic molecules, making it easy to shuffle their genomes like a deck of cards when different flu strains infect the same animal. Other pathogens carry all their genetic material on a single DNA or RNA molecule making such gene shuffling between strains less likely, but it still happens. Also, the mutation rate of a pathogen’s genome is a function of its replication rate; hence, each time a bug copies its genome, small random errors are inserted into its genetic code. The more the bug replicates, the more mutations will accumulate in its genome and the faster replicating bugs will more rapidly create new variants. Thus, the measles virus is pretty stable since it does not replicate as much as a coronavirus or a flu virus, so it is not surprising that vaccine immunity to measles is much more durable. Smallpox and polioviruses also have relatively low replication rates and vaccine immunity to them also is long-lasting. In contrast, flu and coronaviruses replicate rapidly and pass back and forth between humans and animals. This means that they mutate rapidly and need frequent vaccine updates.

Other vaccines, such as the TB vax, target bacteria not viruses. Bacteria carry larger genomes that are not so changeable, so anti-bacteria vaccines also are pretty long-lasting compared to many anti-viral vaccines.

Yet other vaccines, such as those against tetanus, diphtheria, and pertussis do not even target the pathogen at all, but target toxins produced by the bugs. Vaccinated people produce antibodies that neutralize the toxins and this prevents disease. These vaccines do not forestall infection, they simply prevent the ill effects of the pathogen. Therefore, for these toxoid vaccines, there is no immunological selective pressure to select pathogen variants that can avoid vax immunity. Vaccines against these toxins also tend to be among the longest-lived vaccines.

Vaccine immunology. Vaccines aim to mimic natural immunity we develop to infection with pathogens. By exposing the body to harmless imitations of a pathogen, vaccines create an immune response and immune memory against pathogens, while avoiding the disease caused by the bugs. When an infection does occur in a vaccinated person, a rapid and robust immune response is mounted, first with B-cell generated antibodies that latch onto the invaders and prevent them from spreading and causing illness. Then T-cells secret cytokines that further ramp up the inflammatory response, and other T cells attack pathogen-infected cells. As explained earlier in these pages, antibody responses tend to linger only a few weeks to a few months and then gradually decay. This is good; otherwise your blood serum would be like syrup from all the antibodies against all foreign things you encountered over your lifetime. While antibodies circulating in your blood are good for quickly attacking infections shortly after infection, they do not confer long-term immunity. What confers long-term protection is what are called memory cells. These are a relatively few T and B cells that go dormant after fighting an initial infection or responding to a vaccine, but hang around awaiting a new infection to signal them to quickly roar back to life and mount a vigorous response against their cognate pathogen. This secondary response to a previously seen pathogen is much faster and usually nips the bug in the bud so you don’t even know you were infected.

When we hear that CoV-2 immunity decays only a few months after vaccination, the reports usually refer to declining levels of anti-CoV-2 antibodies, which happens naturally. Such announcements do not take into account your immune memory, which is harder to measure, but which is a better metric of your long term immunity. The problem also is that we simply have not had enough time with the vaccines to know how long their immune memory persists. It seems relevant that a study published in July 2020 reported that people who were infected with SARS in 2003 maintained robust T cell immunity 17 years later. So far, indications are that even though antibody levels fall over time, immunological memory after vaccination also remains robust. This is seen by the continued protection from serious disease and death in vaccinated people with low antibody levels. The vaccines and the immune memory they stimulate are working. How long that memory persists is unknown. Time will tell.

So why are we getting the booster shots? In the face of a raging pandemic caused by a novel pathogen, the cautious approach is to keep antibody levels at a protective level in vaccinated people until we better understand the extent of long-term protection brought on by our immune memory. The boosters, therefore, represent a cautious approach to maintain an effective antibody defense during these still early months of a novel pandemic. We likely will reach a time where world-wide immunity from vaccination and natural infection will give us baseline protection that will render COVID-19 mostly a bothersome disease rather than a life threatening infection. Until then, the boosters are a good idea to help us maintain an effective antibody defense against serious disease.

The natural pathology of measles is instructive here. Even though antibody levels typically decline after most immunizations, antibodies produced after a measles vaccine persist for many years. This happens with some other, but not all, vaccines too, but why? In countries where the measles virus is endemic, repeated infection of vaccinated people keeps the antibody immune response in continual high gear. That is not the case with the flu virus which changes rapidly and bypasses last years shot. Interestingly, measles has been eradicated from the US and Western Europe, so vaccinated people are not continually exposed and re-exposed to the virus and, unlike for those who live in endemic areas, our anti-measles antibody levels decline. Therefore, our long-term protection against the virus is due to our immune memory and not due to antibody levels.

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