Thursday, August 20, 2020

What is Known and Not Known about the Virus SARS-CoV-2 After Seven Long Months?

 Environmental & Science Education, STEM, Health, Medicine

Ed Hessler

Covid is now seven months in. What do we know and what questions remain about Covid-19? Andrew Joseph, Helen Branswell and Elizabeth Cooney of STAT provide some insights. The essay is long but it reflects the importance of the pandemic in our lives. Some of the findings and a few notes below but not all that is reported.

--Covid and kids: It’s complicated. In spite of the spin doctors, many of whom are politicians kids can contract the disease. The authors write, " We’ve learned younger children and teenagers shouldn’t be lumped together when it comes to Covid. Teens seem to shed virus — emit it from their throats and nasal passages — at about the same rates as adults. Kids under 5 have high levels of virus in their respiratory tracts, but it’s still not clear how much they spread it or why they don’t develop symptoms as often as adults do." And the rates of infection have risen from the outset of the pandemic.

--There are safer settings, and more dangerous settings. The worst settings include these characteristics: close, long, indoors, loud talking, heavy breathing, singing. "[T]here is a threshold level of virus you need to be exposed to to become infected. Also, one hypothesis for why some people get so sick is that they are exposed to higher “doses” of virus.

 --People can test positive for a long time after they recover. It doesn’t matter. This may come as a surprise..

--After the storm, there are often lingering effects. Covid-19 misses no body system or part. The authors discuss three: brain, heart, peripheral nervous system.

--‘Long-haulers’ don’t feel like they’ve recovered. Some people who survive don't feel like their old selves. They are called the 'long-haulers.'  "Mount Sinai Health System in New York City opened a Center for Post-Covid Care in May to treat long-haulers. David Putrino, director of rehabilitation innovation there, has suggested dysautonomia — when heart rate, blood pressure, and body temperature are disjointed —could be to blame for prolonged and distressing symptoms. Why Covid-19 would cause this isn’t known, nor is the best treatment."

--Vaccine development can be accelerated. A lot. It was good news when it was learned that vaccine trials could be "compressed and overlapped."

--People without symptoms can spread the virus. These people are referred to as asymptomatic and presymptomatic--will show symptoms but haven't yet. There is a percentage of infected people, estimated to be about 20% do not show any symptom.  "Whether or not someone is asymptomatic or presymptomatic, they can still spread the virus (though whether they spread it as efficiently as people with symptoms is still unknown). That is why public health campaigns have been stressing distancing, masks, and hand hygiene for everyone, not just people who feel sick."

--Mutations to the virus haven’t been consequential. Other virus families mutate quickly. This means vaccine development moves more quickly since the SARS-CoV-2 vaccines are based on its genetic sequence. There has been one exception: the "G variant." This involved "one swap in the “'letters'” that make up the virus’ RNA."  The switch occurred early and the so-called "G-variant" is now dominant. It is not know whether this happened just by chance or whether it is more contagious.

--Viruses on surfaces probably aren’t the major transmission route. Surface germs are known as "fomites." "(Maria)Van Kerkhove of WHO said there hasn’t been a case recorded where it’s clear someone was infected by fomites alone." However, do NOT stop cleaning surfaces and washing hands though. These are "risk-lowering step(s) people can take, public health officials agree."

--People seem to be protected from reinfection, but for how long? So far "scientists have not confirmed any repeat Covid-19 cases," but much is not known about the body's immune response and whether/how long it confers immunity. T-cells are the body's response team to pathogens but their role in Covid-19 has not been established. 

--What happens if or when people start having subsequent infections? It is well known and our personal experience that respiratory viruses "don't induce life-long immunity in the way a virus like measles does." It is not known whether reinfections might mean a lesser threat than the first one. One study in the Netherlands, preliminary and not yet peer-reviewed "followed people for decades, measuring their antibodies to four human coronaviruses at regular intervals and looking for changes that would indicate a new infection. The scientists found that reinfection could occur within a year of the first infection."

--How much virus does it take to get infected? This is among the greatest unknowns. "Angela Rasmussen, a coronavirus expert at Columbia University said “'We don’t know the amount that is required to cause an infection, but it seems that it’s probably not a really, really small amount, like measles.'” 

--How many people have been infected? "Problems with testing, and its limited availability, have contributed to (the gap between confirmed cases and carriers), as has the fact that some people have such mild or no symptoms that they don’t know they’re infected. But researchers don’t know just how big of a gulf they’re dealing with — how much spread they’ve missed.

--It’s not clear why some people get really sick, and some don’t. Consider the range: "from a truly asymptomatic case, to mild symptoms, to moderate disease leading to months-long complications, to death." There are clear factors: being old, underlying health conditions (cancer, obesity, sickle cell disease) and possibilities: genetic differences, blood types, T-cells that formed as a result of "one of the common cold-causing coronaviruses but that can recognize SARS-CoV-2 as well (referred to as "cross-reactive" T cells). Up to half of us have them but do they actually play a role in whether we get sick or less sick from SARS-CoV-2 is not known. It remains a tantalizing hypothesis.

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