virus news … (+ some dark humor)

from US man, 30, dies from virus after attending ‘COVID party’

https://www.yahoo.com/news/us-man-30-dies-virus-attending-covid-party-230251335.html

A 30-year-old man who believed the coronavirus was a hoax and attended a “Covid party” died after being infected with the virus, according to the chief medical officer at a Texas hospital.

The official, Dr. Jane Appleby of Methodist Hospital in San Antonio, said the man died after deliberately attending a gathering with an infected person to test whether the coronavirus was real.

In her statements to news organizations, Dr. Appleby said the man had told his nurse that he attended a Covid party. Just before he died, she said the patient told his nurse: “I think I made a mistake. I thought this was a hoax, but it’s not.”

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‘The curve is no longer flat’: Nearly half of Florida’s ICUs are at least 90% full

https://www.usatoday.com/story/news/health/2020/07/09/coronavirus-florida-nearly-half-states-icus-least-90-full/5409773002/

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from An ICU boss in the hardest-hit part of Italy says many patients who recover from COVID-19 still have ‘chronic damage’

https://www.businessinsider.com/head-icu-bergamo-italy-epicentre-lifelong-damage-recovered-covid-patients-2020-7

He did not specify how many were affected. Several studies have shown problems in patients who had COVID-19 but have yet to reach firm conclusions.

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A July 8 study from University College London observed delirium, rare brain inflammation, and strokes in recovered COVID-19 patients.

Issues with the gut, heart, and kidneys have also been reported after recovery, Independent reported, citing doctors and researchers. Experts are also concerned about effects on the mental health of severely ill patients.

You can’t get more disingenuous than she is here. You just can’t. https://t.co/9ur6xtM8Wt

— Joe Walsh (@WalshFreedom) July 22, 2020

Stephen Miller, a top adviser to President @realDonaldTrump, is insisting his grandmother did not die of the #coronavirus, despite a death certificate that states otherwise.https://t.co/o0KkkNnqkx

— The Jerusalem Post (@Jerusalem_Post) July 24, 2020

JUST IN: Experts who sounded the alarm to Trump administration officials about the gathering coronavirus crisis break their silence, offering a searing assessment of how the federal government blundered through the critical first months of the outbreak. https://t.co/VT0uePJkWd

— ABC News (@ABC) July 28, 2020

76% of covid survivors in one study (2/3 of whom were never hospitalized) hearts were damaged as if they’d had a heart attack https://t.co/srvAtIcEJV

— Nick Riccardi (@NickRiccardi) July 29, 2020

My man is checking-in with different countries regarding their coronavirus numbers…😂😭🤣 pic.twitter.com/mpkDYMTI1B

— Rex Chapman🏇🏼 (@RexChapman) July 31, 2020

from Facebook

Mike Silverman

Friday night update from the ER in Arlington, VA

150,000 deaths in the US from COVID. 1000 deaths a day. We are normalizing huge amounts of our citizens dying. Maybe we are doing this because it’s not hitting close enough to home for us. A Baltimore ICU doctor died of COVID this past week after a prolonged hospitalization. Middle aged. Putting himself on the front lines to care for patients. I have a good friend who worked with him for years. And a doc associated with VHC died recently of COVID as well. Just two of almost 1000 healthcare workers to die of COVID. It’s close to home for me.

I get texted/messaged about every other day from a friend with a question about a COVID exposure. Given our ages, it’s usually their kid was at a bar with someone who tested positive the next day. Sometimes, they were with a friend out to lunch who tested positive a few days after the lunch and people want to know what to do. Recently, 17 anesthesia residents at the Univ of Florida were at a party together and came down with COVID. There are many other examples of large numbers of people who became sick after large group gatherings. I talked about what to do after these exposures recently (quarantine/test) but keep in mind, these are generally preventable exposures with social distancing and mask wearing. The sacrifices we make now will bring this pandemic to an end much quicker so we can get back to normal.

Let’s talk about COVID at VHC for a minute. There’s some good news and a couple of things we’re closely following. We continue to be in a steady state. The percent positive rate for our COVID cases across the board remains low and has been in the same range for about a month. The number of hospitalized patients with confirmed COVID has been in the same range for a while, though numbers continue to increase across the DMV. In the ED, we’ve been tracking the numbers of patients who require our COVID isolation procedure. The total number of patients being admitted from this group has also remained steady for over a month. However, we’ve seen an uptick in the numbers of patients who require a COVID evaluation, seeing about 20% more patients who are considered to possibly have COVID than the previous several weeks, with a higher total number of them being discharged last week compared to previous weeks. We are far from any kind of surge but all of these data points are closely monitored and will help us prepare if and when another surge occurs.

At my recent department meeting, we had the director of the ICU join us. She talked about the improvements in treatment that had led to a decline in mortality and the indications for the different medical therapies she can offer patients. Some important national mortality numbers to keep in mind—about 50% of intubated (ventilator) patients die, 30% of ICU patients die, and 10-15% of hospitalized patients die. While many patients have risk factors, age 50 or older increases your risk, as does a BMI>30. That is not nearly as obese as you think. 5’6” 186 pounds or 6’ at 221 pounds.

In what I can only call irony, it appears that at least 3 people may have contracted COVID or transmitted COVID while they were taking the MCAT (like the SAT for med school) recently. One test taker, had symptoms of COVID and still took the exam. Exams are administered at testing centers and in a post-exam survey, some test takers said there was limited screening and/or the ability to social distance during the test. Exams were cancelled in different areas and like other standardized testing that has limited offerings, like the Bar for lawyers, intelligent, motivated people who have prepared for months will not let anything stop them from taking this test. Everyone needs to take precautions regardless of how important your life is.

Finally, hydroxychloroquine made the news again this week. I had really planned on going into the prospective, randomized peer reviewed studies today but there was a great post yesterday that included all the references, so I shared that instead. You don’t need to watch the video from the doctor who endorses aliens and sex demons. With that said, there was a recent New England Journal publication earlier this month—prospective, randomized, trial for patients with mild to moderate COVID, where patients received standard treatment compared to hydroxychloroquine with and without azithromycin. At 15 days, there was no difference in the groups though adverse affects (EKG changes and bump in liver enzymes) were higher in the 2 arms that got hydroxychloroquine. The good news, is that we do have medications that are actually making a difference. I’m optimistic there will be more, but we’re in a better place than we were 6 months ago, even without hydroxychloroquine and mortality rates really have improved since the beginning.

One other recent New England Journal publication worth mentioning was on the phase 1 trials of a vaccine. There’s still a long way to go but development of a vaccine continues to look promising.

The attached image shows how quickly and broadly COVID spread after a family gathering in North Carolina where 14 family members ultimately tested positive and spread COVID to 41 people in 9 different families and 8 different workplaces over 16 days. This was published by the local county public health director.

Science matters. Wear a mask. Practice social distancing.

As Covid-19 Cases Surge, Patients Are Dying At A Lower Rate. Here’s Why

https://www.latimes.com/california/story/2020-08-09/covid-19-coronavirus-survival-rate-improves

When the number of people being sent to the hospital with COVID-19 began to creep up in Los Angeles County early this summer, officials warned that a major increase in deaths was inevitable. A record-breaking number of cases could result in a record-breaking number of deaths, they predicted.

But nearly two months later, that has not materialized. The coronavirus continues to kill hundreds of people every week in L.A. County, but the death toll has remained lower than expected.

The trend is due in part to younger people falling sick, as well as better control over the disease’s spread in high-risk settings, such as nursing homes. But doctors say there’s another factor pushing up survival rates: better treatments.

“It was so grim in the beginning,” said Dr. Armand Dorian, an ER physician and chief medical officer for Verdugo Hills Hospital at USC. “Now we actually have regimens of treatments that do help. … Since the beginning, say, February to now, we’ve learned a lot.”

The trends are not limited to L.A. County. In California, 3.6% of people diagnosed with COVID-19 between March and May died of the disease. Among those diagnosed between June 1 and Aug. 3, that figure dropped to 1.2%, according to a Times analysis of state data. Expanded testing, changing patient demographics and better patient care all played a role in that drop, experts say.

The statistic is what epidemiologists call the case-fatality rate: the number of deaths divided by the number of cases. This measures how deadly the disease is once people catch it — the chance of surviving. While the pandemic remains bleak, the lowered case-fatality rate is a glimmer of progress, experts say.

The case-fatality rate exists alongside another statistic: the mortality rate — deaths divided by the total population — which reflects the spread of the disease within the population.

In an interview with Axios released last week, President Trump discounted the nation’s mortality rate, which is worse than most other countries’, while lauding its case-fatality rate, which is better than most countries’.

But an improved case-fatality rate cannot offset the vast spread of the deadly virus, experts say. California’s mortality rate is rising as the state’s death toll from COVID-19 surpassed 10,000 on Thursday. If many people keep falling ill, then many people will die, even with improvements in survival rates.

Dr. Tim Brewer, an infectious disease specialist and epidemiologist at UCLA, said that even the medical improvements could be negated if the number of patients continues to grow. An overwhelmed healthcare system could hamper physicians’ ability to provide lifesaving care, he said.

“We’ve acquired a tremendous amount of information in the last seven months that has been helpful. We just need everybody to recognize that the virus has not gone away,” Brewer said.

When COVID-19 patients first began showing up in hospitals in the spring, doctors didn’t know which medicines or treatments would be effective. Little was understood about how the virus was transmitted or the best way to protect staff. USC’s Dorian described healthcare workers dealing with that unprecedented crisis as “deer in headlights.”

But that has changed rapidly as doctors around the world study and treat the coronavirus. Research findings in one country may within days become clinical guidelines in another.

“The collaboration between physicians all over the world over how to best treat COVID-19 has been quite extraordinary,” said Dr. Bilal Naseer, a critical care doctor in Sacramento with CommonSpirit Health, a large nonprofit hospital system. “I think the confidence level of physicians and healthcare teams is very high now — how to early-identify patients with COVID-19 and how to prevent severe disease is really much better understood.”

Early in the outbreak, panicked healthcare workers administered multiple drugs to patients to try to save them, unsure which may help. But that strategy made it hard to tell what was and wasn’t working, so physicians couldn’t gain knowledge they could use to help the next patients.

“Physicians around the world and in L.A. were basically throwing anything we could at these patients,” Brewer said. “We needed to get our panic level down a little bit and do research and trials and studies.”

One of those studies, conducted by British scientists, led to a surprising finding. For other deadly coronaviruses, such as SARS and MERS, steroid medications had been shown to worsen symptoms.

But the UK researchers found that dexamethasone, a common and low-cost steroid, reduced mortality for patients on ventilators by a third, and by a fifth for those requiring oxygen, according to the study published in June.

Doctors had already begun administering remdesivir, an antiviral medication developed by Gilead Sciences, that had been shown to shorten the time it takes for patients to recover from the infection. Both medicines are now regularly prescribed by physicians treating COVID-19 patients, they say.

“We’re miles away from having real cures like vaccinations and more specific meds,” Dorian said. “But we have something. It feels good to say, ‘Why don’t we give remdesivir?’”

San Diego State University epidemiologist Eyal Oren pointed out that many people who get sick may not die, but will still endure long-term health consequences. He warned that looking at small improvements in survival rates may elide the reality that thousands continue to die from COVID-19, particularly people of color.

“Why do we have this many cases and this many deaths?” he said. “What’s the big picture?”

But for some, the improved survival rates are a sliver of hope.

Before the latest wave of patients in L.A. County, the most people ever hospitalized with COVID-19 in the county at one time was just over 1,950 in late April. That record was broken in July, when more than 2,200 people were hospitalized with the infection.

Yet, average deaths never exceeded what they had reached in the spring. The county’s case-fatality rate from COVID-19 has dropped from 4% in May to 2% now, according to county data.

“To me, that probably means we’re doing better care,” said Dr. Jeffrey Gunzenhauser with the L.A. County Department of Public Health.

Gunzenhauser said that the decline is probably also due to changes in who is falling ill. Infections have fallen in nursing homes, whose residents are particularly vulnerable to the virus, while cases have increased among young people, who are healthier and more likely to survive, he said.

When patients do end up in the hospital, doctors have new protocols to improve their odds of survival. Early in the pandemic, doctors rushed to put patients on ventilators when they were struggling to breathe.

But now it has become clear that it may not be necessary to intubate these patients, which can open them up to other complications that actually decrease their chance of survival.

Now, physicians lie patients on their stomachs to allow more oxygen into their lungs and give them oxygen through tubes inserted into their nose. Patients are put on ventilators as a last resort, doctors say.

“We were on a hair trigger to put people on vents at the beginning of the epidemic,” said Bradley Pollock, the chair of the department of public health sciences at UC Davis. “If someone looked like they were declining, we’re going to immediately put them on a vent — that was a mistake, in retrospect.”

Doctors have also learned that COVID-19 tends to thicken patients’ blood and form blood clots, which can cause strokes and heart attacks. In some U.S. hospitals, clots were once reported to be the cause of 40% of COVID deaths. Now doctors know to administer anti-coagulants to prevent these deaths.

The knowledge gained over the last several months has improved care simply by making staff more confident, Dorian said. Patients benefit when healthcare workers aren’t stressed and can take their time with them and listen to their needs, he said.

“That’s what turns people around. It’s not just medicine, really,” he said.

Alex Kirshner@alex_kirshner
Hi, I’m a college administrator who makes $150k a year. I spent the last two months telling reporters, “We’re really banking on our students making smart decisions this fall and not partying.” Now we have 12 COVID clusters after two days. I have no idea how this happened.

Worst pandemic of our lifetime and the Fox News is elevating someone who wants us to know that the pandemic is over.

pic.twitter.com/WTJhv1lLPm

— Molly Jong-Fast🏡 (@MollyJongFast) August 20, 2020

Seven months later, what we know about Covid-19 — and the pressing questions that remain

link https://www.statnews.com/2020/08/17/what-we-now-know-about-covid19-and-what-questions-remain-to-be-answered/?fbclid=IwAR3XPSIRhwjuW-wX6EjF96nr29kH4xQDBoTGYQnwpQor0yuQj0UP5QtrKBc

The “before times” seem like a decade ago, don’t they? Those carefree days when hugging friends and shaking hands wasn’t verboten, when we didn’t have to reach for a mask before leaving our homes, or forage for supplies of hand sanitizer. Oh, for the days when social distancing wasn’t part of our vernacular.

In reality, though, it’s only been about seven months since the world learned a new and dangerous coronavirus was in our midst. In the time since Chinese scientists confirmed the rapidly spreading disease in Wuhan was caused by a new coronavirus and posted its genetic sequence on line, an extraordinary amount has been learned about the virus, SARS-CoV-2, the disease it causes, Covid-19, and how they affect us.

Here are some of the things we have learned, and some of the pressing questions we still need answered.

Covid and kids: It’s complicated

Early in the pandemic, it looked like there was a silver lining to the disease cloud sweeping across the world. Children, it seemed, didn’t develop the severe symptoms that were sending adults to hospitals struggling for breath, and they very rarely died. It even seemed that kids didn’t contract the disease at the same rates as adults did.

But everything Covid is complex, and kids are no exception. While deaths among children and teens remain low, they are not invulnerable. And they probably contribute to transmission of SARS-CoV-2, though how much remains unclear.

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.

A recently published report from a Georgia sleep-away camp shows how quickly the virus can spread among kids. The camp had to be closed within 10 days of starting its orientation for camp staffers, because within days of children arriving, kids and staff started getting sick. (The campers ranged in age from 6 to 19.) The camp did not require campers to wear face masks.

A recent report on Covid infections in children from the Centers for Disease Control and Prevention showed that while they remain low, U.S. hospitalization rates for Covid-19 in children have risen since the pandemic started. And one in three children hospitalized with the disease ends up in intensive care. The highest rate of hospitalizations in children was among those under 2 years of age.

Black and Latino children were hospitalized at higher rates than white children. And like adults, children with other health conditions — obesity, chronic lung diseases, or infants who were born premature — are at higher risk than otherwise healthy children.

Perhaps most alarmingly, it’s become clear that a small proportion of children infected with Covid-19 go on to develop a condition where multiple organs come under attack from their own immune system. Called multisystem inflammatory syndrome in children or MIS-C, this condition seems to occur about two to four weeks after Covid-19 infection. Most children who develop this syndrome recover.

There are safer settings, and more dangerous settings

Research has coalesced on a few key points about what types of setting increase the risk that an infectious person will pass the virus to others.

Essentially, the closer you are to someone infectious and the longer you’re in contact with them, the more likely you are to contract the virus, which helps explain why so much transmission occurs within households. Being indoors is worse, particularly in rooms without sufficient ventilation; the more air flow, the faster the virus gets diluted. Everyday face coverings reduce the amount of virus projected, but aren’t total blockades.

Loud talking, heavy breathing, singing, and screaming expel more virus, which is why experts point to nightclubs and gyms as risky businesses to be open. (That’s not to say it’s impossible to catch the virus while having a quiet conversation with someone outside — it’s just less likely.)

The reason having prolonged, proximate contact with someone is riskier is in part because there is a threshold level of virus you need to be exposed to to become infected. (More on this later.) Also, one hypothesis for why some people get so sick is that they are exposed to higher “doses” of virus.

Researchers are also finding that some relatively small proportion of infected people — maybe 10% to 20% — are driving some 80% of new cases, often through “superspreading” events in indoor settings like bars, meat processing plants, and homes. Whether such transmission occurs depends on a host of variables: how many people are in a given place, what the ventilation in the room is like, and, of course, whether someone with infectious Covid-19 is there. Some people might shed more virus than others, and people are more or less likely to spread the virus during different points in their infection. Evidence suggests that contagiousness spikes in the days before people who will go on to show symptoms start feeling sick.

People can test positive for a long time after they recover. It doesn’t matter

There was a lot of angst a few months ago about some people who had seemingly recovered from Covid-19 infections continuing to test positive for the virus for weeks. Were they infectious? Should recommendations be changed for how long infected people should be isolated?

It turns out it is an issue of testing. Most testing is conducted using a platform called PCR — polymerase chain reaction — that looks for tiny fragments of the SARS-CoV-2 virus. But the test can’t tell if those sections of genetic code are part of actual viruses that can infect someone else, or fragments of viruses that are absolutely no threat.

It’s clear now that people who had mild or uncomplicated infections shed active virus for somewhere up to 10 days after their symptoms started. (“Severely ill or immunocompromised patients do shed infectious virus for longer,” said Malik Peiris, a coronavirus expert at Hong Kong University.)

The weeks and weeks of positive tests — like those that prevented this woman in Quebec from cuddling her infant son for 55 days — don’t tell us that these people are still a risk to others. “In fact, we know that they are not infectious for that long,” said Maria Van Kerkhove, the World Health Organization’s leading coronavirus expert.

After the storm, there are often lingering effects

Name a body part or system and Covid-19 has left its fingerprints there. We know this: Unusually sticky blood can clog vessels on the way to the heart and inside the brain and lungs of infected people, causing heart attacks, strokes, and deadly pulmonary embolisms. There are growing worries that these and other health effects will be long-lasting.

Heart: The hyperinflammation of an immune response triggered by the virus can weaken heart muscles so much that even young people who had mild infections may be at risk for future heart failure, cardiac MRIs in Germany indicate. More immediately, some people have chest pain or feel like their hearts are racing as they recover from the infection. And college athletes are no exception

Brain: People whose first Covid-19 symptom might have been losing their sense of smell and taste may find their anosmia persists. Headaches and dizziness are common. Mood disorders such as anxiety, depression, and PTSD follow in the wake of infection, and the mental confusion called “Covid fog” leaves people searching for words, struggling with simple math, or simply trying to think.

Peripheral nervous system: In Italy, three Covid-19 patients experienced myasthenia gravis, an autoimmune disorder that results in faulty communication between nerves and muscles. Doctors also worry about demyelination, in which the protective coating of nerve cells is attacked by the immune system, causing weakness, numbness, and tingling. In some cases it can spur psychosis and hallucinations. Some patients have Guillain-Barre syndrome, a rare autoimmune disease that interferes with nerve signals, leading to abnormal sensations, weakness, and sometimes paralysis.

SARS-CoV-2, the virus that causes Covid-19, affects more than just the lungs and airways. Here’s how this virus enters cells and the symptoms that can arise from infecting different parts of the body.

‘Long-haulers’ don’t feel like they’ve recovered

They have a name, a growing social media presence, and a problem. They are the “long-haulers,” people who have survived their Covid-19 infections but feel a long way from normal. We know they’re out there, but we don’t know how many, why their symptoms persist, and what happens next.

In July, a survey conducted by the CDC found that 35% of people who tested positive for SARS-CoV-2 and had symptoms of Covid-19 — cough, fatigue, or shortness of breath — but were not hospitalized had not returned to their previous health two to three weeks later. Among those between 18 and 34 years old who had no previous chronic conditions, 20% felt prolonged signs of illness.

The National Heart, Lung, and Blood Institute has launched an observational study to track the long-term effects of Covid-19, aiming to follow 3,000 patients six months after being discharged from 50 hospitals.

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

The world still doesn’t have a vaccine that has been shown to be protective against Covid-19, though China and Russia have issued emergency use licenses for partially tested vaccines.

But an extraordinary amount of progress toward Covid-19 vaccines has been made, in record time. Trials have been compressed and overlapped, with manufacturers running Phase 1/2 trials in some cases and Phase 2/3 trials in others.

Support STAT: If you value our coronavirus coverage, please consider making a one-time contribution to support our journalism.
Meanwhile, they’ve been building out manufacturing capacity to be able to produce hundreds of millions of doses and have started production, even before finding out whether their vaccine candidate actually works. This work is being done with substantial financial support of governments, the Bill and Melinda Gates Foundation, and CEPI, the Coalition for Epidemic Preparedness Innovations.

It’s called “at risk” production — and the term is apt. If some of these vaccines don’t work, that output will have to be junked. But if Phase 3 trials show they do work, deployment could begin as soon as the Food and Drug Administration, or a regulator in another country, approves any of these vaccines.

That means vaccination with fully approved vaccines could begin as soon as about a year after the discovery of the new virus. This constitutes a revolution in vaccine development.

People without symptoms can spread the virus

Discussing asymptomatic cases of Covid-19 automatically raises some headache-inducing semantic issues. Some people are truly asymptomatic throughout their infections, but the word is often also used to describe people who are presymptomatic — those who will show symptoms but haven’t yet. Other people don’t show classic Covid-19 symptoms — fever, cough, loss of smell — but just feel kinda crappy for a day. Where do they fit in?

Whatever group you’re talking about, there are some key implications for the pandemic, and trying to rein it in. One: Some percentage of infected people — roughly 20%, according to one recent review, though other studies have produced higher estimates — do not show symptoms at all. And two: 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. Once you do start showing symptoms and try to restrict contact with others, it is too late to prevent spread.

Mutations to the virus haven’t been consequential

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Viruses on surfaces probably aren’t the major transmission route

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People seem to be protected from reinfection, but for how long?

The thinking is that a case of Covid-19, like other infections, will confer some immunity against reinfection for some amount of time. But researchers won’t know exactly how long that protection lasts until people start getting Covid-19 again.

So far, despite some anecdotal reports, scientists have not confirmed any repeat Covid-19 cases.

All that supports the notion that Covid-19 acts like other viral infections, including illnesses caused by other coronaviruses. Researchers are finding that most infected people mount an immune response involving both antibodies and immune cells that clears the virus, and that persists for some amount of time. Reports of waning antibody levels incited some concern that perhaps protection to SARS-CoV-2 might not last very long, with big implications for the frequency of required vaccine boosts. But immunologists have pointed out that antibodies for other viruses wane as well; their levels surge upon re-exposure to the pathogen and they can still halt reinfection.

When a new pathogen causes illness, the immune system creates memories, so its cells can target and kill the invader if it ever comes back again. Here’s how a person becomes develops immunity.

Researchers don’t know for sure what level of antibodies are required to block the virus from gaining a toehold in cells, and what role pathogen-fighting T cells might have in fending off an infection. People who recover from Covid-19 also produce varying levels of antibodies — it’s possible people who generate a weaker initial immune response might not be protected for as long from reinfection.

“We don’t know for how long that immune response lasts,” the WHO’s Van Kerkhove said last week. “We don’t know how strong it is.”

What happens if or when people start having subsequent infections?

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How much virus does it take to get infected?

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How many people have been infected?

There have been 21 million confirmed cases of Covid-19 around the world, and 5.3 million in the United States. Far more people than that have actually had the virus.

Problems with testing, and its limited availability, have contributed to that gap, 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.

“Serosurveys” — which rely on testing for the level of SARS-CoV-2 antibodies in a community — are starting to help fill in some knowledge. A recent CDC study of 10 cities and states estimated that in most places, the true number of infections was some 10 times higher than the number of confirmed cases.

Still, that leaves perhaps 20% of people, even in hard-hit communities, with potential immunity to Covid-19. That means that herd immunity — the point at which so many people are immune that the virus can’t circulate — remains far off even in areas that have suffered severe outbreaks.

It’s not clear why some people get really sick, and some don’t

The sheer range of outcomes for people who get Covid-19 — from a truly asymptomatic case, to mild symptoms, to moderate disease leading to months-long complications, to death — has befuddled infectious disease researchers.

There are some clear factors for who faces higher risks of getting severely ill: older people, as well as people with conditions ranging from cancer to obesity to sickle cell disease.

But scientists have postulated that a host of other underlying factors could help dictate why most healthy 30-year-olds shake off the virus after a couple days and some get severely ill. Researchers are studying genetic differences in patients, while others are looking at blood type.

Recent studies have pointed to another potential player. Perhaps up to half the population has immune-system T cells that were initially generated in response to an infection by one of the common cold-causing coronaviruses but that can recognize SARS-CoV-2 as well. These “cross-reactive” T cells could help give the immune system the boost it needs to stave off serious symptoms, but researchers don’t know for sure what role, if any, they actually play.