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We have now been living with SARS-CoV-2, the virus that causes covid-19, for the best part of a year. In that time, our knowledge has expanded dramatically, but there is still so much we don鈥檛 know 鈥� and even when we think we know things, the science can change fast.

On 24 September, we held a live Q & A event online for subscribers about the pandemic and were inundated with questions. Here, our reporters tackle some of the most common.

Transmission

How does the coronavirus spread through the air? Is aerosol transmission a possibility?

The coronavirus definitely infects people via the air. The rather confusing debate among experts is whether it is only carried by large droplets that rapidly sink to the ground or whether people can also be infected by smaller droplets that can remain airborne for hours, known as aerosols.

It is very hard to establish exactly how people have been infected, but the overall evidence does suggest that aerosol transmission is happening. To give one example, a concluded: 鈥淭he most likely route of transmission during the flight is aerosol or droplet transmission.鈥�

What about aerosols indoors? I鈥檓 wondering if I brave a museum visit.

The risk is thought to be greatest in crowded, poorly ventilated spaces where people don鈥檛 wear masks and shout or sing, such as some pubs. In a spacious museum that isn鈥檛 crowded and where everyone is wearing masks, as currently required in the UK, the risk should be lower. However, the risk also depends on the odds of encountering infectious people. If case numbers are rising, these odds rise too. How you travel to the museum will also matter.

And how about outdoors?

The risk will vary enormously depending on circumstances, such as how windy it is, how many people are around you, how close they are and if any are infectious. Time is also a factor: you might have to stay in close proximity to an infected person for some time to breathe in a high enough dose of the virus to infect you.

Are HEPA filters highly beneficial?听

High-efficiency particulate air (HEPA) filters should remove most tiny, floating aerosol particles that might contain viruses. These are now recommended for filtering recirculated air in ventilation systems for public spaces. All passenger aeroplanes should have them, for instance, which might help explain why there are relatively few confirmed cases of people being infected while flying. But we don鈥檛 know how much difference they have made.

How long does the virus remain active on surfaces?

After reviewing the scientific literature, Emanuel Goldman at Rutgers University in New Jersey concluded that the . 鈥淭he focus should be on masks, social distancing and doing things outdoors as much as possible,鈥� he says. 鈥淚nanimate surfaces are a very minor player in all this.鈥�

Don Schaffner, also at Rutgers, says he has found only one case providing evidence of transmission via surfaces, or fomites, in the peer-reviewed literature. It was for two individuals who sat in the same seat in Singapore. But he says by all means mitigate the risk by using hand sanitiser and washing hands regularly. 鈥淚鈥檓 not telling people to not worry about surfaces,鈥� he says. 鈥淚鈥檓 saying worry first about other people.鈥�

A paper published on 7 October found that on non-porous surfaces, such as glass touchscreens, stainless steel and paper banknotes. The Australian team behind the research agreed that the virus spreads mainly through aerosols and droplets in the air, but concluded that surfaces may be an important route too because the virus 鈥渃an remain infectious for significantly longer time periods than generally considered possible鈥�. However, real-world differences in temperature, humidity and sunlight 鈥� the virus samples were tested in a lab in the dark 鈥� mean the results don鈥檛 reflect real-life situations.

Is disinfection of surfaces worthwhile and, if so, with what?

At home, disinfect surfaces just as much as you would normally. Soap and water are fine, says Goldman. He says he hears of people sanitising their mail and wiping down their groceries. 鈥淚t鈥檚 a good idea to wash your hands after you come back from the grocery store,鈥� he says, but sanitising your food is unnecessary.

Are masks an effective measure? Is there a need to wear one outdoors?

A growing number of studies suggest that face coverings reduce your chance of getting infected, make infections less severe if you do get infected 鈥� by reducing the amount of virus you are exposed to 鈥� and stop you infecting others if you have caught the virus. No single study is conclusive, but looked at as a whole, the evidence is convincing. Even when there is no requirement to wear face coverings outside, it is still a good idea in crowded places where you cannot avoid being close to others.

鈥淭he focus should be on masks, social distancing and doing things outdoors as much as possible鈥�

Is wearing masks for long periods of time detrimental for children鈥檚 health?
Young children shouldn鈥檛 wear masks. The World 91色情片 Organization (WHO) says that children aged 5 years and under shouldn鈥檛 be required to wear them, and . In England and Wales, children under 11 don鈥檛 have to wear masks, in Northern Ireland it is the under 13s and in Scotland the under 5s. There are also exemptions for people who find wearing or removing masks distressful. There have been claims spreading on social media that it can be harmful to wear masks for long periods, but doctors say this isn鈥檛 true. As long as you can breathe comfortably after you put a mask on and it remains dry, how long you wear it shouldn鈥檛 matter.

Vaccines

What is the progress on developing a universal coronavirus vaccine?

Never before in vaccine history has so much progress been made in such a short time. Several vaccines are already in phase III trials to see if they actually work, and dozens more potential vaccines are being developed. Vaccine manufacturers are also being paid to prepare for making billions of doses. Hopes are high, but even if several vaccines prove effective, it will take years to roll them out worldwide.

Will the first vaccines benefit the most vulnerable?

Older people have a lower immune response to vaccines and so flu vaccines for them contain added components called adjuvants that boost the immune response. We don鈥檛 know whether this will be necessary for the coronavirus, but the Novavax vaccine already in phase III trials contains an adjuvant, and several other vaccines with adjuvants are in earlier stage human trials.

If several strains of the new coronavirus emerge, can we expect any vaccine to be completely effective?

There are many reasons why vaccines might not be 100 per cent effective, unfortunately. For instance, they might not produce a strong enough immune response. The differences between coronavirus variants are small, so the hope is that any one vaccine will work against all of them. If this doesn鈥檛 prove to be the case, however, it should be possible to tweak vaccines so they protect against multiple variants, just like flu vaccines typically do.

How much time would have been saved in the development of a vaccine by doing challenge trials, versus the traditional approach?

With challenge trials, healthy people are given the coronavirus to test a vaccine鈥檚 efficacy. These might be able to give results in weeks instead of months or years 鈥� at least for young people. No one is proposing challenge trials involving older or vulnerable people, though, so they wouldn鈥檛 tell us how well any vaccine works for these key groups.

Would there be any advantage to being given more than one vaccine at the same time as they become available, since no one vaccine promises to offer blanket protection or be 100 per cent effective?

We don鈥檛 yet know how well any vaccine will work 鈥� some might completely protect against infection. It would also be unethical for anyone to get two vaccines while supplies are limited. Besides, the key ingredient in many vaccines is the coronavirus spike protein. If two different vaccines contain the same version of the spike protein, receiving both at the same time is unlikely to provide any advantage. However, getting a second shot a few weeks or months later might boost the immune response. This is why many candidate coronavirus vaccines involve two doses given a few weeks apart.

Treatments

With improvements in treatment, how has the fatality rate for covid-19 changed?

We have a good idea of how many people have died in richer nations. What we don鈥檛 know is how many have been infected, as the number of reported cases isn鈥檛 the full story. So there is no definitive way to calculate the infection fatality rate (which estimates the proportion of deaths among infected people) or how it is changing 鈥� estimates still . Figures from the UK鈥檚 Intensive Care National Audit & Research Centre suggest that 83 per cent of people admitted to intensive care units after 1 September are surviving compared with 60 per cent before this date, but these numbers must be . Intensive care units might have turned away more borderline cases during the first peak due to a lack of resources, for instance, making the apparent death rate higher then.

Is plasma therapy likely to be effective?

In theory, there is every reason to think that treating covid-19 patients using blood plasma taken from people who have recovered from the disease will work. And several small, early studies have reported promising results. But we need to wait for the results of large trials because the complexity of biology often confounds expectations. For example, it has just been discovered that a tenth of people with severe covid-19 made by their own bodies 鈥� a kind of autoimmune response. Plasma donated by these individuals could make the disease worse.

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Testing

Is it realistic for the UK to increase testing capacity to the level required to have adequate surveillance and quick contact tracing?

Experts think testing can be ramped up if the UK government expands beyond its current largely centralised approach. This means providing support to smaller labs, says Charles Swanton at the Francis Crick Institute, for instance by providing them with IT solutions and support to work with hospitals, care homes and communities. A new lab near Loughborough 鈥� one of the 鈥淟ighthouse Labs鈥� that forms part of the backbone of UK testing 鈥� should add capacity for an extra 50,000 tests a day by the end of the year.

Swanton says better contact tracing is vital if greater testing is to be effective at slowing the epidemic. Contact tracing in England is failing to keep up with demand. Figures show that 31.4 per cent of contacts, or almost 32,000 people, weren鈥檛 reached, the lowest since the scheme began in May. 鈥淚mproving contact tracing, both forwards and backwards, to establish how the index case was infected in the first place will be a central and essential part of efforts to increase testing capacity,鈥� says Swanton. 鈥淲ithout an efficient contact-tracing infrastructure and 24-hour test turnaround, increasing capacity will be associated with only marginal gains.鈥�

Origins

Are we any wiser about the origins of SARS-CoV-2?

We still don鈥檛 know for sure where the virus came from, and we may never know. But by far the most likely source is a bat.

That is based on the virus鈥檚 two closest-known genetic relatives, which are coronaviruses isolated from horseshoe bats in China. The closest of all is BatCoV RaTG13, which was isolated from a species called the intermediate horseshoe bat (Rhinolophus affinis) in 2013 and shares 96 per cent of its genome with SARS-CoV-2. Next closest, on 93 per cent, is BatCoV RmYN02 from a Malayan horseshoe bat (Rhinolophus malayanus). But neither virus is the direct recent ancestor of the new coronavirus.

Even a 4 per cent genetic difference represents decades of separate evolution. One recent analysis of the differences between SARS-CoV-2 and BatCoV RaTG13 that they diverged about 50 years ago. Only the discovery of a much more closely related virus in a wild bat will confirm the bat origin story.

It is also possible that the source is an intermediate species that caught the virus from a bat and then passed it on to humans. The number one suspects are pangolins, which are also known to carry coronaviruses that are genetically similar to SARS-CoV-2.

Bats and pangolins were almost certainly on sale in the live animal market in Wuhan, China, that has been identified as the pandemic鈥檚 ground zero. So the virus could have crossed the species barrier there, from a bat or a pangolin into a human.

But it is also possible that the market was merely the venue of a superspreader event, not where the virus jumped species. One scenario that cannot be ruled out is that a progenitor virus acquired from bats was circulating in humans for months causing only mild symptoms, but then mutated into SARS-CoV-2 and began spreading in the market.

Another scenario that cannot be completely ruled out is that the virus accidentally escaped from a laboratory, specifically, the Wuhan Institute of Virology, which is known for its high-quality research on bat coronaviruses. However, this is highly unlikely as it would mean the lab had been working on a bat virus very closely related to SARS-CoV-2, and no such virus has been reported in the scientific literature.

There is also the sinister possibility that the virus was deliberately engineered in a lab as a bioweapon, but a non-peer-reviewed paper was recently dismissed听by mainstream scientists.

Why are bats the reservoirs for so many viruses?

Bats are clearly trouble: they also gave us the original SARS virus, plus Ebola, Nipah and more, and are by far the most prolific source of zoonotic viruses, ones originating in animals. Bats can tolerate extremely high virus loads, meaning that they are an efficient incubator of novel viruses. Humans also come into contact with bats relatively frequently, especially in parts of the world where they are a source of meat and traditional medicines.

What is the relationship between this virus and the original SARS virus?听

The scenario that the new coronavirus passed through an intermediate species and then into humans tallies with what we know about the origin of SARS-CoV-1, which caused an epidemic of a new respiratory disease, severe acute respiratory syndrome (SARS), in 2002-03. After years of detective work, virologists now know that it originated in bats and was passed to humans via palm civets.

SARS-CoV-1 is the closest relative of SARS-CoV-2 known to infect humans. Both are classified in a sub-lineage of the coronaviruses called sarbecoviruses (the MERS virus, the next-closest, is in a different sub-lineage). However, they are still quite distantly related: their genomes are only about 80 per cent identical.

Immunity

At least one person who had covid-19 a second time had a more severe illness. Could we have issues vaccinating people who have had it?

Fortunately, it is now becoming clear that exposure to the virus provokes a classic immune response that protects people against reinfection. However, we don鈥檛 know how long immunity lasts. It may only be months.

There are a handful of confirmed cases of reinfection, but nowhere near as many as would be expected if the immune response always fades rapidly. It is possible that the people who got reinfected had an unusually weak response the first time or encountered a mutant virus that was biologically different enough to evade their so-called immune memory. The test results could also have been false positives.

At least one person who had covid-19 twice is reported to have , which raises the spectre of something called 鈥渄isease enhancement鈥�. This is where a second bout of an infectious disease is worse than the first. A few viruses, most notably dengue, are known to do this, but it is too early to say whether SARS-CoV-2 does too.

鈥�28 days
The amount of time the virus might remain stable on touchscreens鈥�

There is a similar phenomenon called 鈥渧accine-enhanced disease鈥�, where a vaccine not only doesn鈥檛 protect against infection, but also makes the symptoms of the disease worse. Vaccine developers are well aware of this risk. Thankfully, it hasn鈥檛 been spotted in any of the experimental vaccines so far. This also suggests that reinfections won鈥檛 typically be worse.

It appears that the recent 鈥渟econd waves鈥� of the virus are in different areas from those hit hardest initially. Does this suggest that there is some degree of immunity in places most affected originally?

Antibody surveys are probably not picking up the true extent of immunity to the virus. These tests look for circulating antibodies, which are known to fade quite rapidly after an infection or are hardly produced at all. , for example, found that among UK doctors who had tested positive for the virus, 12 per cent had no detectable antibodies.

The T-cell response, which is the arm of the immune system that kills infected cells, seems to be much more robust. Immunologists think that if we did population surveys of T-cells, we would see higher levels of immunity. This so-called cryptic immunity may be why the second wave is hitting different areas to different extents. But we can鈥檛 be sure.

鈥淚f the immune response fades rapidly, we would expect to have seen more cases of reinfection鈥�

Is there any evidence that previous exposure to other coronaviruses provides the immune system with any defence against covid-19?听

There are four seasonal coronaviruses in general circulation, and they usually cause nothing worse than a common cold. There is emerging evidence that exposure to any of them can induce some immunity to SARS-CoV-2. Laboratory experiments suggest that this is mediated by the T-cell response, which is the part of the immune system that kills virus-infected cells. Even though the new coronavirus and the cold viruses are quite distantly related, they share some molecular features that invoke a T-cell response and produce 鈥渃ross reactivity鈥�. It isn鈥檛 clear whether these cold-killing T-cells can also destroy cells infected with SARS-CoV-2, but their presence seems to make the infection much less severe.

This is probably why some people who have definitely been in contact with SARS-CoV-2, for example via a close family member who lives in the same house and has fallen ill and tested positive, don鈥檛 develop covid-19 and never test positive for the virus. But we know that the immune response to cold-causing coronaviruses fades quite quickly, so any cross immunity will be short-lived.

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Can I predict my personal risk for covid-19?

All sorts of factors, including age, race and pre-existing health conditions, determine your risk of becoming severely ill. Because it still isn鈥檛 clear who will develop an asymptomatic case of covid-19, it is difficult to predict the risk to an individual who hasn鈥檛 yet caught the virus. But once symptoms start, it should, in theory, be possible for an individual to calculate their own personal risk of experiencing a severe or potentially fatal case, says Tim Spector at King鈥檚 College London. There isn鈥檛 yet a 鈥減ersonal risk calculator鈥� available, but Spector鈥檚 team is working on ways to predict risk based on early symptoms and data collected from the COVID Symptom Study app.

At the moment, however, there is no way to predict who is at risk of 鈥�long covid鈥�, where often debilitating symptoms can last for months.

Environment and animals

How is the pandemic related to over-exploitation of the planet?

The role our destruction of nature plays in infectious diseases spilling over into humans is something we have only begun to grasp fully in the past two decades, says Peter Daszak at the Eco91色情片 Alliance. He says the drivers include: rising human population density; encroachment into and road building in forests; and hitting thresholds of contact between wildlife, humans and livestock at which a disease emerges and then spreads through trade and travel networks.

Global analyses have found that the risk of zoonotic diseases emerging is highest in tropical areas where land use is changing, such as forests being cleared for cattle farms.

Daszak also says that the wildlife trade in China readily mixes legally and illegally captured and traded animals, and involves domestic and international commerce 鈥� and that viruses exploit those pathways.

However, it would be wrong to think that people in the West aren鈥檛 also to blame. 鈥淭he encroachment of people into high biodiversity regions is a global driver of emerging infectious diseases and it鈥檚 largely done to supply our overconsumption in richer countries,鈥� says Daszak.

Is it possible for pets to carry and spread the coronavirus?

SARS-CoV-2 has been detected in a number of animals, including tigers, lions and rabbits. Ferrets, hamsters and cats have been shown to be able to pass the virus to others of the same species, and transmission between mink in the Netherlands has led to outbreaks at .

However, cases of pets catching the coronavirus from their owners remain rare, and research indicates that most pets with confirmed infections only show mild symptoms.

Whether animals can pass the virus back to humans is less clear. A hasn鈥檛 yet been peer-reviewed suggests that mink at Dutch farms have transmitted the virus to farm workers. If confirmed, it would be the first documented case of animal-to-human transmission. To date, there are no recorded cases of domestic pets infecting humans.

Journalism

How useful have you found the Downing Street news conferences by the UK government? Is it wise to put scientists on the same platform as politicians?

The briefings have often focused on political questions, such as judgements over balancing competing economic and public health priorities. Generally, they haven鈥檛 yielded a lot of answers on questions about the science or unpublished details of the UK government鈥檚 response to the epidemic, although New Scientist was able to ask questions around contact tracing and symptoms. The briefings are better than nothing. But the format 鈥� where journalists are muted and unable to ask follow-up questions 鈥� limits how useful they are. There are risks that scientists are silenced by politicians, as has happened at some of the briefings. On balance, it is better they are there than not, for transparency and accountability.

Data

How reliable are the figures from the UK鈥檚 Office for National Statistics?

The ONS has tracked weekly mortality figures throughout the epidemic and collates surveys on the social and business impact of covid-19. In April, it also launched a weekly infection survey, which attempts to model current infection rates in the UK by regularly asking people in thousands of homes to take 鈥渉ave you got it鈥� covid-19 tests. For now, it only runs in England and Wales, not Scotland and Northern Ireland. Angela McLean, scientific adviser to the UK Ministry of Defence, views the survey as the gold standard for measuring the state of the UK epidemic.

Sheila Bird at the University of Cambridge says the ONS coronavirus output is a 鈥渕assive effort, highly impressive鈥�. However, she notes that the ONS is handicapped somewhat by the way figures are provided to it. While the cause of death must be registered within eight days of death in Scotland, registration is often much later in the UK鈥檚 other nations, says Bird, causing a delayed picture of what is really happening now.

Finally, it is worth noting there have been concerns over the quality of data being produced during the epidemic. David Norgrove, the chair of official statistics watchdog the UK Statistics Authority, has twice written to health secretary Matt Hancock to complain of testing data that fell short of expectations.

Pandemics

How long do pandemics normally last?

Covid-19 is the second pandemic of the 21st century. The H1N1 influenza outbreak of 2009-10 sickened and killed far fewer people than covid-19 already has. You could argue that there is a flu pandemic every year, yet the WHO saves the term for novel flu viruses, not slightly mutated seasonal ones.

The H1N1 pandemic lasted about a year-and-a-half, but that is no guide to how long the current pandemic or future ones will last. The duration of a pandemic depends on the biology of the disease and the measures used to control it. There is also the ongoing HIV pandemic that began in the 1980s.

Other relatively recent pandemics include the 1918 flu, the flus of 1957-58 and 1968-69 and the cholera pandemic of 1961-75. However, history is littered with them, including the worst of them all, the Black Death of 1331 to 1353, which killed up to 200 million people out of a global population of about 450 million. By comparison, we could consider ourselves lucky.

Is there really any hope that the coronavirus will be defeated or will we have to live with it forever?

Many infectious disease experts believe we will have to learn to live with it. Global social inequalities and air travel imply that so long as the virus exists in people somewhere in the world, its easy transmission means it will spread.

Even if a vaccine is developed, it doesn鈥檛 mean that the world is likely to 鈥渂eat鈥� or eliminate the virus. 鈥淲hat will a vaccine do? It certainly won鈥檛 stop it becoming endemic,鈥� says David Heymann at the London School of Hygiene & Tropical Medicine. 鈥淲e don鈥檛 understand enough about immunity to understand what that vaccine might be and if herd immunity can be established.鈥�

Do you think experience of this pandemic will help better prepare us for future ones?

Despite a decade of warnings from the WHO that a new pandemic was a certainty, covid-19 caught the world napping. Experts say there will be another pandemic sooner or later, but we are unlikely to be any better prepared for it despite our current predicament.

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Reporting a pandemic
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