3 things scientists can’t agree on about coronavirus
Face masks
The novel coronavirus spreads by droplets from coughs, sneezes and speaking. To halt the spread of the virus, face masks have become compulsory in many countries.
But there has been much debate among scientists over the effectiveness of face masks on reducing the spread of COVID-19. A report from a multidisciplinary group convened by the Royal Society hascome out in favourof the public wearing face masks. These documents, which have not been peer reviewed, argue that face coverings can contribute to reducing the transmission of COVID-19 if widely used in situations where physical distancing is not possible.
One relatively small clinical study also showed that infected children who wore masksdid not pass on the virusto family contacts.
But the science is complex. Face masks won’t stop the wearer from inhaling small airborne particles of coronavirus, which can cause infection. A recent study reported that wearing amask may also give a false sense of security, meaning wearers may ignore other important infection control measures.
Research has also shown that when people wear masks, the exhaled airgoes into the eyes. This generates an impulse to touch the eyes. And if your hands are contaminated, you may infect yourself. Indeed, WHO warns that masks can be counterproductive unless wearersavoid touching their faceand adopt other management measures.
We also know that face masks can make us breathemore often and more deeply– potentiality spreading more contaminated air.
Many scientists therefore disagree with the Royal Society report, requesting more evidence on the efficacy of masks. Ideally, we need randomised controlled trials involving many people from an entire population to trace how masks affect infection numbers.
That said, other scientists argue that we should use face masks even though perfectly reliable evidence is lacking –to be on the safe side. Ultimately though, without a vaccine, the strongest weapons we have are basic preventive measures such as regular hand washing and social distancing.
Immunity
Immunologists are working hard to determine what immunity to COVID-19 looks like. Much of the studies have focused on “neutralizing antibodies,” produced by so-calledB-cells, which bind to viral proteins and directly prevent infection.
Studies have found that levels of neutralizing antibodies remain high for a few weeks after infection, but then typically begin to wane. A peer-reviewed study from China showed that infected peoplehad steep declinesin levels of antibodies within two to three months of infection. This has created doubt over whether people get long-term protection against subsequent exposure to the virus. If this studyturns out to be accurate– the result needs to be backed up by other studies – it could have implications for whether it is possible to produce vaccines with long-lasting immunity.
While many scientists believe antibodies are the key to immunity, others argue that other immune cells called T-cells – produced when the body encounters the molecules that combat viruses, known as antigens – are involved too. These can become programmed to fight the same or similar viruses in the future. And studies suggest that T-cellsare at workin many patients fighting COVID-19. People never infectedmay also harbor protective T-cellsbecause they’ve been exposed to similar coronaviruses.
A recent study from Karonliska Institute in Sweden, which has not yet been peer reviewed, found that many people who suffered mild or asymptomatic COVID-19have T-cell-mediated immunity– even when antibodies can’t be detected. The authors believe this can prevent or limit reinfection, estimating that one-third of people with symptomless COVID-19 could have this kind of immunity. But it is not clear yet how it works and how long it lasts.
If this is the case, it is very good news – meaning public immunity to COVID-19 is probably significantly higher than antibody tests have suggested. Some have argued it could create “herd immunity” – whereby enough people have been infected to become immune to the virus – with an infection rate as low as 20%, rather than the widely accepted 60-70%. This claim, however,is still controversial.
Immune response to COVID-19 is complex, with the full picture likely to extend beyond antibodies. Larger studies over longer periods of time must now be done on both T-cells and antibodies to understandhow long-lasting the immunity isand how these different components of COVID-19 immunity are related.
Number of cases
The reporting of coronavirus cases varies drastically around the world. Some regions are reporting that less than 1% of people have been infected, and others thatover half the populationhas had COVID-19. One study, which has been peer reviewed, estimated that only 35% of symptomatic caseshave been reportedin the US, and that the figure is even lower for some other countries.
When it comes to estimating true prevalence, scientists use just one of two main approaches. They either test a sample of people in a population for antibodies and directly report those numbers, or predict how the virus has affected a population using mathematical models. Such models have givenvery different estimates.
Research led by the University of Toronto in Canada, which hasn’t been peer reviewed yet, assessed blood test data from people across the world and discovered that the proportion who have had the virus varieswidely across countries.
We don’t know why. There could be real differences due to the age, health or spread of each population – or in policies to control virus transmission. But it is very likely it’s down to differences in the methodology, such as antibody tests (serological testing): different testshave different sensitivity.
Antibody studies suggestthat only 14% of peoplein the UK have had COVID-19, compared with 19% in Sweden and 3% in Yemen. But that excludes T-cells. If they provide a reliable guide to infection, the number may be much higher – potentially close to herd immunity in some regions – but this ishugely debated.
This article is republished fromThe ConversationbyManal Mohammed, Lecturer, Medical Microbiology,University of Westminsterunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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