Why do people without underlying health conditions get seriously ill from covid-19?
Some people get seriously ill from covid-19 without any known risk factors. Genetic make-up is likely to play a role – we have long known that having a parent who died young from an infectious disease puts you at a sixfold greater risk of doing so yourself. The genes that make a difference are probably involved in the immune system.
Are you protected if you have been infected by a different coronavirus?
There are at least four other kinds of coronavirus that cause coughs and colds, but we don’t know if having encountered one of these puts you in a worse or better position. Often, if your immune system makes antibodies against one microbe, it gets a head start for fighting a related one later on.
But this doesn’t always apply. There is evidence that encountering a virus can sometimes lead to worse symptoms in subsequent infections involving the same virus or a similar one.
“It isn’t safe to assume you can’t catch or spread the virus if you have already recovered from it”
This seems to happen when the body doesn’t make very effective antibodies. Worryingly, there are hints from animal studies that these can be triggered by the SARS coronavirus – leading to concerns that prior coronavirus infections may be harmful, not protective.
Do people who survive covid-19 become immune to the virus?
The consensus is that recovered people will have some level of protection for at least a few months. We don’t yet know how much protection or how long it will last. People who recover from coronavirus infections do so because their immune systems kick in and eliminate the virus, so they are immune at their point of recovery. But a 1990 study of other human coronaviruses found that people can be reinfected with the same virus a year later – although the second time around they didn’t get symptoms and were infectious for a shorter period.
So, it isn’t safe to assume that you can’t catch or spread the coronavirus if you have already recovered from it, and we may find that vaccines cannot provide permanent protection as a result.
Can vitamin D supplements improve our immune response to covid-19?
There is a link between levels of vitamin D – which seems to play a role in our immune system – and some other viral infections, like the flu and other respiratory tract infections, but it isn’t clear cut.
We get most of our vitamin D from exposure to sunlight, and many people are deficient in vitamin D, especially those in countries that get less sunlight and those with dark skin tones.
However, when Susan Lanham- New at the University of Surrey, UK, and her colleagues compared vitamin D levels in people who tested positive for the coronavirus with those in people who didn’t, they found no difference.
A handful of randomised, controlled clinical trials are under way. We don’t know if vitamin D will be helpful for fighting off covid-19, but it is best to make sure you aren’t vitamin D deficient.
Will social distancing measures have an effect on other infections, like flu and measles?
They already are having an effect. In Australia, the flu season should be building up around now, but flu cases there in April were in the low hundreds, compared with nearly 19,000 at the same time last year. Lots of hand washing and keeping at a distance is bad
news for any respiratory virus, including coughs, colds, measles and chicken pox. When social distancing measures ease, though, rates of other infections are likely to return to their normal levels.
What is the risk of catching the virus from fresh produce?
We don’t know for sure, but it is likely to be low. The virus has been found to persist on surfaces for days, or even weeks given the right environment, yet it is unlikely to remain infectious for this long. “[The risk is] almost certainly low, but you should still wash your fruit and veg when you get home, especially if it is likely to have been on display,” says Paul Hunter at the University of East Anglia, UK.
Flu vaccines help protect those most vulnerable or likely to catch influenza
Properly cooking food will kill off viruses. But if you plan to eat your fruit and veg raw, it is worth washing them. The advice from the World Health Organization (WHO) is to “wash them the same way you would in any other circumstance”, which means washing your hands before you handle them, and washing produce with water before you eat it.
“Properly cooking food will kill off viruses. The WHO recommends washing raw fruit and veg”
Are toilets and sewage systems an infection risk?
It is possible, because people with covid-19 shed the virus in their faeces. When Yuguo Li at the University of Hong Kong and his colleagues analysed surface and air samples taken from a hospital treating people with covid-19, the team found the most virus in samples taken from toilets.
In 2003, the SARS virus is thought to have spread through a housing block through plumbing and ventilation systems, but overall, the risk of getting the virus from toilets or sewage is low, according to the WHO.
What is more likely – a successful vaccine, or an effective drug?
We are likely to see several drugs approved for treating covid-19 before any vaccine becomes available, but they won’t be miracle cures.
We will almost certainly find drugs that have statistically significant effects, but these effects are likely to be modest. For instance, a drug called remdesivir has received emergency use approval in the US based on initial results suggesting that it shortens recovery time, but it doesn’t seem to reduce the number of deaths.
A real game-changer would be a drug that helps people with severe covid-19 recover. Instead of targeting the virus, such a drug would need to help reverse the severe inflammatory response – called a cytokine storm – that it triggers in some people. No such drug has been developed yet.
Human trials of several vaccines have already begun. There is no guarantee that these efforts will succeed, but many vaccine researchers are optimistic.
Could antibodies from recovered patients be used as a treatment for covid-19?
This approach is already being tested in about 20 randomised trials. The idea behind convalescent plasma or serum therapy, as it is known, is that it can take weeks for our bodies to produce enough antibodies to overcome a new virus. Injecting severely ill people with antibodies made by others who have recently recovered could help fight the virus in the meantime.
A 14 May review of the handful of small, non-randomised studies published so far concluded that it was uncertain if this approach is effective against the coronavirus. What’s more, one of the 32 people treated in these studies developed anaphylactic shock.
Even if serum therapy is effective, it is hard to scale up. Several firms are starting to make pure antibodies in factories, an approach that is likely to be safer.
You can take pills to cut your risk of catching HIV – could something similar be made against the coronavirus?
For a few years, pre-exposure prophylaxis (PrEP) has been enabling higher-risk people to cut their risk of contracting HIV.
There is currently an intense research effort to develop antiviral drugs that could treat covid-19 by stopping the coronavirus from multiplying. If successful, these antivirals could potentially be used in a prevention strategy similar to HIV PrEP.
However, to take a drug for preventive purposes, rather than as a treatment, we need to be as sure as possible that it is safe, and that is likely to take many years. Because most people don’t get severely ill with covid-19, it is likely that such a preventive drug would be given only to those thought to be particularly vulnerable or at high risk of exposure.
Will countries that successfully contain the virus refuse visitors from countries that don’t?
It isn’t clear how travel bans might slow the spread of disease. Only a handful of studies have estimated how such bans might have affected the spread of Ebola and SARS. These suggest Flu vaccines help protect those most vulnerable or likely to catch influenza that, while bans might delay the arrival of a virus, they don’t stop the spread in the long term.
Travel bans have been implemented in several countries, and it is plausible that countries will consider longer-term measures, or wider use of testing and quarantine for any new arrivals. But there will always be some travel between countries, says Hunter. “In a global society, you can’t ban all movement in and out of a country,” he says. “You’d starve to death.”
Will covid-19 always be with us or can it be eradicated?
Countries such as China, South Korea and New Zealand are showing that it probably is possible to eliminate the virus. This requires a lot of effort though. China is trying to test 11 million people in 10 days to prevent a second wave of infection in Wuhan.
“It probably is possible to eliminate the virus – but it requires resources and political will”
Many countries lack the resources or political will to do this. The US and the UK, for example, are already looking at easing coronavirus restrictions despite having large outbreaks and insufficient systems for testing and contact tracing. If approaches like this continue, the virus will become widespread and come to be seen as less of a threat, but only after many more deaths.
A vaccine could be the answer to wiping the virus out, but as the WHO’s Michael Ryan noted at a press conference on 13 May, we have failed to eradicate diseases for which we do have vaccines, such as measles. “The virus may never go away,” he said.
Reprint from New Scientist
HEALTH 20 May 2020
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