A year on: what we now know about COVID-19

COVID-19 is not 'like flu'

In the early days of the pandemic some reports likened COVID-19 to seasonal flu - but while both COVID and flu are respiratory viruses that can cause anything from mild to life-threatening illness, we now know that there are some important differences.

Although COVID-19 has a longer 'incubation period' than flu (around 5-6 days) meaning it doesn't spread as quickly, the 'reproductive number' is slightly higher (between 2.4 and 3.1 as opposed to 2 in flu), meaning it's more infectious.

When it comes to influenza, children drive much of the transmission. But with COVID-19, children seem to be less affected than adults - in fact, a recent study suggested that children tend to catch the illness from adults rather than the other way around.

Sadly, the mortality (death) rate appears to be significantly higher in COVID-19: even now, there are few data sets which provide a comprehensive estimate, but it is probably in the region of 0.8% overall for confirmed cases, very heavily skewed towards older people. Death rates for patients severe enough to need hospital admission is about three times higher for COVID-19 than for influenza.

Airborne particles can be infectious

Like many viruses, COVID-19 is transmitted through liquid particles, released when an infected person coughs or sneezes. At the start of the pandemic it was thought only larger droplets - perhaps picked up on surfaces or from direct contact - could cause infection.

We now know that COVID-19 can also be transmitted through tiny aerosol particles, meaning spending time in a poorly-ventilated space with someone who has COVID-19 - even if you socially distance - may lead to infection. Masks help to reduce the risk of infection if you come into contact with an infected person, but only offer limited protection, especially if they are standard (rather than PPE-grade) face coverings.

Scientists also now know that some people can carry the virus but show no symptoms at all. It is estimated that 1 in 5 people may not show symptoms but may still be infectious, meaning it's possible to catch COVID-19 from someone who appears to be completely healthy.

COVID-19 has many symptoms

In March 2020, not all of the symptoms of COVID-19 infection were known. Once testing was initially available, patients developing fever or a new, continuous cough were advised that they might be carrying COVID-19. Now you can book a free PCR test to find out if you have COVID-19 if you have either of these or have lost or experienced a change to your sense of smell or taste. Asymptomatic testing is also available in some areas.

With many more people experiencing infection and reporting symptoms, we now know to look out for a range of other symptoms, including:

• Sore throat

• Headache

• Joint or muscle pain

• Diarrhoea

• Nausea or vomiting

• Dizziness and chills

• Skin rash

• Nasal congestion

• Conjunctivitis

COVID-19 affects some people more

When the virus first emerged, it was unclear as to who would be the most susceptible to the disease, although doctors (rightly) assumed those with underlying health conditions - such as cancer, diabetes or high blood pressure - and the elderly were at most risk of serious disease.

However, we now also know that the risks of COVID-19 infection to children are tiny compared to those for adults (especially older adults), although in rare cases they may develop a severe inflammatory syndrome weeks after infection.

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Long COVID

Most people with COVID-19 infection (SARS CoV-2 infection) feel better within a few days or weeks and recover completely within 12 weeks of the infection. However, some people have ongoing symptoms that remain for weeks, months, or longer, which is usually called "long COVID". For some, these long-term effects of COVID-19 can be debilitating. These effects can be very different from person to person, and it seems likely that there are different 'types' of long COVID, or different syndromes, which might behave in different ways.

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COVID-19 can lead to 'long COVID'

At the start of the pandemic, we already knew that the disease presented differently in different individuals - but COVID-19 was seen as a disease that would have a duration of a few weeks at most.

However, there is now a bank of evidence suggesting that some individuals go on to develop a condition referred to as 'long COVID' where symptoms can include weakness, fatigue, shortness of breath and other problems. As this is a relatively new condition it is not known how long these symptoms may last.

There is an increasing amount of support available for people with long COVID, including specialist sites with access to a range of specialists to support the management of ongoing symptoms. In February a £2.2 million research project was announced to improve understanding and treatment of the condition.

Treatment for COVID-19 has evolved

When COVID-19 first appeared in early 2020, there were no treatments established for this disease other than pain relief medication to relieve symptoms, administering oxygen to those who needed it, and ventilator treatment if oxygen by mask was not sufficient.

However, the situation has now improved and trials have indicated that dexamethasone, a corticosteroid, can reduce the rate of death in those with severe complications by up to one third.

"Dexamethasone can only be used in severe or critical cases," explains Dr Jeff Foster, GP. "In terms of severity this would include acute respiratory distress syndrome, sepsis or septic shock, or an oxygen saturation of less than 90%."

Although scientists are yet to develop a targeted medication for COVID-19, treatment of the disease has evolved alongside our understanding - leading to better patient outcomes.

"There have been some changes in the way the Intensive Treatment Unit (ITU) manages the most severe patients. They are often carefully monitored for signs of secondary pneumonia, sepsis and acute kidney injury, for example," says Foster.

"One of the major changes has been the understanding that COVID-19 causes a hypercoagulable state (a condition where your blood is more likely to clot) in some people and can cause blood clots. Therefore this is monitored more carefully and blood thinners given to prevent this complication which can occur for several weeks after."

Doctors have now discovered that the position patients lie in can also make a significant difference to outcomes - so-called 'proning' (with patients lying on their fronts) has become more widely used.

Vaccines and the future of COVID-19

Vaccines have been developed rapidly for this disease and there are now several vaccines approved for use in the UK, which have proved to be up to 97% effective in preventing COVID-19 infection. Their safety has been carefully assessed throughout and results have been extremely reassuring.

However, although things are starting to look more positive, it's impossible to know the number of people who need to be vaccinated in order to reach 'herd immunity' which is when enough of the population carry antibodies to cause the disease to die out.

"This is because it depends on how infectious the virus is or how easily the virus spreads and mutates. For example, measles needs around a 95% population immunity for it to be effective, whereas polio only needs 80%," Foster explains. "However, it is worth noting that COVID-19 will probably not be completely wiped out for many years. This is because it spreads and can mutate (change) easily."

What may happen is that COVID-19 will become 'endemic' - meaning it exists all the time at a low level, "with low numbers of people being infected and some dying every year - a bit like flu now. It is even quite possible that as variants become more understood we might have a yearly COVID-19 booster in a similar way we do for flu variants."

It is likely that COVID-19 will remain part of our lives for some time to come. In order to ensure the effect on daily life is minimised, it is important that people are vaccinated to protect themselves and others, and to drive overall infection rates down.