A new study shows that symptoms of COVID-19 appear just two days after exposure to the virus – much earlier than previously thought. As part of the Human Challenge, 36 healthy young people were deliberately infected with the coronavirus in a London hospital. The study found that it took two days for symptoms to appear, rather than five to six days according to the previous WHO estimate.
A study has shown that symptoms of coronavirus appear just two days after exposure to the virus – much earlier than previously thought, writes the Daily Mail.
As part of the Human Challenge, 36 healthy young people were intentionally infected with COVID-19 at a London hospital. The study found that symptoms appear on average in just two days, compared to previous World Health Organization (WHO) estimates of five to six days.
The government-supported study led by Imperial College London involved volunteers aged 18 to 29 who had never had COVID before. They were kept in a quarantine unit for at least 14 days at the Royal Free Hospital and deliberately injected with a very small dose of coronavirus in the form of nasal drops.
Only 53% of this group developed COVID-19. The authors said that the fact that nearly half of the volunteers avoided the disease could help explain why some people managed to avoid infection throughout the pandemic.
Experts have found that the coronavirus infection first appears in the throat, and then the symptoms peak around the fifth day, when the level of the virus in the nose is significantly higher.
Sixteen people in the group developed mild to moderate cold symptoms, including a stuffy or runny nose, sneezing and a sore throat, but no one became seriously ill.
Lead author Professor Chris Chiu says: “Shortly after infection, within two days, people begin to show the virus, first in the throat and then in the nose, where the virus developed very rapidly.” Among those patients who were asymptomatic, some still had very low detection rates of the virus, suggesting they may have an immune process suppressing the infection, the scientist said.
The study also found that sidestream tests are very effective in detecting the virus.
Study co-author Dr. Andrew Catchpole says the findings also apply to the Delta and Omicron variants of the coronavirus, although the study used the “original” variant of COVID-19. He said: “This shows that the virus can multiply very quickly. We haven’t tested with Delta or Omicron so all we can do is guess what can be seen. What we know from what we’ve seen in the field is that these viruses transmit very quickly and multiply very quickly, so we expect there will be a lot of data being transferred between them.” The study also found that high levels of viable (infectious) virus can still be detected in lab tests for up to nine days, and in some cases up to 12 days.
Peak levels of the virus were significantly higher in the nose than in the throat, suggesting a potentially greater risk of virus shedding from the nose than from the mouth.
The researchers say this highlights the need for people to properly use face masks that cover not only the mouth but also the nose.
“From a scientific point of view, these studies are of real benefit, because the time of exposure to the virus is always exactly known, so things like the interval between exposure and the virus shedding profile can be accurately described,” comments Professor Sir Jonathan Van Tam, Deputy Chief Medical Officer. England. “This important research has provided additional key data about COVID-19 and how it spreads, which is invaluable for learning more about this new virus so we can fine-tune our response. The research carried out may be important in the future to accelerate the development of “next generation” vaccines against COVID-19, as well as antiviral drugs. This data highlights how useful lateral flow tests can be in identifying contagious individuals, as well as the importance of wearing masks in crowded indoor spaces.”