The world’s first study in which volunteers were intentionally infected with Covid-19 found that people were infected after just two days, much less than scientists had predicted.
Sponsored by the UK Government The “human challenge” challenge found that levels of Sars-Cov-2 virus in the nose and throat peaked after five days, although participants remained infectious for an average of nine days and a maximum of 12 days after upon contact.
The researchers say their results support guidance that people should isolate for 10 days after they first feel symptoms of Covid or test positive.
The study took place in a special unit at the Royal Free Hospital in London. Eighteen out of 34 volunteers aged 18 to 29 became infected after administering a low dose of the initial Sars-Cov-2 strain via intranasal droplets.
No one had severe symptoms, although 13 people temporarily lost their sense of smell. Only one volunteer still had that symptom after six months.
Christopher Chiu, professor of infectious diseases at Imperial College London, who was the lead investigator of the trial, said: “Our study reveals some very interesting clinical insights, especially regarding the timing of the study. The virus has a short incubation period, and the amount of virus emitted from the nose is very high.
The test is a partnership between Imperial, Royal Free and hVivo, a human challenge research firm, of London-listed Open Orphan.
Participants began to develop symptoms within two days of receiving a nasal dose of the virus (10 micrograms). High levels of viral infection appear first in the throat and almost immediately later in the nose.
Levels peak after five days, at which point the nose is the primary site of infection. The findings highlight the importance of wearing a mask that covers both the mouth and nose, the researchers say.
Lateral flow tests have also been shown to be a good indicator of whether someone is infectious.
“We found that the lateral flow test correlates very well with the presence of infectious virus,” said Chiu. “Although for the first day or two they may be less sensitive, but if you use them correctly and repeatedly, and act on them if they are positive, this can have a big impact. in preventing the spread of the virus.”
His Royal colleague Professor Wendy Barclay said that, although 10 days of self-isolation is a good guide when there is no testing, the results support a cut down to 5 days followed by results. negative lateral flow test on two consecutive days.
The research was initially launched to help test an experimental vaccine, before Pfizer and BioNTech announced they had developed an effective injectable drug in late 2020.
Jonathan Van-Tam, England’s deputy chief medical officer, said they had provided more “important data” on the virus, and could use more challenge trials in humans to accelerate development. of vaccines and other antiretroviral drugs.
Andrew Catchpole, principal scientist at hVivo, said that although the study focused on the original Sars-Cov-2 strain and there are differences in transmissibility between it and other variants, “the factors are similar each other will be responsible for protecting against it, meaning the findings are still valid for variants like Delta or Omicron.”
Open Orphan says it is developing a strain of Delta virus with Imperial that can be used in future tests.
