A “human challenge” study conducted in the United Kingdom has revealed some surprising findings regarding COVID, including evidence that many more people have innate immunity to COVID than is often assumed.

The study, published on Research Square, involved the participation of 36 young, healthy volunteers between the ages of 18 and 29, with no history of either prior COVID infection or vaccination against COVID. Each of them submitted to having SARS-CoV-2 “intranasally inoculated” (that is, dripped into their noses) and were then placed in quarantine, with constant monitoring including regular PCR and lateral flow testing.

After excluding two trial participants who tested positive for COVID after initial screening, the results were that 18 volunteers (53 percent) became infected. 16 did not.

The viral load in those who became infected rose steeply, peaking at around five days post-inoculation, between one and three days after symptoms developed. Viable virus was recoverable from the nose up to 10 days post-inoculation, however – meaning that the volunteers could still transmit the virus to others until that point.

Not one of the 34 people who completed the trial became seriously ill, nor were any adverse events recorded. 12 people developed transient issues with taste and smell.

The study’s results seemed to encourage use of the often-maligned lateral flow tests, with the authors noting that, “Lateral flow results were strongly associated with viable virus.” These tests picked up on viable virus on average 36 hours after a qPCR test did, but also tended to remain positive for up to three days after no more viable virus was present.

Another intriguing finding was that, “No quantitative correlation was noted between viral load and symptoms, with high viral loads even in asymptomatic infection … our data clearly show that SARS-CoV-2 viral shedding occurs at high levels irrespective of symptom severity, thus explaining the high transmissibility of this infection and emphasizing that symptom severity cannot be considered a surrogate for transmission risk in this disease.”

One of the contributors to the trial was Gilead Sciences Inc., which donated remdesivir to be used on trial participants. The first ten volunteers to have PCR-confirmed infection were given pre-emptive remdesivir, “with the aim of mitigating any unexpected risk of progression to more severe disease.”

“Following review … pre-emptive remdesivir was deemed unnecessary … Of the first 10 participants prospectively assigned to receive pre-emptive remdesivir on PCR-confirmed infection, 6 became infected,” the trial’s authors found.

They also noted that, “No apparent differences were seen in viral load … between remdesivir-treated and untreated infected individuals … With no significant differences between remdesivir-treated and untreated participants, infected individuals were therefore analyzed together.”