Even if infected with COVID-19, 'Infectiousness Drops Significantly After 7 Days'

COVID-19 Primate Infection Model Experiment Results
Rapid Proliferation for 2 Days Followed by Decline
No Infectious Virus Detected from Day 7
Observed Vasculitis, Lymphocytopenia, and Interstitial Pneumonia

[Asia Economy Reporter Junho Hwang] It has been revealed through experiments on primate infection models that when infected with the novel coronavirus disease (COVID-19), the virus rapidly proliferates in the throat and lungs for two days, then decreases, and from the seventh day onward, its infectivity significantly drops. Vascular endotheliitis, a symptom of COVID-19 that was not well known, was commonly observed, and the disappearance of immune cells was also identified. These research findings are expected to greatly aid the future development of COVID-19 treatments and vaccines.

COVID-19 Infection Experiments on Primates Most Similar to Humans

On the 5th, Minister of Science and ICT Kiyoung Choi held a review meeting at the Korea Chamber of Commerce and Industry with COVID-19 researchers and animal experiment experts to examine the results of primate experiments.

Primates are animals genetically, anatomically, and immunologically very similar to humans. Because of this similarity, COVID-19 infection experiments using primates can provide highly valuable clues for the development of treatments and vaccines.

The Korea Research Institute of Bioscience and Biotechnology (KRIBB) began research in February to develop a primate infection model for COVID-19 treatment and vaccine development. Following China, the Netherlands, and the United States, it became the fourth in the world to develop such an infection model. The primate infection models used were two species of macaque monkeys (rhesus and crab-eating macaques). Subsequently, KRIBB inoculated COVID-19 into the primate infection models and examined the results.

Rapid Proliferation for Two Days... Infectious Virus Disappears from Day 7

COVID-19 rapidly proliferated for two days. After that, it gradually decreased, and from the seventh day, no infectious virus was detected.

Ryu Choong-min, head of the Infectious Disease Research Center at KRIBB, explained, "The phenomenon where no infectious virus is detected indicates that the virus’s infectivity has significantly dropped."

This also explains why molecular diagnostic tests (PCR) for COVID-19 can yield positive results while actual infection symptoms do not appear, resulting in false-positive diagnoses.

COVID-19 mostly proliferated in the upper respiratory tract (throat) and lung areas. During the experiment, the researchers inoculated COVID-19 through various routes where the virus is detected in humans, but clear proliferation was observed mainly in the respiratory tract.

Interstitial Pneumonia, Vasculitis, and Lymphocytopenia Observed

Vascular endotheliitis was commonly found in primates infected with COVID-19. The research team announced that they were the first in the world to confirm that COVID-19 causes inflammation of blood vessels and that this inflammation persists in the vessels even three days after infection.

Vascular endotheliitis is a disease that progresses to vasculitis, causing inflammation in the blood vessel walls, which leads to tissue damage such as narrowing or widening of the inner walls and bleeding. Director Ryu said, "Since vasculitis was commonly found in primates, we checked symptoms in confirmed patients and found that vasculitis was also observed in some patients."

The reduction of immune cells was also confirmed through this study. Lymphocytopenia, a condition where immune cells disappear broadly from the blood during the most active acute phase of the virus, was observed. KRIBB explained, "While the immune system in healthy individuals may activate and overcome COVID-19, this finding clarifies why immunocompromised patients or those with weakened immunity can face fatal situations."

The researchers also found interstitial pneumonia in primates, similar to humans. Although the severity of the lesions was not life-threatening, it showed moderate to severe symptoms beyond mild cases.

Most Primates Overcome COVID-19

The research team stated that most of the primate infection models overcame COVID-19 in this experiment. This is similar to human patients who recover from COVID-19 infection. However, whether the normal function of organs exposed to the virus is maintained remains a task to be examined in the future.

They also expect that reinfection or immune deficiency, similar to AIDS, in human patients who appear to overcome COVID-19 can be verified through primate infection models.

The research results were published as a cover article on June 3 (local time) in the Journal of the Infectious Diseases Society of America.

Minister Kiyoung Choi said, "The characteristics of the COVID-19 virus revealed using the primate infection model can provide important clues not only for identifying the causes of the unique symptoms and transmission patterns in COVID-19 patients but also for the development of treatments and vaccines."

He added, "The government will use the primate model, the fourth in the world to be secured, to verify the efficacy of candidate substances discovered by the 'Government-wide Support Committee for COVID-19 Treatment and Vaccine Development' and ensure that the verification results are quickly connected to clinical trials."