Infection with the 2019 Novel Coronavirus, SARS-CoV-2 does not cause symptoms for up to two weeks, during which time individuals can transmit the coronavirus to others. Coupled with a lack of any immunity to SARS-CoV-2 in the population that has allowed SARS-CoV-2 to spread rapidly.
One strategy for dealing with the disease in the absence of a vaccine is to control the spread so as not to overwhelm healthcare systems and to develop community or herd immunity. This is where a large percentage of the population has been infected with SARS-CoV-2 and has recovered. In such a scenario, it would be difficult for the virus to take hold again, as if an individual has previously been infected, they would not be able to be infected again. While this approach could work, it is not without risk. There is little information about whether reinfection is possible and there have been some reports that patients who contracted COVID-19, the disease caused by SARS-CoV-19, have become ill again, which suggests the herd immunity approach may not be effective.
A team of researchers in China conducted a study to determine whether reinfection with SARS-CoV-2 is possible. The study was conducted on rhesus macaques, who were infected with SARS-CoV-2, recovered, and SARS-CoV-2 was reintroduced.
The study was conducted on 4 adult macaques who were confirmed to be infected based on viral replication in the nose, pharynx, and gut. The monkeys had also developed moderate interstitial pneumonia. One of the macaques was euthanized and autopsied 7 days after infection and was confirmed to have lesions in the lung and mild to moderate interstitial pneumonia. The remaining three monkeys recovered from the infection, based on two negative RT-PCR tests and the lack of any clinical symptoms of COVID-19.
29 days post-infection, two of the macaques were given the same dose of SARS-CoV-2 as was initially provided and the third macaque was used as a control and received no second exposure. Five days after the second SARS-CoV-2 dose, the researchers confirmed that in 96 nasopharyngeal and anal swabs, viral loads could not be detected. One of the macaques that had received the second dose was euthanized and autopsied and was found not to have contracted COVID-19 a second time, no viral replication was detected in any of the tissue samples, and no pathological tissue damage was detected.
The study suggests that reinfection with the same strain of SARS-CoV-2 is not possible. The researchers suggest that cases in China where patients appeared to be reinfected could be explained as a relapse rather than reinfection. Patients had sufficiently recovered to be discharged, but it is possible they had not actually fully recovered from the illness or that the RT-PCR tests had produced a false positive result.
You can read more about the small monkey study in the paper – Reinfection could not occur in SARS-CoV-2 infected rhesus macaques – which was recently published in the journal bioRxiv. DOI: 10.1101/2020.03.13.990226