New research in rhesus monkeys suggests that contracting SARS-CoV-2, the virus that causes COVID-19, could protect against repeat infection.
Some recent reports have suggested that COVID-19 can reoccur in people after they have recovered from the disease.
However, the available scientific evidence has not confirmed that there is a risk of reinfection with SARS-Cov-2, the virus that causes COVID-19.
In a new study, which appears as a preprint on the scientific server bioRxiv, a team of researchers used rhesus macaques to explore the potential for COVID-19 reoccurrence.
The investigation, which has not yet been peer reviewed, involved reexposing the monkeys to SARS-CoV-2 after their symptoms had disappeared.
Linlin Bao, from the Beijing Key Laboratory for Animal Models of Emerging and Reemerging Infectious Diseases, is the first author of the paper.
Bao and colleagues infected four adult Chinese rhesus macaques with SARS-CoV-2 using tissue culture infectious doses.
They measured the monkeys’ body weight and temperature and took X-rays, sera samples, and nasal, throat, and anal swabs from the animals.
The monkeys each weighed 3–5 kilograms at the start of the study, and three of the four lost 200–400 grams after the initial infection.
The monkeys also briefly exhibited other clinical signs of the illness, such as a loss of appetite, increased respiration rate, and hunched posture.
The scientists measured the monkeys’ viral loads using respiratory and anal swabs. The viral loads reflected on nasal and pharyngeal swabs peaked 3 days after the initial infection, while those measured from anal swabs showed a similar peak, at 3 days. The viral loads then declined.
The euthanasia and necropsy of one of the monkeys revealed that the virus had made its way into the nose, pharynx, and lungs — as well as the gut, spinal cord, heart, skeletal muscle, and bladder.
The majority of the lesions occurred in the lungs, causing mild to moderate interstitial pneumonia.
To longitudinally track the characteristics after reinfection, the researchers measured the antibodies that the remaining three animals had naturally built up in response to the initial infection. They did so at days 14, 21, and 28 after the first infection.
X-rays revealed no abnormalities at day 28. Also, body weight and rectal temperature were stable, and “viral loads of nasopharyngeal and anal swabs were not detectable,” report the authors.
“Altogether, these data suggested that the three animals were considered as recovering from SARS-CoV-2 infection, similarly meeting the clinical discharge evaluation criteria,” they write.
Twenty-eight days after the initial infection, the scientists reinfected two of the three remaining monkeys, using the same viral dose. They kept the third monkey as a control subject and continually monitored its health, giving it no additional treatment.
Neither of the reexposed monkeys lost weight, while both showed a temporary spike in body temperature.
Importantly, “Viral loads in 96 nasopharyngeal and anal swabs tested negative after the reexposure of SARS-CoV-2,” report Bao and colleagues.
Euthanasia and necropsy of one of the reexposed monkeys 5 days after reinfection confirmed that there was “no viral replication in all tissues […] as well as no pathological damage and viral antigen in lung tissues.”
The scientists reached this conclusion after comparing necropsy results of the reinfected monkey to those of the monkey euthanized 1 week after the initial SARS-CoV-2 infection.
“Therefore, our results suggested that the monkeys with SARS-CoV-2 infection after recovery could not be reinfected with the same strain. Longitudinally, the monkey [that had] undergone single infection in this study did not appear [to show signs of] recurrence after the recovery, either,” write the authors.
Bao and the team conclude:
“Taken together, our results indicated that the primary SARS-CoV-2 infection could protect from subsequent exposures, which have […] vital implications for vaccine design [and disease prognosis].”
The researchers also highlight the key roles that specific antibodies play in the fight against the new coronavirus.
“From our current longitudinal study of monkeys,” they say, “the reinfection could not occur if the monkeys produced the neutralizing antibody at an early stage after the primary infection. Correspondingly, the convalescing patients won’t be contagious when they build up enough specific antibody to develop immunity to SARS-CoV-2.”
As for “the phenomenon [of] the discharged patients [who] tested positively, it may be attributed to the ‘false negative’ [reverse transcription polymerase chain reaction]test results before their discharge” or the patients not having fully recovered, despite meeting discharge criteria.
“Therefore, further refinement of the diagnostic techniques, antibody monitoring, and samples testing from the lower respiratory tract is essential for the cure of SARS-CoV-2 infection,” Bao and colleagues emphasize.
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