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COVID reinfections make herd-immunity non-viable.

  • Revelations of a possible reinfection case in Melbourne has cast doubts over herd immunity and the longevity of vaccine protection against COVID-19, immunology experts say. "I'm not surprised," said Associate Professor Nathan Bartlett, who works at the Hunter Medical Research Institute and has been studying respiratory diseases for 20 years. Professor Bartlett said the nature of coronaviruses was they tended to be localised in the upper respiratory system and did not offer strong ongoing immunity. "There have been studies that have looked longitudinally at reinfections with human coronaviruses. There is clear data on this, and you can become reinfected with coronaviruses, throughout your life. These coronaviruses go round and round and round, year after year. If we had herd immunity you wouldn't get continued recycling of infections and circulating viruses. The virus would die out and that's the whole point of herd immunity." This was supported by Associate Professor Paul Griffin who has been leading two vaccine trials. "The implications of this [reinfection case] include adding further weight to the argument that a herd immunity strategy based on allowing the infection to spread is fundamentally flawed and should not be considered as an option," said Professor Griffin, the director of infectious diseases at Mater Health Services in Brisbane. 21/Oct/20

Some of the other discussions about reinfections:

  • - What reinfections mean for COVID-19

  • One of the key questions in predicting the course of the COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is how well and how long the immune responses protect the host from reinfection. For some viruses, the first infection can provide lifelong immunity; for seasonal coronaviruses, protective immunity is short-lived.

  • In The Lancet Infectious Diseases, Richard L Tillett and colleagues describe the first confirmed case of SARS-CoV-2 reinfection in the USA. A 25-year-old man from the US state of Nevada, who had no known immune disorders, had PCR-confirmed SARS-CoV-2 infection in April, 2020 (cycle threshold [Ct] value 35·24; specimen A). He recovered in quarantine, testing negative by RT-PCR at two consecutive timepoints thereafter. However, 48 days after the initial test, the patient tested positive again by RT-PCR (Ct value 35·31; specimen B).


  • Researchers in Hong Kong recently reported the first confirmed case of reinfection with the COVID-19 virus. The man was first infected in March, then declared to be recovered after two negative coronavirus tests. Four and a half months later, he tested positive for coronavirus on a saliva screening test administered at the Hong Kong airport upon his return from a trip to Europe.

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