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A recent study has suggested that people who have recovered from COVID-19 develop only a short-lived immunity to SARS-CoV-2. (Image: Tatiana Buzmakova/Shutterstock)

SARS-CoV-2 infection, reinfection and immunity: What researchers say

By Iveta Ramonaite, Dental Tribune International
January 28, 2021

HARLOW, UK: Now that many questions regarding COVID-19, including its symptoms, risks and recovery time, have been answered, researchers are faced with a new dilemma: SARS-CoV-2 reinfection and immunity. Although unusual, it is evident that reinfections do occur, and in a recent study, researchers explored whether individuals who have recovered from COVID-19 are protected from future infection. The findings suggested that past infection may provide natural immunity and that the said immunity is effective for approximately half a year after the initial infection.

In what is considered to be the largest study of SARS-CoV-2 reinfection, researchers in the UK recruited 6,614 healthcare workers. They received SARS-CoV-2 polymerase chain reaction and antibody testing every two to four weeks and completed questionnaires on their symptoms and exposures every two weeks. The researchers found that approximately 83% of the participants who had a prior history of SARS-CoV-2 infection showed a lower risk of becoming reinfected with the virus and that their immunity lasted for at least five months after primary infection. However, the researchers do not exclude the possibility that those previously infected may still be able to carry and transmit the virus.

“This study has given us the clearest picture to date of the nature of antibody protection against COVID-19 but it is critical people do not misunderstand these early findings,” said senior author Dr Susan Hopkins, senior medical adviser at Public Health England, in a statement. “We now know that most of those who have had the virus, and developed antibodies, are protected from reinfection, but this is not total and we do not yet know how long protection lasts. Crucially, we believe people may still be able to pass the virus on,” she continued.

“It appears that reinfection usually, but not always, gives milder symptoms, presumably as a result of the immune response to the original infection”
— Dr Jonathan P. Stoye, Francis Crick Institute

Commenting on the study, Dr Jonathan P. Stoye, a virologist at the Francis Crick Institute in London, told Dental Tribune International (DTI): “We know from the SIREN [SARS-CoV-2 Immunity and Reinfection Evaluation] study of UK health workers that infection results in a certain degree of protection, but that reinfection can occur in some cases. It appears that reinfection usually, but not always, gives milder symptoms, presumably as a result of the immune response to the original infection.”

Vaccination vs natural immunity

While healthcare workers, including dental professionals, are patiently waiting to receive their vaccinations in order to help take the pressure off healthcare systems, important questions arise: is the immunity provided by vaccination superior to natural immunity? And if so, how long does immunity from a vaccine last? As there is currently little data on reinfection, researchers are still unable to provide clear-cut answers.

Discussing the effectiveness of natural immunity compared with vaccination-conferred immunity, Dr Akiko Iwasaki, Waldemar Von Zedtwitz Professor of Immunobiology and Molecular, Cellular and Developmental Biology at Yale School of Medicine in the US, told DTI: “Natural immunity appears to be pretty good at providing protection against reinfection. However, the mRNA vaccines have superb efficacy (~95%) against SARS-CoV-2. We don’t know how long the immunity lasts after infection vs vaccination, but the vaccination has the advantage of a booster shot to maintain high levels of protective immunity.”

Similarly, Stoye is hopeful that vaccines will offer immunity that is long-lasting: “We know that the immune response to natural infection can vary in extent. It is to be hoped that vaccination will more consistently give higher levels of immunity,” he said.

The first person to have become reinfected with SARS-CoV-2 is said to be a 33-year-old man living in Hong Kong. According to CNN, his second infection was confirmed on 15 August, upon his return from a trip to Spain. The patient was reinfected 4.5 months after his initial infection, which suggests that his immune response was rather short-lived. Since then, scientists have recorded 31 confirmed cases of SARS-CoV-2 reinfection worldwide, two of which resulted in death, according to an article published in The BMJ.

The cohort study, titled “Do antibody positive healthcare workers have lower SARS-CoV-2 infection rates than antibody negative healthcare workers? Large multi-centre prospective cohort study (the SIREN study), England: June to November 2020”, was published online on 15 January 2021 on medRxiv.

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