A study by researchers from Newcastle University suggests that working-age adults who have previously been infected with SARS-CoV-2 may be protected from reinfection for at least six months. This study was published in the Journal of Infection.
Research has started to suggest some level of protection from reinfection with SARS-CoV-2, and there is evidence of protection for up to 12 months following infection with other seasonal coronaviruses. However, we still do not know what level of protection is bestowed or how long this protection might last. This is important as we do not know if the many people infected with SARS-CoV-2 in the first wave are likely to be at risk of reinfection in the near future. Healthcare workers are also a useful cohort to follow due to their relatively high risk of infection and the fact that many have received symptomatic testing from early on in the pandemic.
The researchers identified a cohort of 11,175 healthcare workers who had received routine symptomatic testing within Newcastle-upon-Tyne Hospitals during the first wave of the pandemic in the UK (10 March – 6 July). This included 1,038 healthcare workers with evidence of prior infection, either through a positive PCR test (polymerase chain reaction, used to detect small amounts of the virus’ genetic material) or by testing positive for IgG antibodies, an indication of recent infection with SARS-CoV-2. They also included a control group of 10,137 healthcare workers who had no evidence of prior infection during the same time period.
Following up several months later, the researchers looked at which healthcare workers then experienced symptoms akin to COVID-19 during the second wave in the UK (7 July – 20 November). These individuals were then tested for SARS-CoV-2 using a PCR test. From this group, they found that none of the healthcare workers who tested positive in the first wave tested positive for COVID-19. This suggested that their previous infection provided some protection from being infected at a later date. This was despite 12.3% of the group presenting for testing with symptoms, however the authors note this does not account for anyone infected but not showing any symptoms (asymptomatic infection). In contrast, 2.9% of the control group, not known to have had a prior infection, did test positive during the second wave, with 20.9% presenting for testing in this time.
There were no significant differences in age or gender between groups, however those testing positive in the first wave were more likely to be from BAME backgrounds or to score lower on the index of multiple deprivation.
Importantly, this study does not study the immune response that may have caused the protective effect seen, and does not tell us about protection against asymptomatic infection. Future work would need to look at this in more detail as well as how long lasting this protective effect might be and how these results might apply to those in other at risk populations, such as the elderly, those with other health issues, or the immunocompromised.