COVID-19 vaccine protects against reinfection significantly: study

Individuals who have already been infected with SARS-CoV-2, the virus that causes COVID-19, benefit from a vaccine as well, with 60% to 94% protection against reinfection depending on the variant, according to a research. These findings are reported in the open-access journal PLOS Medicine by a new study conducted by Katrine Finderup Nielsen from Statens Serum Institut in Denmark. During the last epidemic, vaccination was one of the most effective techniques for limiting the spread of COVID-19. People who have been infected with the virus are known to have long-lasting natural immunity, but Finderup Nielsen and her colleagues wanted to determine if these people would still benefit from the vaccination.

The researchers examined infection and vaccination data from Danish national registries, which included all Danes who tested positive for the virus or were vaccinated between January 2020 and January 2022. More than 200,000 persons tested positive for SARS-CoV-2 during the Alpha, Delta, and Omicron waves were included in the data collection. According to their findings, for persons who had previously been infected, immunisation provided up to 71% protection against reinfection during the Alpha phase, 94% protection during the Delta period, and 60% protection during the Omicron period, with protection lasting up to nine months.

These data suggest that vaccination protected persons against SARS-CoV-2 in addition to natural immunity during all three waves of variations. The authors caution out that the present trial was too short to assess if the vaccination protects against serious outcomes like mortality and hospitalisation, and that larger follow-up studies would be needed to answer this question. In terms of public health, these insights on vaccine efficacy can assist decision makers plan the scheduling and execution of vaccination efforts to maximise their effectiveness.

Finderup Nielsen adds, “In our study we find a significant vaccine effectiveness against SARS-CoV-2 reinfection, and this shows the importance of vaccination also for those who might be protected by natural immunity.”