This phenomenon is assumed to be one of several reasons for the variability in disease severity seen with COVID-19. They also explain differences in vaccine efficacy seen in different age groups.

For the current study, researchers recruited individuals with no prior exposure to SARS-CoV-2, testing them at regular intervals to establish whether they had contracted the infection.

Out of a total of nearly 800 participants who were recruited from mid-2020 onwards, 17 persons tested positive. The researchers studied the affected individuals’ immune systems in detail.

Their analyses showed that the immune response against SARS-CoV-2 also included the mobilization of immune cells which had been generated in response to endemic common cold viruses.

They also showed that the quality of the immune response against SARS-CoV-2 was linked to the quantity of cross-reactive cells which had been present in the body prior to infection. These cells were particularly effective at recognizing a certain area of the spike protein.

These findings furthermore confirmed that the immunity-enhancing effects of cross-reactive immune cells also occur following vaccination with COVID-19 vaccine. Just like natural infection, the vaccine also prompts the body to produce the SARS-CoV-2 spike protein and present it to the immune system.

In second part of the study, researchers analyzed immune cells in approximately 570 healthy individuals. They were able to show that cross-reactive immunity declines in older adults.

This decline in cross-reactive immunity is caused by normal, age-related changes. They also suggest that a third (or booster) dose would be able to compensate for this weaker immune response, ensuring that members of this high-risk group have adequate immunity.

Source: Medindia