NPHET has been advised that the period of presumptive immunity following infection with the SARS-CoV-2 virus should be extended from six to nine months.

The advice was published by the Health Information and Quality Authority (HIQA), which has carried out a review of international evidence relating to immunity. This review included 19 large cohort studies of reinfection, involving over 640,000 people who had previously been infected with the virus.

It was also informed by 13 studies on immune memory response, as well as expert opinion from the Covid-19 Expert Advisory Group.

“We have advised NPHET that the period of presumptive immunity should be extended from six to nine months post-infection. Across all the studies we examined, the risk of SARS-CoV-2 reinfection was consistently low, with no increase in infection risk over time.

“In addition, studies suggests that most people develop immune memory after a SARS-CoV-2 infection that lasts for at least nine months,” explained Dr Máirín Ryan, HIQA’s deputy CEO and director of health technology assessment.

Dr Ryan said that increasing the period of presumptive immunity from six to nine months “has widespread positive implications for people”.

“For example, a person who has Covid-19 in the last nine months would be exempt from serial testing. A change would also increase the number of under-50s who only need one dose of a COVID-19 vaccine to be considered fully vaccinated.

“It would also have implications for the implementation and roll-out of the proposed ‘green certificates’. It will be important that any policy changes and the evidence behind them are clearly communicated and consistently applied,” she commented.

However, HIQA added that the potential impact of new variants on natural immunity is “evolving rapidly” and must be kept under review.