While the risk of breakthrough infection increases over time, the latest evidence suggests that Covid-19 vaccination continues to provide strong protection against severe disease and mortality for at least six months, the Health Information and Quality Authority (HIQA) has said.

It has published three reviews on the duration of immunity following vaccination in order to inform the work of the National Immunisation Advisory Committee (NIAC).

As part of this, HIQA reviewed international evidence from over 50 studies in order to assess the duration of protective immunity following vaccination in the general population and in two specific subgroups – healthcare workers and people with underlying conditions.

The reviews found that while the risk of breakthrough infection increased over time, overall, the evidence suggests that vaccination continues to provide strong protection against severe disease and mortality for at least six months post-vaccination.

The studies that looked specifically at healthcare workers showed similar high levels of protection against severe disease as those seen in the general population.

However, some studies suggested that there is waning protection particularly for older adults and in those with immune-compromising conditions.

“Despite the good protection afforded by vaccination, national and international data indicate a higher risk of severe disease outcomes in older individuals and in those with underlying conditions. Given this and the potential lower vaccine response for these populations, any additional reduction in protection would be of concern,” commented Dr Mark O’Loughlin of HIQA.

The reviews acknowledged that public health measures, infection prevalence and vaccination rollout have varied across countries and over time. Additionally, new variants of concern have emerged. As a result, it is difficult to determine if reductions in protection are due to waning immunity, differences in exposure, increased transmissibility and/or vaccine escape from new variants, or a mixture of all these factors.

“There is some uncertainty regarding protection after six months, especially in relation to new variants of concern and changing public health measures. We would encourage anyone who has been offered a booster dose to avail of it and give themselves the best protection possible,” Dr O’Loughlin added.

The HIQA reviews can be viewed here.