Covid-19 vaccine studies carried out
There is some uncertainty about Covid-19 vaccine protection after six months, especially in relation to new variants such as Omicron according to the health service watchdog that advises NPHET.
The Health Information and Quality Authority (HIQA) has published the three reviews on the duration of immunity following COVID-19 vaccination to inform the work of the National Immunisation Advisory Committee (NIAC).
HIQA reviewed international evidence in order to assess the duration of protective immunity following COVID-19 vaccination in the general population and in specific subgroups.
It says the initial review examined the duration of protective immunity following COVID-19 vaccination in all populations aged 12 years and older. The first update focused on healthcare workers, while the second update focused on individuals with underlying conditions.
The reviews identified over 50 studies. While the risk of breakthrough infection increased over time, overall the evidence suggests that COVID-19 vaccination continues to provide strong protection against severe disease and mortality for at least six months post-vaccination.
However, some studies suggest that there is waning protection particularly for older adults and in those with immunocompromising conditions. Studies that looked specifically at healthcare workers showed similar high levels of protection against severe disease to that seen in the general population.
Dr Mark O’Loughlin, a Public Health Fellow in HIQA, said: “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.”
"Public health measures, infection prevalence and vaccination rollout have varied across countries and over time. Additionally, new variants of concern have emerged. 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," he said.
"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 said.
HIQA says three reviews will inform the work of the National Immunisation Advisory Committee (NIAC).
It says the duration of protective immunity from COVID-19 following vaccination is an important consideration for Ireland’s vaccination strategy, particularly for groups who may be at a higher risk of exposure (such as healthcare workers), those who have a less than optimal response to vaccination, or for whom there is evidence that immunity may wane over time.
It says the three reviews were conducted in sequence, with the second and third reports based on updated literature reviews. The three reviews did not examine the impact of booster doses.
As of December 2021, following conditional marketing authorisation from the European Medicines Agency, four COVID-19 vaccines are licensed and distributed for use in Ireland. These are ChAdOx1 (AstraZeneca), Ad26.COV2.S (Janssen), mRNA-1273 (Moderna) and BNT162b2 (Pfizer/BioNTech).
HIQA says it conducts evidence synthesis to inform national strategic decision-making. These evidence syntheses are conducted at the request of NPHET and related groups tasked with the national COVID-19 response.
The topics HIQA researches are outlined and prioritised by NPHET to ensure rapid access to the best available evidence relevant to the pandemic.
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