The number of people under 50 who may only need one dose of a Covid-19 vaccine may increase as a result of new evidence on presumed immunity after infection with the disease, the Health Information and Quality Authority (HIQA) has said.

It will also have implications for the proposed EU Digital Green Certificate.

HIQA also said that people who had Covid-19 in the last months should be exempt from serial testing.

Today, the authority published its report which has found that the duration of immunity following Covid-19 infection should be extended from six to nine months post-infection, and it has issued this advice to the National Public Health Emergency Team (NPHET).

Dr Máirín Ryan, deputy HIQA CEO and Director of Health Technology Assessment, said that most people develop immune memory that lasts for at least nine months.

She said that increasing the period of presumptive immunity from six to nine months has "widespread positive implications" for people.

"It will be important that any policy changes and the evidence behind them are clearly communicated and consistently applied," she added.

HIQA also said that the potential impact of new variants on natural immunity is evolving rapidly and needs to be kept under review.

The HIQA report follows a review of international evidence, including 19 large studies of re-infection of over 640,000 previously infected people.

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Speaking on RTÉ's News at One, Dr Ryan also said people who have had Covid-19 within the last nine months will be entitled to Digital Covid Certificates, and also will not have to undergo serial testing that happens in high risk settings.

"Anyone who's had Covid-19 in the previous nine months will automatically be entitled to a green certificate. It also is relevant in the context of serial testing," she said.

"So somebody who's recovered from the Covid-19 in the last nine will no longer be due to have serial testing, for example the regulated testing that happens in high-risk settings like meat processing plants."

Dr Ryan said the finding is particularly relevant when considered in the context of the fact that two thirds of the population who were infected with Covid-19 in Ireland contracted the virus since the beginning of this year.

The presumed immunity of these people can now be extended.

"This is quite relevant when we think that two thirds of the people who are infected with SARS CoV2, who acquired Covid-19, in Ireland have acquired since the beginning of this year.

"So those people who acquired it in January, their presumed immunity would have been expiring around the beginning of July, whereas now it will persist out for another three months."