A second booster dose against Covid-19 is likely to be offered in the autumn, the Government’s advisers on vaccination have said, but decisions on who should receive it have not yet been made.

Second boosters for people aged 65 and over are to be rolled out within weeks following a recommendation from the National Immunisation Advisory Committee (Niac). It said that these can be given at least six months after the first, though this interval can be reduced to four months "for operational reasons".

Minister for Health Stephen Donnelly has also accepted Niac's recommendation that a second booster, or fifth dose, be given to immunocompromised people aged 12 and older.

Hospital Report

A third booster will likely be needed for over-65s and the immunocomopromsied in the autumn, the committee advised, while provision of a second booster for the rest of the population is being kept under review.

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“A second booster dose will likely be required in autumn 2022. However, the additional cohorts to be vaccinated, and vaccine choice considering the likely predominant variant, epidemiology, transmissibility and seasonality and schedules remain to be determined,” it told the Minister in a letter.

Immunocompromised children aged five to 11 years should complete an extended primary course, ie three vaccine doses, Niac advised.

In each case, the booster administered should be the Pfizer vaccine, it is recommended, or Moderna for those aged 30 and over. Anyone who has been infected with Covid will have to wait six months before they can receive a second booster.

In recent months, Ireland has experienced a massive surge of Covid cases, driven by the spread of the Omicron/BA.2 variants. Most fully vaccinated and boosted people are considered to be well protected, but waning protection from vaccines has left older and immunocompromised people at risk.

The Health Protection Surveillance Centre on Wednesday reported 4,076 PCR-confirmed Covid-19 cases while a further 4,278 people registered a positive antigen test with the HSE on Tuesday.

There were 1,333 people with the disease in hospital on Wednesday morning, a reduction of 27 in 24 hours. The total included 58 patients in intensive care, an increase of four.

Health officials say one-third of people in hospital with coronavirus are unvaccinated or incompletely vaccinated. Niac says primary vaccination has a “limited short-term impact” on infection with the Delta variant, with protection declining after 12-20 weeks .

“The decline with the Omicron variant is even more rapid. Protection against hospitalisation and severe illness is more durable.”

How effective are boosters?

A first booster dose can massively increase antibody levels but these then fall by up to half after 90 days. Against Omicron, UK studies show the effectiveness of a first booster dose against symptomatic disease dropped to 25-40 per cent after 15 weeks.

Even a fourth dose of Pfizer vaccine offers only short-lived protection against infection, with the protection offered almost gone after eight weeks, a new Israeli study published this week indicated. Protection against severe illness waned more slowly.

Niac has highlighted the importance of children and adolescents aged 12-15 years and older completing their primary course of vaccines by receiving a booster dose, while those aged five to 11 years should complete a primary course of two doses.

More than 700,000 people have received two primary vaccine shots but not a booster shot.

Niac reiterated its previous recommendation that all pregnant women should be offered the vaccine.

Mr Donnelly said the second booster would be rolled out quickly. Assuming many people in the 65+ age group received their booster last November or December, they would be looking at having a second booster jab in May or June.

Niac also notes the presence in the UK of three new “recombinant” variants, including XE, a mix of BA.1 and BA.2, which is growing almost 10 per cent faster than BA.2. “As yet it is too soon to determine their impact on disease severity or vaccine effectiveness,” it comments.