NIAC Recommendations on booster doses of COVID-19 vaccine for those aged 16-49 years

Access to and completion of a primary COVID-19 vaccine series in all countries is an essential prerequisite to control the global SARS-CoV-2 pandemic. Until worldwide control is achieved, all countries remain at risk.

In Ireland, COVID-19 vaccine uptake is very high, yet numbers of infection, hospitalisation, severe disease and death have increased. The rate of hospitalisation of unvaccinated people is substantially higher than in those who are fully vaccinated. However, as vaccination rates are so high, the proportion of those vaccinated who are admitted to hospital is increasing.

The high transmissibility of the Delta variant, waning of immunity following vaccination, increasing socialisation and the time lapse since vaccination have contributed to the surge in new infections and increased the risk of severe disease in those with underlying conditions. • The primary aim of the booster campaign is to protect against severe breakthrough infection.

Age and underlying conditions are the most important determinants of risk of severe breakthrough infection. • Pregnancy is a risk factor for severe illness and adverse outcomes related to COVID-19.

Booster vaccination is associated with a substantial reduction in the rate of severe illness in those aged 40 to 49 years and also a reduction in confirmed infection across the age groups.

As the effectiveness of the single dose COVID-19 vaccine Janssen vaccine is less robust than vaccines with a two dose schedule, offering an earlier booster vaccine may help to control the surge in case numbers in younger people.

Heterologous boosting following single dose COVID-19 vaccine Janssen is more immunogenic than homologous boosting and so is recommended.

Booster doses of mRNA vaccines have not shown any unexpected short term safety concerns. The risk of myocarditis or other rare adverse reaction following an mRNA booster dose has yet to be characterised and will be closely monitored. As a precaution, Comirnaty is the recommended booster vaccine for those aged 16 to 29 years.

NIAC continues to examine new evidence regarding COVID-19 vaccination of younger children and durability of protection of the primary vaccine series in other groups, e.g., the immunocompromised who received an additional dose and those aged 12 to 15 years.