This brief review of evidence aims to investigate whether there are further vaccination strategies and/or eligibility groups that could be incorporated to reduce the spread of influenza and to reduce severe disease, influenza-associated hospitalisations and deaths in Aotearoa New Zealand (NZ).
The key areas that are reviewed are given below:
• respiratory infection burden in NZ communities
• directly protecting individuals – children and targeting groups at highest risk
• indirect protection and reduction of community spread – population vaccination, improving coverage and ring protection.
Individual vaccination continues to play an important role in controlling influenza and reducing the risk for severe outcomes, particularly for higher risk groups, which also should include people with morbid obesity. However, some groups, particularly elderly with a high degree of frailty (reduced function and health), are less likely to have a strong immune response to traditional influenza vaccines. Newer influenza vaccine types have the potential to improve vaccine effectiveness in these high-risk groups.
Vaccination strategies that focus on broader population-wide approaches can help to control the spread of the infection and thus provide further supportive protection to those most at risk from influenza and less able to respond individually to the current vaccines. The optimal approach is a broad, population-wide vaccination programme for everyone from the age of 6 months, with maternal vaccination to help to protect infants too young to receive the vaccine. To provide direct and indirect protection against severe influenza outcomes, ideally all Māori and Pacific people should be recommended to be vaccinated against influenza from 6 months of age. Consideration needs to be given as to how and where vaccine is accessed; targeted approaches are likely to be required in areas of high deprivation.
The greatest benefit of school-based vaccination is to the children themselves, by reducing the risk of severe respiratory illness and reducing school absenteeism. There is some limited evidence that this strategy protects other groups but varies with different settings. It is likely that there would be additional benefit on transmission reduction in the community since children are known to be significant spreaders of influenza. The potential for an age shift in infection dynamics due to lower natural immunity from circulating virus in school-leavers and young adults who previously received influenza vaccination in school may affect the ability of this strategy to reduce impact on the elderly.
Vaccination of all younger children (age 2–4 years) and infants (6–23 months) is likely to provide greatest direct benefit to these age groups. The current funding for those with high-risk medical conditions is not reaching all young children that need protection from influenza. Some children only become eligible for funded influenza vaccine after they have been hospitalised with influenza or other respiratory infections. Evidence indicates that targeting high-risk preschool children alone does not reduce hospitalisations significantly. Improvements in influenza vaccine uptake in pregnancy also provides short-term but important protection for the youngest infants who cannot be vaccinated against influenza.
• Influenza vaccination is more effective in children aged over 3 years than in older adult age groups.
• It takes fewer doses of vaccine in children to protect against influenza than adults – the number needed to be vaccinated to prevent one case of influenza is predicted to be five.
• Vaccination attenuates disease severity.
• By encompassing all children into the vaccination programme, a greater level of protection will be provided to children at higher risk of severe outcomes than targeted vaccination of children within defined risk groups.
• Routine population influenza vaccination of children reduces antibiotic prescribing, school absenteeism and general practice visits.
• Individual vaccination plays a key role in reducing severe influenza outcomes.
• Some immunocompromised individuals, such as elderly adults, do not respond as well to standard influenza vaccines as healthy adults and children, and are likely to benefit from recombinant, adjuvanted or high dose vaccines. Individuals who are morbidly obese should also be considered among this group.
• By reducing the spread of influenza, broad population-based approaches can help to provide additional protection to the most at risk.
• All Māori and Pacific peoples from age 6 months would benefit from funded influenza vaccine.
• School-based vaccination provides the greatest protection directly to the children themselves.
• An additional benefit of school-based vaccination is to help reduce the spread of influenza to the wider community.
• Vaccination of workers in the health and education sectors reduces the impact influenza on these services through staff absenteeism as well directly protecting these staff. Patients and young children are also indirectly protected from being infected.
• Vaccination of all young children aged 6 months to 4 years is required to directly reduce the burden of influenza in these age groups. Vaccination in pregnancy provides passive protection to infants too young to receive influenza vaccine.
• Consideration is required as to how and where vaccine is accessed; targeted approaches are likely to be require in areas of high deprivation.