Table 2.

Recommendations for increasing vaccination.

Intervention	Recommendation
Communications content Benefits of vaccination	Recommendation: Emphasising the benefits of vaccination to the self and others can be effective, but there are mixed findings. Studies on behaviour find that it is not more effective than informing individuals of where they can receive the vaccine [16]. There is evidence from studies on intention that it could be more effective with strongly hesitant groups, although it might not affect all demographic groups in the same way [20]. One possible explanation is that people already know the benefits and so there are other barriers to vaccination that are reducing uptake/ intentions. Indeed, more co-production work is likely to be beneficial in helping to identify the benefits relevant to specific groups. This use of co-production can also help identify how the benefits should be communicated with the target population (e.g., using appropriate content, communication sources or messengers). Outcome: Behaviour and intention Overall quality: Good/Fair (7 studies)
Communications content Effectiveness and safety	Recommendation: Reminders that emphasise vaccine effectiveness can increase vaccination uptake [17]. Evidence on intention suggests that communicating the effectiveness and safety of vaccines can have a positive effect, and could in fact be stronger for vaccine-hesitant individuals [25]. However, the evidence is mixed, with some research suggesting that it is no more effective than a control. The evidence also suggests that describing effectiveness and safety is more effective when there is high vaccine effectiveness and low risk of side-effects [29,30]. Outcome: Behaviour and intention Overall quality: Good (11 studies)
Communications content Vaccine development	Recommendation: It is unclear whether addressing the speed of development of vaccines and robustness of trials affects uptake since evidence is mixed [18]. However, one trial suggests that it could decrease hesitancy amongst vaccine-hesitant individuals [20]. Outcome: Intention Overall quality: Good (5 studies)
Communications content Social norms	Recommendation: Booking reminders telling others to ‘join the millions’ can be effective at increasing vaccine uptake but likely to be less effective than messages emphasising other aspects such as personal benefits [17] and safety [23]. Communicating that others intend to get vaccinated elicits mixed findings on intention, although could be effective in contexts where vaccination intentions are not clear [33], such as booster vaccinations. Social norms are a key facilitator for engaging in a range of behaviours and social norm interventions can be successful [54]. To be effective, social norms interventions need to be tailored to the target group, delivered by a member of the target group or a trusted individual and relevant to existing group norms [55]. Outcome: Behaviour and intention Overall quality: Good/Fair (5 studies)
Communications content Herd immunity	Recommendation: Highlighting how many need to be vaccinated to reach herd immunity could be effective, although this evidence is from one study [18]. Previous experimental evidence also suggests that communicating about herd immunity can increase vaccine uptake [34,35]. Outcome: Intention Overall quality: Good (1 study)
Communications presentation Personalisation	Recommendation: Vaccination invitations that mention that a vaccine has been made available to them can be effective in increasing uptake [16]. However, when sending a second reminder, personalisation is comparable to reminders [16]. Contrary to the field trial, an identical online experiment found that telling individuals a COVID-19 vaccine has been made available to them did not increase intention [16]. Outcome: Behaviour and intention Overall quality: Good (3 studies)
Communications presentation Framing	Recommendation: The effects of positive relative to negative framing are unclear from this limited evidence, suggesting that neither positive nor negative framing is more effective. A meta-analysis of framing effects in other vaccinations suggest that there is no effect of framing on vaccine intention [56], and therefore both positively and negatively framed information could be used. Outcome: Intention Overall quality: Good (3 studies)
Communications presentation Numerical format	Recommendation: The format in which effectiveness or lottery outcomes is communicated had no effect on vaccination intentions [31,36], although previous studies suggest frequencies are easier to understand than probabilities [57,58]. Outcome: Intention Overall quality: Good (2 studies)
Communications presentation Uncertainty	Recommendation: Communicating uncertainty about COVID-19 vaccines does not seem to decrease vaccination intention and may even be protective in terms of maintaining vaccination intention and trust in communicators if conflicting information arises over time [27,38]. This is consistent with guidance from the British Psychological Society, which recommends to communicate uncertainty and acknowledge change [59]. Outcome: Intention Overall quality: Good/Fair (3 studies)
Communications delivery Messenger	Recommendation: Match the messenger to the receiver in terms of characteristics, views, etc., as indicated by previous research [60,61]. Avoid controversial figures that might be divisive [26] and use trusted sources (e.g., NHS and GP). These trusted sources may vary between groups, meaning it is critically important to understand the views of target groups and their relationship to different sources. Outcome: Intention Overall quality: Good (4 studies)
Communications delivery Chatbot	Recommendation: Having an automated and instant chatbot providing vaccine information could increase vaccine uptake, although evidence is from one low-quality study with no control group and pre- and post-intervention vaccination intentions measured post-intervention [41]. Outcome: Intention Overall quality: Poor (1 study)
Communications delivery Video	Recommendation: Adding educational videos to reminders does not increase the effectiveness of the reminder in increasing vaccine uptake. There is mixed evidence regarding the use of videos in increasing vaccine intention. There are also difficulties with ensuring the videos reach a wide audience [43]. Outcome: Behaviour and intention Overall quality: Good/Fair (4 studies)
Communications delivery Reminders	Recommendation: Sending text message reminders increases vaccine uptake, as is the case in the interventions for the influenza vaccine [62]. Outcome: Behaviour and intention Overall quality: Good (4 studies)
Policy Mandatory vaccination	Recommendation: Mandating vaccination is unlikely to be an effective strategy to increase vaccination uptake, particularly amongst people who already have low intentions to receive the vaccine [44]. Mandating vaccinations could also lead to a reduction in uptake of future doses [63], resignation of health care staff [46] and exacerbating inequalities through increased risk of enforcement [64]. Outcome: Intention Overall quality: Fair/Good (2 studies)
Policy Vaccination proof	Recommendation: One study suggests that proof of vaccination (e.g., vaccination card) should be offered [29], although other literature suggests negative public attitudes towards requiring proof of vaccination for domestic activities and also a possible reduction in uptake, particularly amongst those who are vaccine hesitant [65,66]. Outcome: Intention Overall quality: Good (1 study)
Policy “Opt-out” vaccination	Recommendation: There is some evidence to suggest that automatically opting people into vaccine, such as pre-scheduling vaccine appointments, could be effective [47]. However, the manipulations within these experiments are not a true reflection of the design or impact of an opt-out vaccination system. Outcome: Intention Overall quality: Good (2 studies)
Policy Prioritising vaccination	Recommendation: Holding back or limiting vaccines could reduce uptake in individuals who are highly motivated to receive the vaccine [44]. Outcome: Intention Overall quality: Fair/Good (2 studies)
Policy Legal incentives	Recommendation: There is no evidence that offering easing of restrictions (i.e., face covering or testing) increases vaccine uptake, although this was only from one study in Germany [48]. Outcome: Intention Overall quality: Good (1 study)
Policy Monetary incentives	Recommendation: The limited evidence on monetary incentives for uptake in the US is mixed. There is some evidence to suggest offering monetary incentives is effective on intention, although small amounts could backfire [49]. Caution should therefore be applied when considering any monetary incentive. Offering a low incentive could reduce uptake amongst individuals with intrinsic, altruistic motivations to have the vaccine, whereas offering a large incentive could be deemed uneconomical and coercive [21,67]. Additionally, while a fixed sum of money or cash-equivalent vouchers could be effective, lotteries may not be effective [19]. Outcome: Behaviour and intention Overall quality: Good (10 studies)
Policy Cost	Recommendation: Requiring payment, including with a subsidy, for vaccination is likely to reduce uptake [30]. Outcome: Intention Overall quality: Good (1 study)
Vaccination Delivery Setting	Recommendation: Offer vaccinations in both community (e.g., pharmacy, local supermarket, or workplace) and medical settings (e.g., GP, hospital, and clinic) [29]. These settings should also be easily accessible by public transport [52,68]. Outcome: Intention Overall quality: Good/Fair (3 studies)
Vaccination Delivery Proximity	Recommendation: Limited evidence suggests that vaccine centres more than 30 min away could reduce uptake to vaccination [52]. Outcome: Intention Overall quality: Fair/Good (2 studies)
Vaccination Delivery Appointments	Recommendation: There is some evidence that appointments during the working day are preferred, although these factors are less influential than setting and proximity [39]. There is not enough evidence to determine the extent to which pre-booking appointments is preferable to walk-in centres, although it is possible that walk-in centres are more suitable for particular groups (e.g., traveller communities, homeless individuals) [69]. It is also important that booking systems work efficiently, as difficulties with the booking process, such as website crashes and telephone queues, are barriers to uptake [5]. Outcome: Intention Overall quality: Fair/Good (2 studies)
Vaccination Delivery Waiting time	Recommendation: Vaccine appointments not available within 30 days could discourage uptake, although this evidence is only from one study [28]. Individuals might be more willing to wait for an appointment which is nearer and which they can choose the time of [52]. Outcome: Intention Overall quality: Fair/Good (2 studies)