The Effectiveness of Interventions for Increasing COVID-19 Vaccine Uptake: A Systematic Review

"...examines the cutting-edge and evolving literature concerning COVID-19 vaccination to highlight possible interventions that could be used to increase uptake of the COVID-19 vaccine."

Vaccine hesitancy is complex, with a plethora of underlying concerns. Some of these concerns pertain to vaccinations more broadly, while others are specific to the context of COVID-19. In addition to barriers relating to knowledge and beliefs, there are also environmental barriers, such as vaccine shortages. Barriers are also not universal; therefore, it is important to understand the extent to which interventions are effective amongst specific groups. The aim of this systematic review is to identify and evaluate the effectiveness of interventions to increase COVID-19 vaccine uptake.

The researchers searched a range of databases from March 2020 to July 2021 for studies that reported primary quantitative or qualitative research on interventions to increase COVID-19 vaccine uptake. In total, 39 studies across 33 papers met the inclusion criteria. A total of 28 were assessed as good quality, per National Heart, Lung and Blood Institute (NHLBI) risk of bias assessment.

The studies included interventions relating to communication content, communication delivery, communication presentation, policy, or vaccination delivery, with 7 measuring vaccination uptake and 32 measuring vaccination intention. Interventions were tested with a range of methods - most commonly online randomised controlled trials (RCTs) (20 studies) but also including field RCTs, online experiments (e.g., discrete choice experiments), and quasi-experimental and cross-sectional studies. The included studies were tested in a range of countries.

A narrative synthesis was conducted, which highlighted that there is reasonable evidence from studies investigating real behaviour suggesting that personalising communications and sending booking reminders via text message increases vaccine uptake. For example, a field RCT (pre-print) found that text messages communicating the personal or social benefit of COVID-19 vaccination increased uptake.

Findings on vaccination intention are mixed but suggest that communicating uncertainty about the vaccine does not decrease intention. An online RCT found that a news story communicating the personal health risks of not getting vaccinated, and another communicating the collective public health consequences of not getting vaccinated, increased vaccination intention. Studies found that making vaccination mandatory could have a negative impact on intention.

Based on the review, the researchers provide a series of recommendations in Table 2 in the paper, which also specifies whether interventions have been tested on real behaviour and/or intentions and provides average risk of bias assessment for each type of intervention. In brief:

• Communication content
  • Benefits of vaccination - Emphasising the benefits of vaccination to the self and others can be effective, though there are mixed findings. Studies find that this type of communication is not more effective than informing individuals where they can receive the vaccine. 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. More co-production work is likely to be beneficial in helping to identify not only the benefits relevant to specific groups but also the way the benefits should be communicated (e.g., using which messengers).
  • Effectiveness and safety - Reminders that emphasise vaccine effectiveness can increase vaccination uptake. Evidence on intention suggests that communicating the effectiveness and safety of vaccines can have a positive effect, though the evidence is mixed. The evidence also suggests that describing effectiveness and safety is more effective when there is high vaccine effectiveness and low risk of side effects.
  • Vaccine development - One trial suggests that addressing the speed of development of vaccines and robustness of trials could decrease hesitancy amongst vaccine-hesitant individuals, but the evidence is mixed.
  • Social norms - Booking reminders telling others to "join the millions" can be effective at increasing vaccine uptake but is likely to be less effective than messages emphasising other aspects, such as personal benefits and safety. Communicating that others intend to get vaccinated elicits mixed findings on intention, although it could be effective in contexts where vaccination intentions are not clear (e.g., with booster vaccinations). To be effective, social norms interventions need to be tailored to the intended group, delivered by a member of that group or a trusted individual, and be relevant to existing group norms.
  • Herd immunity - Highlighting how many people need to be vaccinated to reach herd immunity could increase vaccine uptake.
• Communication presentation
  • Personalisation - Vaccination invitations that mention that a vaccine has been made available to them can be effective in increasing uptake. However, the evidence is mixed.
  • Framing - A meta-analysis of framing effects in other vaccinations suggest that there is no effect of framing on vaccine intention, and therefore both positively and negatively framed information could be used.
  • Numerical format - The format in which effectiveness or lottery outcomes is communicated had no effect on vaccination intentions, although previous studies suggest that frequencies are easier to understand than probabilities.
  • Uncertainty - 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.
• Communication delivery
  • Messenger - Evidence supports matching the messenger to the receiver in terms of characteristics, views, etc., avoiding controversial figures that might be divisive, and using trusted sources (which vary, meaning that is important to understand the views of particular intended groups and their relationship to different sources).
  • Chatbot - Having an automated and instant chatbot providing vaccine information could increase vaccine uptake, although evidence is from one low-quality study.
  • Video - 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.
  • Reminders - Sending text message reminders increases vaccine uptake, as is the case in interventions for the influenza vaccine.
• Policy
  • Mandatory vaccination - This strategy is unlikely to be effective in increasing vaccination uptake, particularly amongst people who already have low intentions to receive the vaccine. Mandating vaccinations could also lead to a reduction in uptake of future doses, resignation of healthcare staff, and exacerbation of inequalities through increased risk of enforcement.
  • Vaccination proof - One study suggests that proof of vaccination (e.g., vaccination card) should be offered, 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.
  • "Opt-out" vaccination - There is some evidence to suggest that automatically opting people into vaccination, such as pre-scheduling vaccine appointments, could be effective. However, the manipulations within these experiments, which measure intention, are not a true reflection of the design or impact of an opt-out vaccination system.
  • Prioritising vaccination - Holding back or limiting vaccines could reduce uptake (intention) in individuals who are highly motivated to receive the vaccine.
  • Legal incentives - There is no evidence that offering easing of restrictions (e.g., face coverings or testing) increases vaccine uptake, although this finding was only from one study that measured intention.
  • Monetary incentives - The limited evidence on monetary incentives for uptake is mixed. There is some evidence to suggest that offering monetary incentives is effective on intention, although small amounts could backfire.
  • Cost - Requiring payment, including with a subsidy, for vaccination is likely to reduce uptake.
• Vaccination delivery
  • Setting - Research supports offering vaccinations in both community (e.g., pharmacy, local supermarket, or workplace) and medical settings (e.g., hospital or clinic). These settings should also be easily accessible by public transport.
  • Proximity - Limited evidence suggests that vaccine centres more than 30 minutes away could reduce uptake to vaccination.
  • Appointments - There is some evidence that appointments during the workday are preferred, although these factors are less influential than setting and proximity. Walk-in centres may be more suitable for particular groups (e.g., traveller communities, homeless individuals). Difficulties with the booking process, such as website crashes and telephone queues, are barriers to uptake.
  • Waiting time - Vaccine appointments not available within 30 days could discourage uptake, although this evidence is only from one study. Individuals might be more willing to wait for an appointment that is closer to them whose time they can choose.

The findings of this review may have implications for local and national health authorities with regard to the way they communicate with the public regarding their eligibility for vaccination. The heterogeneity of results, particularly amongst vaccine-hesitant people compared to vaccine accepters, highlights the importance of understanding an intervention's intended audience and the barriers that may deter them. The researchers call for further study of effective and acceptable interventions for encouraging vaccine uptake amongst these groups in particular.

Future research should also take into consideration the barriers that are unique to booster doses of the COVID-19 vaccine, such as previous experience with side effects, lack of awareness of the necessity of booster doses, and the feeling of being misled regarding the benefits of the primary vaccine doses.

In addition, although much of the research covered in this review used experimental designs, very few measured real behavioural outcomes; therefore, it is important that future research builds upon the current evidence to identify under which circumstances interventions are effective at increasing vaccine uptake.