Navigating post-vaccine COVID-19 futures in the health and economic context

The economic costs of the pandemic have been high, and vaccines offer an exit strategy. In The Lancet Infectious Diseases, Frank Sandmann and colleagues model a range of future scenarios in the UK depending on vaccine efficacy, duration of protection, and use of physical distancing, and the respective health and economic impacts of these scenarios.¹ This study is the first full economic evaluation of different vaccination scenarios compared with an unmitigated epidemic, with varying degrees of physical distancing. It shows that lockdowns and physical distancing reduce economic losses, which refutes the false perceived dichotomy of protecting the economy at the expense of pandemic control. The authors also show the health and economic benefits of mass vaccination of adults in the UK.

In the best-case vaccination scenario, with 95% vaccine efficacy and 3-year protection against infection, requirements for increased physical distancing (ie, reducing contacts by 90% outside of the home) are minimal. In the worst-case scenario, with 50% vaccine efficacy and 45-week protection against disease, but not infection, recurrent epidemics will occur with ongoing need for increased physical distancing.¹ Although the study considers hypothetical scenarios of higher and lower vaccine efficacy, there is already wide variation in efficacy of available vaccines. Phase 3 trials show 63–95% efficacy against symptomatic infection, with the highest efficacy shown for mRNA vaccines.2, 3, 4 The ChAdOx1 nCoV-19 vaccine trial is the only one to date presenting data on prevention of asymptomatic infection, and efficacy is much lower for this endpoint.²

Economic losses are substantially less when high-efficacy vaccines are used, whereas lower-efficacy vaccines with short duration of protection will provide marginal benefits compared with no vaccination.¹ The best-case vaccination scenario will result in substantial economic gains compared with no vaccination, but the worst-case scenario might not, depending on vaccine costs and the wider societal cost of ongoing lockdowns. Duration of vaccine-induced immunity is also an important factor that affects the economic value of vaccination, but vaccine-induced protection could be extended by boosters. Therefore, the most influential factor is the efficacy of the vaccines being used, and thus vaccine choices matter enormously for economic recovery. Governments should grasp the importance of procuring the highest-efficacy vaccines as the route to achieving a best-case economic scenario. In countries that rely on lower-efficacy vaccines, be it by choice or lack thereof, the long-term health and economic burden might be similar to if no vaccine were used, if a very high threshold (eg, 100 cases per 100 000 population) were used to trigger physical distancing measures.

The study shows that if natural immunity is long lasting, the economic value of immunisation decreases.¹ However, the mRNA vaccines result in higher neutralising antibody titres than in convalescent sera.⁵ Furthermore, in Manaus, Brazil, where 76% of the population had been infected by October, 2020—higher than the hypothesised herd immunity threshold—a large second wave has since occurred.⁶ In addition, variants of concern show evidence of vaccine escape.⁷ The South African Government paused the planned rollout of the ChAdOx1 nCoV-19 vaccine because the efficacy against the B1.351 variant was found to be 10·4%.⁸ All vaccines can be matched to emergent variants, but we are likely to face a situation of regular revision of vaccine antigens, which will add to future cost.

The variants of concern also pose a challenge because they are more contagious. If they become dominant, this will require higher vaccine coverage and higher-efficacy vaccines, making a compelling case for use of the highest-efficacy vaccines at the outset to avoid an intermediate or worst-case scenario and to reduce selective pressure for emergence of more variants.

Sandmann and colleagues' study assumes high vaccine uptake in all scenarios, but in many countries, vaccine supply might be limited, so targeted vaccine use could be needed initially. Vaccine hesitancy and inequity in distribution and access might also contribute to a patchy uptake. The most common approach for use of limited supply is age-based or risk-based targeting, but ring vaccination should also be considered. Many vaccines are effective as post-exposure prophylaxis (PEP), including those for measles, hepatitis A, and smallpox, and the long incubation period of SARS-CoV-2 means vaccines might work as PEP.⁹ Sandmann and colleagues show that if the start of the vaccination programme is delayed, outcomes are worse. A slow trickle in uptake will also lead to worse health and economic outcomes than rapid uptake.⁹ Israel achieved rapid, early mass vaccination in less than 2 months with an mRNA vaccine, and showed a measurable impact of vaccination on pandemic dynamics.¹⁰

The health and economic burden of living with COVID-19 in the intermediate and worst-case scenarios creates a double disadvantage of high disease burden and high economic cost of ongoing physical distancing measures. While we do not yet know if herd immunity is possible, only the use of high-efficacy vaccines (at least 80–90% against all infection) can possibly achieve it, especially if children can also be vaccinated.⁹ Sandmann and colleagues' research provides a rational pathway to aiming for a best-case health and economic scenario.