Free and perfectly safe but only partially effective vaccines can harm everyone

VACCINE HESITANCY, PASSPORTS, AND THE DEMAND FOR VACCINATION

Vaccine hesitancy is modeled as an endogenous decision within a behavioral epidemiological model with endogenous agent activity. It is shown that policy interventions that directly target costs associated with vaccine adoption may counter vaccine hesitancy whereas those that manipulate the utility of unvaccinated agents will either lead to the same or lower rates of vaccine adoption. This latter effect arises with vaccine passports whose effects are mitigated in equilibrium by reductions in viral/disease prevalence that themselves reduce the demand for vaccination.

Benefit of COVID-19 vaccination accounting for potential risk compensation

People receiving COVID-19 vaccines may subsequently markedly increase their previously suppressed exposure risk. A simple model can evaluate the benefit of vaccination to the vaccinated (index) person and others exposed to that person; and calculate the amount of risk compensation required to eliminate all the benefits or to halve the benefit. As shown, 2.5-fold increase in exposure will eliminate the benefit of a vaccine of moderate efficacy (E = 0.6) unless the probability of infection in the population of interest is very high. With very high vaccine efficacy (E = 0.95), substantial benefit is maintained except in situations where there is a very low probability of infection in the population. If the vaccine efficacy decreases to 0.8, the benefit gets eroded easily with modest risk compensation. Risk compensation may markedly affect the benefit of COVID-19 vaccination, especially if vaccine efficacy in real-life or specific high-risk populations (e.g., nursing home residents) is not very high.

An imperfect test for a virus can Be worse than No test at all

This note studies the effect of the availability of a test for a virus on the public health of a population. It is shown by example that the existence of a freely available and moderately informative test for a virus may lower society's welfare in comparison to the case where no test exists or access to the test is restricted. In this setting, any test provided to any subset of agents who would find it optimal not to isolate absent the test improves welfare.

The dangers of performative scientism as the alternative to anti-scientific policymaking: A critical, preliminary assessment of South Africa's Covid-19 response and its consequences

At the onset of the Covid-19 pandemic South Africa was praised for decisive political leadership based on scientific advice and the strictness of the measures it imposed to limit domestic spread of the virus. This paper critically examines the South African response through two conceptual frameworks. The first frames an optimal policy response as a solution to an intertemporal welfare-optimisation problem. The need for governments to balance epidemiological considerations and public health measures with the negative consequences of non-pharmaceutical interventions to limit transmission is particularly acute in developing countries. The second considers the use of scientific evidence and expertise through the lens of scientism - undue deference to science. The South African government erred towards drastic action in the face of predictions by some scientific advisors of a catastrophe, but initially without a clear, public long-term plan. Its lockdown has caused serious economic and societal harm across a range of measures. But these costs have not been matched by proportional benefits in health system preparedness or, based on evidence three months into the epidemic, a definitive improvement in expected long-term epidemic outcomes. This failure, and the questionably confident basis for the original lockdown decision, has been obscured by the government's performative scientism - a public performance of deference to science - even in the absence of transparent decision-making. One consequence was a slower correction of strategy than merited by evidence of limited benefits and high costs of the lockdown. Another was an unwillingness to admit and explain errors after the fact. The latter, combined with the convincingness of the initial performance undermined the behavioural dimension of policy - leading to beliefs among citizens that confounded efforts by the state to adapt its policy stance through reopening schools, reducing the stringency of clinical guidelines and resuming various economic activities while nevertheless observing basic social distancing precautions.