Background Although vaccination against SARS-CoV-2 is considered the central strategy against the pandemic, uptake lags behind target rates. Method To explore whether this rate could be enhanced by a nudging strategy that exploits the status quo bias, we conducted a randomized controlled trial in northern Italy comparing vaccination acceptance among 2000 adults, ages 50 to 59 years, who were either invited to set an appointment (opt-in group) or assigned an individual appointment (opt-out group). Results Results indicate a difference of 3.2 percentage points, which represents a 32% relative increase in the vaccination rate for the opt-out group compared with the opt-in group. Conclusions A significant portion of those who remain unvaccinated may not hold strong beliefs against vaccination but rather tend to inaction and may therefore be nudged toward vaccination with a reduction of action required. Highlights Reluctant adults (50-59 years), who had not yet received vaccines against COVID-19, were sent letters announcing appointment availability In an RCT, the status quo option in the notices influenced the rate of vaccine acceptance Nudging via pre-scheduled appointments encouraged vaccine uptake more than invitations to schedule did Switching the default option yielded a 32% relative increase (13.1% vs. 9.9%) in vaccination

Repeated or prolonged exposure to an odorant without any positive or negative reinforcement produces experience-dependent plasticity, which results in habituation and latent inhibition. In the honeybee (), it has been demonstrated that, even if the absolute neural representation of an odor in the primary olfactory center, the antennal lobe (AL), is not changed by repeated presentations, its relative representation with respect to unfamiliar stimuli is modified. In particular, the representation of a stimulus composed of a 50:50 mixture of a familiar and a novel odorant becomes more similar to that of the novel stimulus after repeated stimulus preexposure. In a calcium-imaging study, we found that the same functional effect develops following prolonged odor exposure. By analyzing the brains of the animals subjected to this procedure, we found that such functional changes are accompanied by morphological changes in the AL (i.e., a decrease in volume in specific glomeruli). The AL glomeruli that exhibited structural plasticity also modified their functional responses to the three stimuli (familiar odor, novel odor, binary mixture). We suggest a model in which rebalancing inhibition within the AL glomeruli may be sufficient to elicit structural and functional correlates of experience-dependent plasticity.

Although the efficacies of vaccines against SARS-CoV-2, i.e., the virus that causes Covid-19, have been publicized and praised, and although they are assumed to encourage vaccine compliance, little is known about how well these figures are understood by the general public. Our study aims to fill this gap by investigating whether laypeople have an adequate grasp of what vaccine efficacy means and, if not, which misconceptions and consequences are the most common. To this end, we carried out three online behavioral experiments involving 1800 participants overall. The first, exploratory experiment, with a sample of 600 UK participants, allowed us to document by means of both an open-ended question and a multiple-choice question, a common misinterpretation of the efficacy of SARS-CoV-2 vaccines as the non-incidence rate among the vaccinated. We formally demonstrated that this error leads to a systematic overestimation of the probability of individuals who are vaccinated developing Covid-19. The second experiment confirmed the prevalence of this misinterpretation in a new sample of 600 UK and Italian participants, by means of a slightly different multiple-choice question that included more response options. Finally, in a third experiment, involving another 600 UK and Italian participants, we investigated the behavioral implications of the documented error and showed that it might undermine the general positive attitude toward vaccines as well as the intention to get vaccinated. On the whole, the results of this study reveal a general misunderstanding of vaccine efficacy that may have serious consequences for the perceived benefits of SARS-CoV-2 vaccines and, thus, the willingness to be vaccinated.

Although vaccination against SARS-CoV-2 is considered the central strategy against the pandemic, uptake lags behind target rates. To explore whether this rate could be enhanced by a nudging strategy that exploits the status quo bias, we conducted a randomized controlled study in northern Italy comparing vaccination acceptance among 2,000 adults aged 50-59 who were either invited to set an appointment (opt-in group) or assigned an individual appointment (opt-out group). Results indicate an increase in vaccination rate for the opt-out group compared to the opt-in group of 3.2 percentage points — a 32% relative increase. This suggests that a significant portion of those who remain unvaccinated may not hold strong beliefs against vaccination, but rather tend to inaction and may therefore be nudged toward vaccination with a reduction of action required.