The importance of sustained compliance with physical distancing during COVID-19 vaccination rollout

Mass vaccination campaigns against SARS-CoV-2 are ongoing in many countries with increasing vaccination coverage enabling relaxation of lockdowns. Vaccination rollout is frequently supplemented with advisory from public health authorities for continuation of physical distancing measures. Compliance with these measures is waning while more transmissible virus variants such as Alpha (B.1.1.7) and Delta (B.1.617.2) have emerged. In this work, we considered a population where the waning of compliance depends on vaccine coverage. We used a SARS-CoV-2 transmission model which captures the feedback between compliance, infection incidence, and vaccination coverage to investigate factors that contribute to the increase of the prevalence of infection during the initial stages of the vaccination rollout as compared to no vaccination scenario. We analysed how the vaccine uptake rate affects cumulative numbers of new infections three and six months after the start of vaccination. Our results suggest that the combination of fast waning compliance in non-vaccinated population, low compliance in vaccinated population and more transmissible virus variants may result in a higher cumulative number of new infections than in a situation without vaccination. These adverse effects can be alleviated if vaccinated individuals do not revert to pre-pandemic contact rates, and if non-vaccinated individuals remain compliant with physical distancing measures. Both require convincing, clear and appropriately targeted communication strategies by public health authorities. Significance StatementSARS-CoV-2 vaccination campaigns are in progress in many countries around the world. As the vaccination coverage increases, the compliance with physical distancing measures aimed at reducing virus transmission may decline. Using a socio-epidemiological model we identify factors that are the drivers of increased transmission when SARS-CoV-2 prevalence is higher than the projected prevalence without vaccination. To maximize the benefits of vaccination campaigns, compliance in vaccinated and non-vaccinated groups should be targeted prioritizing one group over the other depending on the vaccination rate, the efficacy of vaccine in blocking the infection, and the circulating variant.

Impact of self-imposed prevention measures and short-term government intervention on mitigating and delaying a COVID-19 epidemic

BackgroundThe coronavirus disease (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread to nearly every country in the world since it first emerged in China in December 2019. Many countries have implemented social distancing as a measure to flatten the curve of the ongoing epidemics. Evaluation of the impact of government-imposed social distancing and of other measures to control further spread of COVID-19 is urgent, especially because of the large societal and economic impact of the former. The aim of this study was to compare the effectiveness of self-imposed prevention measures and of short-term government-imposed social distancing in mitigating, delaying, or preventing a COVID-19 epidemic. Methods and FindingsWe developed a deterministic compartmental transmission model of SARS-CoV-2 in a population stratified by disease status (susceptible, exposed, infectious with mild or severe disease, diagnosed and recovered) and disease awareness status (aware and unaware) due to the spread of COVID-19. Self-imposed measures were assumed to be taken by disease-aware individuals and included handwashing, mask-wearing, and social distancing. Government-imposed social distancing reduced the contact rate of individuals irrespective of their disease or awareness status. The model was parameterized using current best estimates of key epidemiological parameters from COVID-19 clinical studies. The model outcomes included the peak number of diagnoses, attack rate, and time until the peak number of diagnoses. For fast awareness spread in the population, selfimposed measures can significantly reduce the attack rate, diminish and postpone the peak number of diagnoses. A large epidemic can be prevented if the efficacy of these measures exceeds 50%. For slow awareness spread, self-imposed measures reduce the peak number of diagnoses and attack rate but do not affect the timing of the peak. Early implementation of short-term government-imposed social distancing can only delay the peak (by at most 7 months for a 3-month intervention). The delay can be even longer and the height of the peak can be additionally reduced if this intervention is combined with self-imposed measures that are continued after government-imposed social distancing has been lifted. Our analyses do not account for stochasticity, demographics, heterogeneities in contact patterns or mixing, spatial effects, imperfect isolation of individuals with severe disease, and reinfection with COVID-19. ConclusionsOur results suggest that information dissemination about COVID-19, which causes individual adaption of handwashing, mask-wearing and social distancing can be an effective strategy to mitigate and delay the epidemic. Early-initiated short-term government-imposed social distancing can buy time for healthcare systems to prepare for an increasing COVID-19 burden. We stress the importance of disease awareness in controlling the ongoing epidemic and recommend that, in addition to policies on social distancing, governments and public health institutions mobilize people to adopt self-imposed measures with proven efficacy in order to successfully tackle COVID-19. Author summaryO_ST_ABSWhy was this study done?C_ST_ABSO_LIAs of May 2020, the coronavirus disease (COVID-19) caused by the novel coronavirus (SARS-CoV-2) has spread to nearly every country in the world since it first emerged in China in December 2019. C_LIO_LIConfronted with a COVID-19 epidemic, public health policymakers in different countries are seeking recommendations on how to delay and/or flatten its peak. C_LIO_LIEvaluation of the impact of social distancing mandated by the governments in many countries and of other prevention measures to control further spread of COVID-19 is urgent, especially because of the large societal and economic impact of the former. C_LI What did the researchers do and find?O_LIWe developed a transmission model to evaluate the impact of self-imposed measures (handwashing, mask-wearing, and social distancing) due to awareness of COVID-19 and of short-term government-imposed social distancing on the epidemic dynamics. C_LIO_LIWe showed that self-imposed measures can prevent a large epidemic if their efficacy exceeds 50%. C_LIO_LIShort-term government-imposed social distancing that is initiated early into the epidemic can buy time (at most 7 months for a 3-month intervention) for healthcare systems to prepare for an increasing COVID-19 burden. C_LIO_LIThe delay to the peak number of diagnoses can be even longer and the height of the peak can be additionally reduced if the same intervention is combined with self-imposed measures that are continued after lifting government-imposed social distancing. C_LI What do these findings mean?O_LIRaising awareness of self-imposed measures such as handwashing and mask-wearing is crucial in controlling the ongoing epidemic. C_LIO_LIShort-term early-initiated government-imposed social distancing combined with self-imposed measures provides essential time for increasing capacity of healthcare systems and can significantly mitigate the epidemic. C_LIO_LIIn addition to policies on social distancing, governments and public health institutions should continuously mobilize people to adopt self-imposed measures with proven efficacy in order to successfully tackle COVID-19. C_LI