by Dr. Nell Thomas
Vaccines are making their way through our community.
More of us are feeling that cloak of protection start to form around us after getting the shot. It sure does take the edge off the constant feeling of vulnerability and the vigilance we have all been burdened with. But until vaccination coverage helps us to reach herd immunity, nonpharmaceutical interventions remain the primary means of preventing virus spread. In some countries, such as Taiwan, for example, population behaviour has been the key to controlling spread of the virus.
Border control and compulsory mask wearing on public transit was imposed at the outset in Taiwan. Therefore, this island nation (population 23.6 million) had no locally-acquired cases of COVID-19 for the 253 days between April and December 2020. As of February 28, 2021, there had been 955 confirmed cases of COVID-19 in Taiwan, with only 77 (8.1 per cent) locally acquired.
Adherence to social distancing and face masking, plus quarantining and contact tracing. These are the techniques that have made Taiwan a country with one of the lowest per capita COVID incidence and mortality rates in the world. They have not had to close schools or use strict lockdowns.
An estimated 55 per cent of their infections occurred during the presymptomatic stage. A combination of early diagnosis of cases, plus contact tracing, plus 14-day quarantine of close contacts (regardless of symptoms) was estimated to decrease the reproduction number from 2.5 (each infected person infects 2.5 other people) to 1.5 people. (Remember, to stop spread, it is necessary to have the infection rate less than one.)
The effect of social distance and face masks reduced the reproduction number to 1.3, meaning that voluntary populationbased interventions, if used alone, were not enough to stop spread. Combining quarantining and contact tracing plus social distance and masks reduced the reproduction number to 0.85, successfully stopping spread.
Taiwan demonstrates that stopping the COVID-19 pandemic requires the collaboration of public health professionals and the general public. Either strategy alone would be insufficient.
The behaviours that are most effective at reducing spread in Taiwan are also effective in Canada. We are just not applying them strictly. But if we did, we would see the benefit. A study that tracked peoples’ movements using smartphone data from March 15, 2020 until March 6, 2021 showed that average time spent outside the home in a three-week period predicted the increased spread of COVID-19. It showed that low levels of mobility will control disease spread. (I doubt any of us is surprised at this, as we have witnessed the numbers go up when our activity is less restricted and fall again after lockdowns curb movement in our community.)
This study measured weekly growth rate – the ratio of cases in a given week compared to the previous week – and evaluated the effects of average time spent outside the home in the previous three weeks. The researchers tracked variation from week to week among regions and provinces.
Across the 51-week study period, 888,751 people were infected with SARS-CoV-2. Each 10 per cent increase in population mobility was associated with a 25 per cent increase in weekly case growth rate. Before the pandemic we had no restrictions on our movement, so mobility at pre-pandemic baseline was 100 per cent. Mobility measured during the study was highest in the summer (69 per cent) and dropped to 54 per cent in winter 2021.
The study concluded that use of smartphone data can be used to guide provincial and regional loosening and tightening of physical distancing measures. Mobility strongly and consistently predicts weekly case growth, and low levels of mobility are needed to control COVID-19.
