We quantified the size of the target population groups of COVID-19 vaccination stratified by province in China. The size of the target population shows large differences among provinces, ranging from 3.5 million to 115.2 million. To achieve the goal of vaccinating 40% of the target population by June 2021, the COVID-19 vaccination capacity (daily doses administered) has been highly improved compared to the routine vaccination capacity before the COVID-19 pandemic. Nevertheless, the speed of vaccine roll-out differs remarkably at the provincial level. The highest coverage occurs in Beijing and Shanghai (over 80% of the population was administered at least one dose, equivalent to 69.8% and 62.3% of the fully vaccinated population, respectively). However, in 9 of 31 provinces, less than 30% of the population was administered at least one dose by early June. The current vaccination capacity (even in terms of maximum daily doses administered) is far less than enough to achieve the target of 40% coverage by June in three provinces. Even on the basis of the maximum daily vaccination doses from December 2020 to May 2021, approximately 5 and 2 provinces will be unable to reach the vaccine target of 70% by the end of 2021 and the middle of 2022, respectively.
The Joint Prevention and Control Mechanism of the State Council in China released a three-step strategy for the COVID-19 vaccine rollout [13] on December 15, 2020. In the first step, nine groups of essential workers, aged 18 to 59, were prioritized because of their high risk of occupational exposure. In the second step, vaccination programs would focus on key populations that are vulnerable to severe outcomes once infected, including older adults aged ≥ 60 and people with underlying conditions. In the final step, vaccines are available to other general populations. The vaccination program has been gradually extended to residents aged 18–59 since approximately March 2021 and further extended to people over 60 since March 29, 2021 [32]. To vaccinate 40% of the population by June 2021 and 70% of the population by the end of 2021 or mid-2022, China invested significant efforts into promoting coverage. Estimating the size of target priority groups at the provincial level could support local governments to determine the coverage rate stratified by target groups, and thus to timely determine and adjust vaccination policies and promotional measures.
Currently, COVID-19 vaccines are ineligible for pregnant women. In developed countries, such as the United States, pregnant women have been recommended to receive the vaccine, even with limited data on safety and efficacy [36, 37]. Clinical trials in pregnant women have been launched for several vaccines abroad [38]. In our analysis, we considered pregnant women as a target population group, accounting for the increased risk of severe illness among pregnant women, such as preterm delivery [39]. However, high vaccine hesitancy among pregnant women, which occurs in influenza vaccination in China [40, 41], will most likely be a major challenge for the implementation of COVID-19 vaccination in this group, even though the vaccine has been proven to be safe and effective in the future. If we exclude pregnant women from vaccination, the target population size in each province would decrease by approximately 1.8%.
To accelerate the COVID-19 vaccination and achieve herd immunity as early as possible, a series of measures have been implemented across China, including setting up temporary inoculation points, extending the service hours of inoculation points and even opening night vaccination sites, and rolling out mobile vehicles and even offering vaccines door-to-door for those with poor geographical access. [42] Under the joint efforts of central and local governments, the daily vaccination doses have exceeded 15 times the routine capacity (22.9 million vs. 1.4 million). Nonetheless, great disparities exist in vaccination progress across provinces. For example, more than half of the residents in Beijing and Shanghai have been fully vaccinated, whereas the one-shot vaccination proportion is so far around 30% in most provinces. The disparities could be largely determined by the national vaccination strategy at the previous stage. Priority is given to areas with higher risks of COVID-19 outbreaks [43], such as Beijing and Shanghai, which are characterized as the largest port cities and the most populous and largest megacities.
Our findings show that COVID-19 coverage until now has been very low in some provinces. It is a major challenge to achieve the coverage targets of 40% and 70% within the specified timeframe, particularly for provinces with large populations (e.g., Henan and Hebei provinces). When and to what extent we could remove NPIs does not depend on the time when the provincial-level vaccine coverage first reaches the herd immunity threshold, but the time when the last province reaches the herd immunity threshold. The earlier removal of NPIs in provinces with high vaccine coverage (always developed regions with better healthcare services) definitely increases the risk of the transmission of SARS-CoV-2 in other provinces with low vaccine coverage, which have limited healthcare resources and poor healthcare accessibility.
In addition to the aforementioned national vaccination strategy, other factors, such as the vaccine supply, varying strengths of local implementation measures and the willingness to receive the COVID-19 vaccination, could also influence vaccination progress. The domestic production capacity is expected to reach 5 billion doses this year [44], thus vaccine supplies would be adequate. The vaccine hesitancy rates varied among provinces and were above 30% in 20 provinces [45]. The skyrocketed increase in the number of local populations that received the vaccination after COVID-19 outbreaks occurred in Anhui and Guangdong provinces [46], indicating that stimulating people to receive the vaccination would be crucial to achieving herd immunity as soon as possible.
In this study, we estimate the vaccination capacity needed to reach a coverage target of 70%. Note that it is not a precise estimate of the herd immunity threshold. Instead, it is estimated on the basis of the well-known Eq. (1 − 1/R0)/VE[47], where R0 is the basic reproduction number and VE denotes vaccine efficacy. It ignores heterogeneities that can make these figures biased in specific locations, including social mixing patterns and age-specific susceptibility. Accordingly, it has been highlighted that the provinces could not stop the vaccination when reaching the target coverage of 70%. Further modeling studies are needed to determine the exact herd immunity threshold and when and to what extent we could remove NPIs for specific regions.
Several limitations of our study should be mentioned. First, some provinces only announced their cumulative administered doses. To estimate the number of people who are fully vaccinated, we assume a uniform two-dose schedule and simplistically divide the overall doses by two. However, the available data in some provinces indicate that the proportion of individuals receiving the first dose is much higher than the proportion receiving the second dose. Accordingly, we might overestimate the proportion of people who are fully vaccinated. Second, only Beijing and Shanxi established a system to report daily vaccination status [48, 49]. For other provinces, we manually collected information through several search engines, which may affect our data integrity. Accordingly, the maximum service capacity is probably a conservative estimate, due to scarce data points for provinces, such as Heilongjiang, Jiangsu, Fujian, Yunnan, Tibet and Xinjiang.