In this study, three infection disease models were constructed using the actual number of infections of COVID-19 from March 5 to April 15 in India. The results showed that when effective isolation and vaccination measures were taken, the number of infections will be greatly reduced by 99%.
During the second wave of epidemic in India, the number of newly confirmed cases rose rapidly every day. As of May 7, there were 401,326 newly confirmed cases per day, and 3,931,673 existing cases. Due to the sharp increase in cases and the shortage of medical supplies in the India federation, the medical and health system is on the verge of collapse, and the society is facing huge panic [5].
During the epidemic, in the absence of effective vaccine, isolation is an effective measure to control the spread of infectious diseases. Therefore, we incorporated isolation measures into the model, and simulated the impact of the measures of different intensities on the number of existing cases. The results showed that when the effective isolation rate of the infected population reaches 0.5, the current infections will continue to decline, and as the effective isolation rate increases, the decline will be further increased. The prediction results of the model suggested that isolation measure can effectively control the epidemic. In addition, even if the isolation rate is low and the epidemic rebounds again, the current number of infections as of April 15 is far smaller than the actual number of cases. During the second wave of the epidemic, the India government claimed to have implemented isolation measure to control the epidemic [10], however based on the model fitting results, the measures had little effect. According to reports, the Indian government was unable to guarantee the normal supply for residents during the implementation of isolation measures, as a result that residents sneaked out of their homes at the risk of being infected [11], which has led to the ineffectiveness of the isolation measures. On April 14, millions of Indians poured into the Ganges to celebrate the festival, providing a breeding ground for the spread of disease. Formulating of measures does not mean achieving the ultimate goal. After the measures were formulated, how to implement them smoothly and how to achieve the expected results are the issues that those in power should consider.
Vaccination is the most effective prevention method to control COVID-19 epidemic. In the current study, we assumed that all patients will be vaccinated within 70 days, then we incorporated the vaccination into the extended SEIR model and simulated the future epidemic trend within 100 days from the start of vaccination on March 5 to one month after vaccination. Currently, India has approved three vaccines-Covishield, Covaxin and Russia's Sputnik V, and their effective rates are 70.42%, 60% and 95%, respectively [12]. Therefore, we simulated the development of the epidemic of COVID-19 with vaccine effective rate of 50%, 70%, and 90%, under different coverage rates. The results demonstrated that with the increases of effectiveness of the vaccine and the number of people vaccinated, the India epidemic will hit an early inflection point.
The impact of vaccines on the trend of the epidemic has played an important role in guiding the prevention and control of the epidemic. The Indian government is currently expanding vaccine-manufacturing capacity and encouraging more individuals to be vaccinated. As of April 15th, more than 110 million people in India had been vaccinated, but judging from the actual number of infections, the current vaccination has not had a positive impact on the prevention and control of the epidemic. The possible reasons are as follows. First, In India, the priority population for vaccination is the upper class with relatively lower infection rate, however, people living in slums with high infection rate have a lower vaccination rate, which leads to most of the vulnerable population not being effectively protected [13]. Furthermore, the second wave of the epidemic in India was caused by a mutated virus strain, and the current vaccine maynot be effective as expected. Therefore, to better control the epidemic, the Indian government still needs to continue to expand the vaccination population and try to vaccinate more efficient vaccines.
There are several strengths of this study. First, additional factors were incorporated in the extended SEIR models, which makes the fitting effect of the model closer to the real situation. Second, this study provides guidance for early prevention and control of the epidemic under the circumstances that the underlying mechanisms of the delta coronavirus mutation remained unclear.
There are some limitations of this study. First, to better analyze the impact of isolation and vaccine factors on the epidemic, other parameters were combined and simplified as much as possible, which might lead to overfitting of the model. Second, the data used in this study was obtained from the WHO, and the authenticity of the data is subject to the official announcement. However, during the second wave of epidemic in India, the upper limit of single-day testing of medical institutions might affect the authenticity of the data. Finally, the model tends to predict more optimistic result than the actual situation. The current study predicted the vaccination situation in India based on the highest single-day vaccination in China, however, the current single-day vaccination in India was less than 3 million [14].