A Simple Mathematical Tool to Help Distribute Doses of ‘Two-Dose’ Covid-19 Vaccines among Non-Immunized and Partly-Immunized Population
Authors: Kapoor Aanandita , Kapoor Krishan Mohan 
Published: May 2021

Background

Full immunization with two doses of Covid vaccine has been found to be a critical factor in preventing morbidity and mortality from the Covid-19 infection. However, due to the shortage of vaccines, a significant portion of the population is not getting vaccination in many countries. Also, the distribution of vaccine doses between prospective first dose recipient and second dose recipient is not uniformly planned, as seen in India’s various states and union territories. It is recommended to give second vaccine doses within 4-8 weeks to first dose recipients for both the approved vaccines in India; hence the judicious distribution between non-immunized and partly immunized populations is essential. Managing the Covid-19 vaccination drive in an area with a large number of single-dose recipients compared to a smaller number of fully immunized people can become a huge administrative challenge. Therefore, this study was conducted to assess the number of people covered under the Covid vaccination drive in India and analyze the state-wise distribution of vaccines among the non-immunized and partly immunized population.

Methods

The Covid 19 vaccination data till 7th may, 2021 was taken from the website of the Ministry of Health and Family Welfare, Govt of India. From the data available of the number of doses injected, other figures like the total number of people vaccinated, people with two doses of vaccine or full immunization (FI), and those with a single dose of vaccine or partial immunization (PI) were found. The percentage of the fully immunized and partly immunized population was also found. A ratio between fully immunized and partly immunized individuals (FI: PI) was proposed as a guide to monitor the progress of the vaccination and future dose distribution of ‘two-dose’ Covid-19 vaccines among partly immunized (PI) and non-immunized (NI) population.

Results

In India, till 7 May 2021, 16,49,73,058 doses of Covid-19 vaccines have been injected. A total of 13,20,87,824 people received these vaccine doses, with 9,92,02,590 people getting a single dose or were partly immunized (PI), and 3,28,85,234 got two doses each or were fully immunized (FI). Among the states, Tripura and Andhra Pradesh had the highest FI: PI (Fully Immunized: Partly Immunized) ratio of 0.86 and 0.52, followed by Tamil Nadu, Arunachal Pradesh, and West Bengal with figures of 0.48. 0.47 and 0.47, respectively. Telangana and Punjab had the lowest FI: PI ratio among the states at 0.2 each, with Chhattisgarh, Madhya Pradesh, and Haryana following at 0.21. 0.23 and 0.23, respectively. These values are much lower than the national average of 0.33 in India.

Conclusion

The FI: PI ratio could help governments decide how to use scarce vaccine resources among first-time and second-time recipients. This simple mathematical tool could ensure full immunization status to maximum people within the recommended 4-8 week time window after the first dose to avoid a large population group with partly immunized status.