Islamabad, July 20 : Pakistan's total population is estimated at 220.9 million and it is growing rapidly with an annual fertility rate of 3.6 children per couple, according to a report. The 2020 World Population Data Sheet, released by the US Population Reference Bureau, also estimates that the world today has a total of 7.8 billion inhabitants, Dawn news reported on Monday. Referring to the COVID-19 crisis, the report warns that "population density in urban areas, household size, and population aging contribute to our vulnerability to pandemics". The report placed South Asia among the fastest growing regions in the world and within the region, it marks Afghanistan and Pakistan as the fastest growing populations. Afghanistan has a faster growth rate than Pakistan, 4.5 per couple. But because of high death rates and low life expectancy, the country's total population is still 38.9 million. At Pakistan's growth rate Â? 3.6 Â? a population doubles in 19.4 years. A country needs to bring its growth rate down to 2 per cent a year to reduce its population. The replacement fertility rate is 2.1, the average number of children a couple needs to have to replace themselves, according to the report. With a total of 1.424 billion people, China still has the largest population in the world but has been able to reduce its fertility rate to 1.5. The Asian giant's population is projected to decrease by 2050. With 1.4 billion people, India has the second largest population in the world but has reduced its fertility rate to 2.2, the report revealed. /IANS