IUSSP International Population Conference 2021
The 29th International Population Conference brought the global demography community together in a fully virtual format — the first IPC in its nearly 100-year history held entirely online. Despite being shaped by COVID-19, the conference attracted its broadest-ever international participation and produced a body of research that is still widely cited for its documentation of the pandemic's demographic consequences.
About IUSSP and the International Population Conference
The International Union for the Scientific Study of Population was founded in 1928 and is the oldest and most internationally representative organisation in demography. It currently counts over 3,000 individual members and 70+ national associations across every world region. Unlike the PAA, which is primarily North American in membership, the IUSSP draws heavily from researchers in Asia, Africa, Latin America, and Europe, giving its conferences a genuinely global character.
The International Population Conference is held every four years — comparable in prestige and scale to the Olympic cycle in its field. Past conferences were held in Salvador (2001), Tours (2005), Marrakech (2009), Busan (2013), and Cape Town (2017). The 2021 edition was the 29th, originally planned for Hyderabad's HICC convention centre before moving online. The IUSSP also publishes the International Studies in Population book series, which frequently incorporates IPC research.
The COVID-19 shadow over demographic data
No theme dominated IPC 2021 more than the demographic consequences of COVID-19. The pandemic had disrupted data collection — censuses were postponed in dozens of countries, civil registration systems were overwhelmed, and household surveys were suspended — creating gaps in the very datasets demographers rely on. Sessions were devoted to methodological responses: how to adjust mortality estimates when death registration was incomplete, how to model excess mortality when official COVID counts were known to be undercounts.
Excess mortality analysis emerged as the most debated topic. Researchers from the WHO and the Economist Intelligence Unit's excess death tracker both presented early estimates suggesting true COVID deaths were two to five times the officially reported figures in many low- and middle-income countries. This had direct implications for life expectancy at birth estimates: the US saw a two-year drop between 2019 and 2021, the largest single decline since World War II. Russia, Peru, and several Eastern European countries showed even steeper declines in preliminary data reviewed at the conference.
Fertility in a pandemic year: baby bust, not baby boom
Early speculation that lockdowns might produce a "baby boom" was definitively refuted by IPC 2021 research. Preliminary birth data from Europe, North America, and parts of Asia presented at the conference showed a consistent pattern: births fell sharply nine months after lockdowns began — a "COVID baby bust" concentrated in already below-replacement countries. Italy, Spain, and Japan saw birth declines of 8–12% in late 2020 and early 2021.
Researchers debated whether this was a genuine decline in fertility intentions or a postponement that would reverse in subsequent years. The Demographic Research special collection on COVID and fertility (open access) compiled much of the initial evidence. By 2022 some recovery was visible in several countries, but it was partial — not a full reversal — suggesting a portion of the "missing births" reflected permanent foregone fertility rather than delay.
In high-fertility countries the pattern was more complex. In parts of sub-Saharan Africa, sessions noted that disrupted contraceptive supply chains and interrupted family planning services during lockdowns had in some areas temporarily increased birth rates — a reminder that the demographic transition is not a one-directional ratchet. Detailed country-level TFR data from this period is now incorporated into the UN WPP 2024 estimates.
The sub-Saharan Africa data challenge
A recurring concern across IPC 2021 sessions was the persistent weakness of demographic data infrastructure in sub-Saharan Africa — the region that will account for the majority of global population growth through 2100 and is therefore the most consequential uncertainty in any long-run projection. Three interlocking problems were identified:
Census gaps. Several major countries — including Nigeria, the continent's most populous — had not conducted a census for over a decade before the conference. COVID caused further postponements. Without reliable census baselines, estimates of current population size carry wide uncertainty. The UNFPA's census programme was highlighted as underfunded relative to need.
Civil registration gaps. Fewer than 50% of births and deaths are registered in many sub-Saharan African countries, according to data from the WHO civil registration programme. This makes it impossible to compute reliable life tables or natural increase rates from administrative data alone, forcing reliance on survey-based estimates with their own limitations.
Innovative data alternatives. Sessions on data innovation attracted significant attention — researchers from the WorldPop project at the University of Southampton and the Meta Data for Good initiative presented high-resolution population density maps derived from satellite imagery and mobile data. These approaches can produce population estimates at 100-metre grid resolution even without a census, and are increasingly being used by humanitarian organisations for planning. Their integration with official statistics remains a methodological frontier.
Migration, displacement, and the pandemic border
International border closures in 2020–21 created a natural experiment in what happens when migration flows are suddenly interrupted. Sessions analysed the demographic consequences: labour-sending countries like the Philippines and Bangladesh saw sharp declines in remittance-supported household income, while receiving countries faced acute shortages in sectors heavily dependent on migrant workers — aged care, agriculture, construction, and healthcare. The IOM World Migration Report 2022, previewed at IPC, documented these disruptions systematically.
Internal displacement received extended attention, with sessions drawing on UNHCR Global Trends data showing a record 82 million forcibly displaced people globally by mid-2021. Researchers examined both conflict-driven displacement (Syria, Yemen, South Sudan) and climate-related internal migration — a topic gaining urgency as the evidence base for future climate displacement grows. The implications for standard net migration accounting, which treats internal and international flows separately, were discussed in methodology sessions.
Selected notable sessions
Estimating excess mortality from COVID-19 in data-sparse settings
Cross-national comparison of excess death estimation methodologies, reconciling official COVID counts with civil registration data and modelled baselines. WHO and The Economist excess mortality datasets were central references; full WHO estimates are now available at the WHO global excess deaths page.
COVID baby bust: evidence from high-income and middle-income countries
Comparative analysis of birth rate changes nine months post-lockdown across 30 countries. Researchers debated postponement vs permanent foregone fertility, with analysis published in the Demographic Research COVID fertility special issue.
High-resolution population mapping without census data: satellite and mobile data approaches
WorldPop and Meta Data for Good researchers presented gridded population estimates at 100-metre resolution for sub-Saharan Africa. Methods documentation available at the WorldPop methods page.
Climate displacement: from theoretical models to observed internal migration
Drawing on World Bank Groundswell projections and UNHCR displacement tracking, sessions examined how climate-related shocks are already producing measurable population movements in Bangladesh, the Sahel, and the Pacific. UNHCR Global Trends data was used extensively.
COVID-19 and older populations: excess mortality, care systems, and long-term demographic impact
Analysis of COVID's concentration in older age groups and what it implies for life expectancy trajectories, dependency ratios, and the sustainability of long-term care systems already under pressure from ageing. OECD long-term care data provided the comparative framework.
Legacy and the road to IPC 2025
IPC 2021's virtual format, while forced by circumstance, demonstrated that global participation barriers can be substantially reduced when travel is not required. Researchers from Nigeria, Bangladesh, Ethiopia, and other lower-income countries attended and presented at rates well above their typical IPC representation. The IUSSP has since incorporated hybrid elements into its planning for future events.
The conference's research output fed directly into subsequent data products. The excess mortality analysis shaped WHO's official 2022 revision of COVID death estimates. The fertility postponement research informed the UN WPP 2024's revised near-term fertility schedules. The satellite mapping work has become standard in humanitarian operations contexts and is incorporated into population layers used by the UN Office for the Coordination of Humanitarian Affairs (OCHA).
The next International Population Conference — IPC 2025 — is scheduled to be held in Hamburg, Germany, returning the event to an in-person format for the first time since Cape Town 2017. Abstract submissions opened in 2024. Papers from IPC 2021 and prior conferences are searchable through the IUSSP paper search archive.
Frequently asked questions
What is the IUSSP International Population Conference?
The IPC is held every four years by the International Union for the Scientific Study of Population, founded in 1928. It is the largest global demography conference, drawing researchers from over 100 countries across demography, economics, epidemiology, and social science. Unlike regional meetings such as the PAA, the IPC is intentionally global in scope and participation.
Why was IPC 2021 held online?
The conference was originally planned for Hyderabad but shifted to a fully virtual format due to COVID-19 travel restrictions. The virtual format unexpectedly enabled the broadest-ever international participation in an IPC, with researchers from lower-income countries attending at higher rates than any previous in-person edition.
What were the central research findings?
Key findings included COVID-19's severe impact on life expectancy and mortality data quality, a global "COVID baby bust" rather than a baby boom in high-income countries, persistent data infrastructure gaps in sub-Saharan Africa, and methodological advances in satellite-based population mapping. Research from IPC 2021 directly informed the UN WPP 2024 revisions.
Where can I find IPC 2021 papers?
Presented papers are searchable through the IUSSP paper archive. Many are also published in open-access journals including Demographic Research and Population Studies.
When is the next International Population Conference?
IPC 2025 is scheduled for Hamburg, Germany — the first in-person IPC since Cape Town 2017. Details and the abstract submission portal are available at iussp.org.