The figure dropped slightly to 21% when vaccinated population were excluded
The novel coronavirus disease (COVID-19) is entering its third year. How many have been infected so far?
We only know of those who have tested positive following an RT-PCR (reverse transcription–polymerase chain reaction) or a rapid antigen test, but the disease manifests itself in other ways as well. Several people remain asymptomatic, making it difficult to truly gauge the spread of the virus.
A preprint published in medRxiv by the World Health Organization’s United Study Collaborator Group analysed over 700 standardised population-based sero-prevalence studies between January 2020 and April 2021.
It estimated that 26.1 per cent of the global population had antibodies against SARS-CoV-2 in April 2021, the figure dropped slightly to 21 per cent when those who were vaccinated were excluded. It was 8.3 per cent in October 2020.
A region-wise breakup revealed a stark variation. In December-April 2021, only 1.6 per cent of the population in the Western Pacific region had antibodies against SARS-CoV-2; it was 43-46 per cent in southeast Asian region, the Eastern Mediterranean region and the African region; 33 per cent in high-income countries in the European region.
The figure for high-income countries in the Americas was the highest, at 57 per cent.
The figure was 51 per cent in December 2020 for low-middle income countries in Europe. For the same income group of countries in the Americas, the figure was 21 per cent.
While every region has reported a rise in the percentage of the population that has antibodies against COVID-19, the reason varies from one place to another.
The study said:
This timeline shows rapid increases in sero-prevalence since December 2020 due to infection in some regions — up from 18 per cent to 46 per cent in Africa — and vaccination and infection in others — from 11 per cent to 57 per cent in high-income countries in the Americas — while seroprevalence in other regions remains low — 0.3 per cent to 1.6 per cent in the Western Pacific Region.
Of the 194 WHO member states, 88 were represented in these studies. In Africa, 16 of 47 members were represented; 11 of 21 members and one territory in Eastern Mediterranean; 12 of 35 members and one territory in the Americas; 36 of 53 members and two territories in Europe; five of 11 members in South-East Asia; and eight of 27 members in the Western Pacific were included in the studies.
The results arrived upon by the study revealed a severe under-ascertainment of cases, “indicating that many cases of SARS-CoV-2, including subclinical cases, are not captured by surveillance systems which in many countries are based on testing of symptomatic patients.”
The missed detection was calculated seroprevalence-case ratios, which remained wide across all regions, countries of varying incomes and time.
These estimates were in resonance with the findings from several studies in the Americas, Europe and southeast Asia. There were no such analyses from the Eastern Mediterranean region, Africa and the Western Pacific regions of the WHO.
The study also found an age-wise breakup of antibody presence, with “children aged less than 10 years, but not children aged 10-19, were less likely to be seropositive compared to adults aged 20-29 years; similarly, adults aged above 60 years, but not those aged 30-39, 40-49, or 50-59, were less likely to be seropositive than adults 20-29.”
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