TOKYO -- The global population may be closer than expected to the critical level of herd immunity needed to reopen business and public activities safely, a recent coronavirus study suggests, but problems with testing make this hard to determine.
A survey in New York indicates that the number of people who have been infected by the virus could be 10 times higher than the official case count, the state said Thursday.
Tests conducted on 3,000 randomly selected individuals show the presence of coronavirus antibodies in 13.9% of the group. This rate would extrapolate to 2.7 million residents statewide having contracted the virus, far more than New York's 270,000-plus confirmed cases.
Wuhan, the Chinese city where the pandemic originated, began testing roughly 11,000 people for antibodies on April 14. The results will be released shortly. Similar testing will occur in nine other Chinese cities, including Beijing.
Antibodies in a person's blood indicate an immune response to infection. Their presence might mean the individual has built up immunity to reinfection, which could make it safe to reopen a community once enough people are immune.
So-called herd immunity can arise in a population if at least 60% possess resistance to a disease.
Because many coronavirus cases are either asymptomatic or mild, it has been suspected that the number of infections far exceeds the confirmed counts. But estimates from the World Health Organization suggest that the world has ways to go before it reaches the 60% mark.
"Early data from some ... studies suggest that a relatively small percentage of the population may have been infected, even in heavily affected areas, not more than 2% to 3%," WHO Director-General Tedros Adhanom Ghebreyesus said Monday.
Efforts to expand antibody testing are gaining steam amid the long-term fight against COVID-19. The U.S. Centers for Disease Control and Prevention will collect and test 50,000 samples in September and December of this year, and in November 2021. The nationwide survey will determine the extent of the epidemic and assist in the development of vaccines.
Some anticipate partial reopening of economies if antibody carriers are identified. Britain recently floated the idea of issuing "immunity passports" allowing holders to travel freely outdoors.
However, efforts to expand antibody testing have run into problems.
India placed high hopes on antibody testing, recently importing about 700,000 kits from China and distributing them to various parts of the country with the aim of speeding up detection of coronavirus cases. But this week, the country's top medical research body asked states to stop using the Chinese-made tests for two days following reports of doubtful reliability.
Antibody tests also are less accurate in determining infections than conventional polymerase chain reaction tests, which screen for genetic material.
And it is unknown whether the presence of antibodies actually affords immunity against reinfection. South Korea has reported some recovered COVID-19 patients who later tested positive for the virus.
Reports in China indicate that roughly 30% of patients who recover do not develop a sufficient level of antibodies immediately afterward. The risk of a resurgent epidemic cannot be ruled out.
Another hurdle is the supply of antibody test kits. In Japan, Kurabo Industries is importing kits made by a partner manufacturer in China, but the kits will be sold only to research labs.
Drugmaker Shionogi & Co. is partnering with a biostartup to sell test kits made in China. But approval for sales of such new tests takes nearly a year under normal circumstances.
Japan's health ministry has asked the Japanese Red Cross Society to test the efficacy of multiple antibody test kits on donated blood. The results from 1,000 samples will be released around May 1.
Meanwhile, as the race to develop tests proceeds, COVID-19 continues to rage in Asia. Indonesia reported 436 new cases for the past 24 hours Friday, a new daily high, bringing the total to 8,211, with 689 deaths.
India also saw its biggest spike in a 24-hour time frame Friday as it confirmed 1,684 new coronavirus cases. The nationwide total has reached 23,077, with 718 deaths, according to the Ministry of Health and Family Welfare.