While population immunity is still below the classic 60 percent level, it may be enough to effectively stop the Covid-19 epidemic in Sweden, one of Denmark's most prominent epidemiologists has suggested.
“There are indications that the Swedes have gained an level of immunity to the disease, which, together with other measures in place, is enough to keep the disease down”, Kim Sneppen, a professor of biocomplexity at the Niels Bohr Institute in Copenhagen, told the newspaper Politiken.
Sweden registered a daily average of 23 cases per million people over the past week, compared to 61 cases in Denmark, whose infection rate now has surpassed peak figures from April.
At the same time, Sneppen acknowledged that Sweden had suffered a much higher death rate than that seen in Denmark (with nearly 5,900 deaths compared to 635).
“This is the price they have paid. On the positive side, they may now be finished with the epidemic,” Sneppen said.
An earlier study by professor Tom Britton at Stockholm University estimated that the threshold for full herd immunity might be as low as 43 percent of the population, which is far below the classic figures of 60-70 percent accepted in epidemiology. The basis for this is the assumption that the most sociable and active members of society are the first to get infected.
“Just 20 percent immunity makes a pretty big difference, because those who were infected at the start of the epidemic were the most susceptible to the coronavirus and the most socially active,” Britton said.
Søren Riis Paludan, a professor of biomedicine at Aarhus University, said that more and more evidence suggested that the Public Health Agency of Sweden may have been right in choosing to pursue a strategy that allowed for a controlled development of immunity.
“It can be argued that they chose the right solution, but they were poorly prepared for the strategy at the beginning and could not protect their vulnerable”, Riis Paludan said.
Sweden, whose no-lockdown approach in a bid to attain herd immunity has been criticised by medical professionals, politicians and activists alike, has seen slightly over 88,000 coronavirus cases, with its trajectory slowly receding from the peak figures registered in June. Denmark, by contrast, has seen nearly 29,000 cases, nearly three times fewer, but is in the midst of a fresh spike. Danish state epidemiologist Kåre Mølbak warned that Denmark was still in the “first wave of infection” because the wave in the spring did not have time to “fully develop” because the country “went into hibernation”.
However, the risk of further outbreaks in Sweden cannot be ruled out, other epidemiologists warned.
“I do not think that it can already be ruled out that Sweden will also have a flare-up like the one in Denmark”, Allan Randrup Thomsen, a professor of virology at Aarhus University, said.
Sweden's death rate is the fifth-highest per capita rate in Europe, but the number of new infections has been declining steadily since the peak in late June. As of today, it has merely a dozen patients in intensive care. This is a stark contrast to other countries in Europe that went into full lockdowns, such as Britain, France and Spain, where new cases are soaring, putting a damper on economic development.