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We Swedes have been involved in this debate before. This spring, it was rumored that the Swedish crown’s strategy was to achieve herd immunity. The Swedish Public Health Agency and the government have repeatedly denied that the strategy is herd immunity. But the perception has survived. At the time, herd immunity was an insult.
After the summer, attention turned again to Sweden. With a low spread of the infection despite record testing, few treated with IVA, and few deaths compared to spring, other countries began to speculate whether Sweden might have done the right thing after all, perhaps we were protected by increased immunity in the population. But cases are increasing here too.
The spread of the infection is intense in many parts of Europe and the United States at this time. Many countries are tightening restrictions and planning new closures.
Three teachers believe that these closures and restrictions do more harm than good and wrote the Great Barrington Declaration. There, they suggest that life should return to normal for those who are not at such high risk of becoming seriously ill from COVID-19 with the goal of building herd immunity until there is an effective vaccine. Meanwhile, vulnerable groups must be protected.
It wasn’t long before other well-known scientists created the appeal of the John Snow memo (not from the TV series Game of Thrones, but from the father of modern epidemiology). Allowing the virus to spread in lower-risk groups will ultimately lead to increased morbidity and mortality throughout the population, they say. Measures to reduce the spread of infection must be introduced on a broad front and the ill effects must be managed with different types of support.
Both appeals have received thousands of signatures.
Flock immunity is an old concept in epidemiology, which means that a significant part of the population is immune to infection, either from a history of disease or from vaccination, or a combination of both. If the group is immune large enough, the virus has a hard time spreading. In this way, those who are not yet immune are protected. The more contagious a disease is, the more people must be immune before the flock’s limit of immunity is reached. Measles, which is extremely contagious, requires about 95 percent immunity. We don’t know exactly where the cutoff goes for covid-19, different analyzes come to different conclusions. But the level is between 40 and 70 percent.
Today we mainly arrive the limit of herd immunity with the help of vaccines, but for example, the Zika outbreak in South America ended without a vaccine. Even for the new coronavirus, we will achieve herd immunity over time, it is inevitable. The question is whether it is through an infection, a vaccine, or a combination of both.
Anyone who wants to quickly achieve herd immunity can remove all restrictions. The elderly and those with underlying diseases will be severely affected and many will die. Medical care can also be burdened with even more deaths as a result. Allowing groups at low risk of serious diseases to develop immunity can also lead to many people sick and dead, as spring has shown us that it is difficult to protect groups at risk when the expansion of society is great. Even young people without underlying illnesses can become seriously ill and die from COVID-19, but the risk is low.
Therefore, the path to herd immunity can be expensive without a vaccine. Also, immunity in flocks does not mean that the virus disappears automatically, but it becomes more difficult for it to spread. The spread of infection is not as rapid until the flock’s limit of immunity is reached; the more people who are immune, the slower the spread.
But herd immunity isn’t something that lasts forever, either. It depends on how long the immunity lasts and how much the virus mutates, but also on the fact that children are born and people move or travel. Before the measles vaccine existed, we had recurring outbreaks every few years when enough children were born.
The closure of communities has also important consequences for public health. It can result in unemployment, mental illness, hunger, increased abuse in the home, and more deaths from other illnesses. Additionally, there is no evidence that full closures are more effective in reducing the spread of infection than targeted measures, according to the European Agency for Disease Control (ECDC).
But the options are not simply to let the virus spread unhindered or to turn everything off. It is important to do as much harm to the virus as possible with measures that involve as little harm as possible to people and society until an effective vaccine is available. The way to do it may vary between countries and is more complex than that contained in the research calls.
