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The word herd immunity has almost become a benchmark during this pandemic. For example, it has been used by Trump (he really just said “the herd”) to show that the Swedish strategy without hard closings is a failure and that one is sacrificing individuals to achieve herd immunity.
He is not the only one who has misunderstood this. The Public Health Authority and the government have repeatedly denied that herd immunity would be Sweden’s strategy. Instead, the Swedish krona’s strategy focuses on leveling the curve and reducing, but not completely stopping, the rate of spread of the infection, although not to the same extent as most other affected countries. A side effect of the strategy is that a large proportion of infected people in society can reach the limit of collective immunity. Government officials have repeatedly spoken positively about the herds’ immunity, which may have contributed to the confusion.
Flock immunity means that enough people in a population are immune to the spread of disease. It is achieved through vaccination or infection, where those who are immune form protection for those who are not.
The more contagious a disease is, the greater the proportion of the population that needs to be immune. Measles is one of the most contagious diseases in existence, and therefore it is estimated that at least 95 percent of a population must be immune to reach the herd’s immunity limit.
The proportion of the population that has had covid-19 in different countries varies greatly, but according to preliminary estimates, only a small proportion carry antibodies and, therefore, have had the disease.
We currently do not know what proportion of immunity is required to achieve collective immunity for covid-19. In the past, it was estimated that approximately 60 percent immunity was required. Two new but unpublished and unexamined models come in at a lower figure, around 40-45 percent.
What proportion of the population? Those who have had covid-19 in different countries vary widely, but according to preliminary estimates, only a small proportion carry antibodies, and therefore have had the disease. According to the WHO, these studies vary from 1 to 10 percent in US studies. USA, Europe and Asia. A new but preliminary study of the battered Spain suggests that only five percent of the population carries antibodies. In Madrid, the figure was eleven percent.
Read more: Spanish study on antibodies does not worry Tegnell
This indicates that the many sick people we have seen may not be just the tip of an iceberg, so there would actually be many people in society who became infected but never became sick. The public health authority does not see it in its investigations either. Symptoms may be mild, but those with no symptoms are probably only a small proportion. The WHO has repeatedly noted that many of those who are considered asymptomatic in studies are likely to have no symptoms at the time of the trial and will become ill later.
Mike Ryan, WHO chief In preparation for the crisis, he warned this week that countries seeking to obtain herd immunity as soon as possible can pay a heavy price for many deceased older people. Antibody study studies indicate that the herd’s immunity may be far away.
Mike Ryan.
Photo: Salvatore Di Nolfi / AP
However, there is great uncertainty about antibody testing. In part, it is not certain that they will catch everyone who has antibodies, and second, other parts of the immune system may be involved in immunity. We still don’t know whether even those who have had very mild or symptom-free symptoms also develop antibodies.
The Public Health Authority has in the past It is estimated that around 25 percent of Stockholmers must have or have had covid-19 in mid-May. Sounds loud when you look at survey results from other countries and also from other big cities. But it is too early to say whether the authority has been wrong. As so often during this outbreak, we have to hold on before we can get a clearer answer. Next week, the authority will provide an analysis of how many in Stockholm and the rest of the country have had covid-19.
But 25 percent in some countries is still a good piece of collective immunity. And even though the magic limit for herd immunity is reached, there is still a relatively large group that has no protection. The spread of infection may not stop completely, but it may be much slower. Therefore, everything cannot go back as before for a region of Sweden to obtain herd immunity, especially not for the elderly who are at the highest risk of becoming seriously ill and dying.
How I have written In the past, another problem with collective immunity is that we don’t know how long immunity lasts. Most researchers agree that anyone who has had covid-19 will receive protection, but it doesn’t matter how strong the protection is and how long it lasts. Most indicate that immunity may be a year, but that it declines over time. If the immunity is short, the immunity of the herd may soon decrease in society and the disease again begins to spread.
We may not achieve true herd immunity until there is a covid-19 vaccine.
