in his new location risk assessment The National Institute of Public Health settles on the concept of herd immunity in relation to the Corona epidemic, which they also did in press release in July. Instead, the WHO will emphasize that all vaccines help keep the COVID-19 epidemic under control in Norway.
The FHI wrote in the risk assessment that it is impossible to calculate a threshold value for herd immunity and that “it is not very feasible to speak of herd immunity as a dictatorial phenomenon where an individual has or does not have herd immunity”.
The term was mentioned frequently initially in the epidemic, particularly by Swedish health authorities. At one point, state epidemiologist Anders Tegnell estimated that one could achieve Herd immunity in Stockholm during May 2020.
Assistant Director of Health Espen Rostrop told Nacstad Dagbladet that he agreed with the FHI.
I agree with that, and I only used the term population immunity on purpose because it says something about the degree of protection in a society where immunity is not great enough to protect the whole herd, but it still has great significance. Nakstad told Dagbladet that it is not certain that any country will achieve true herd immunity to this pandemic, at least not for the foreseeable future.
It is likely that greater global immunity and a lower frequency of mutations in the coronavirus will be required before the virus disappears in the entire population during the summer. But in the end, the Corona virus may be absent in the summer, but it is present in the winter in Norway, although of course it is not certain.
The Norwegian Institute of Public Health explains that herd immunity means that the entire population is protected as a result because this large proportion is immune to becoming sources of infection, so that the virus cannot spread between the population.
“Theoretically, one should be able to calculate a threshold value for the proportion of immunity in the population needed to stop the epidemic.”
“If the epidemic spreads unimpeded in the population, this threshold is reached when the epidemic wave is at its peak. Then the effective reproduction number R is exactly 1, then R is less than 1, and the epidemic decreases. The spread of infection does not stop immediately. It takes some time before the epidemic ends, during which time many people become infected. This cut-off value is given by f = (R0 – 1) / R0 = 1 – 1 / R0″.
It is impossible to calculate
But the FHI believes that several factors make it impossible to calculate such a threshold value for the Corona epidemic in Norway, and lists the following four reasons:
- “The calculation assumes that the immune system is randomly distributed among the population and has a random contact pattern, and that infections between people are randomly distributed. It is unrealistic, and we don’t know its effect. For example, there may be pockets of unvaccinated people who may have an outbreak.”
- “Immunity in a population changes all the time: it can weaken over time, the virus can mutate and escape immunity to a large extent, children are born without immunity, more are immunized or infected, and people who are immune or not immune are transmitted to the country. “
- “We don’t know what the R number of the delta variant is in Norway right now.”
- We do not know for sure how vaccination protects against infection and transmission.
All vaccinations contribute
The main message of the FHI is that all vaccines help keep the COVID-19 epidemic under control in Norway: directly by reducing disease risk and indirectly by reducing the spread of infection.
They also write that indirect protection always helps to limit the spread of infection to a greater or lesser degree. In addition, they demonstrate how important protection is as the delta variant dominates the spread of infection:
- About 60-80 percent against infection.
- About 95 percent are against getting seriously ill.
- About 20-50 percent against transmission if you become infected for the first time.
FHI adds that several studies indicate that protection against infection decreases over time after infection or vaccination, while maintaining protection against serious disease.
We’ve seen that vaccine coverage has a lot to say about the evolution of the epidemic, and we may be in a position in Norway where the vaccine reduces the R number from somewhere between 5 to 10 in a non-immunized group to about 1. But unfortunately, the effect of the vaccine alone isn’t big enough to get an R-number below 1. It seems we’ll have to help a bit with infection control measures to deal with it — at least this winter, Naxtad’s assistant health director tells Dagbladet.
The Norwegian Institute of Public Health also wrote in the risk assessment that the seasonal effect may have contributed to the increase in hospitalizations in November of last year, and that this effect specifically may lead to an increased risk of contagion in the coming months.
This is due to the biological conditions in the interaction between the virus, man and the environment, and as a result of behavioral changes in winter.
The seasonal effect just means that we live more indoors during work and leisure hours than in hot weather. Therefore, the prevalence of infection usually increases in the winter, which is why influenza is more common in the winter rather than in the summer in Norway, says Nakstad of the seasonal effect on Dagbladet.
In 2020 and 2021, the peak admissions in Norway occurred in March and April.
– A year ago we saw that we reached the highest rate of epidemic and hospitalization in the middle of winter in eastern Norway, and there is a risk that the R number will go up due to a lot of indoor activities when the weather gets colder.
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