[ad_1]
Coronavirus
The big question about herd immunity continues: how many should be immune now?
Until now, it was thought that between 60 and 70 percent of the population would have to be immune to stop Sars-CoV-2. But: the mutated virus also changes this.
In Manaus, Brazil, 66 percent of the population had antibodies to the virus in their blood after the first wave. A second wave did not follow, but cases still exist.
The coronavirus, that is clear, cannot be eradicated. This is impossible, especially with viruses that also circulate in animals. In the case of viruses, such as poliovirus, which only circulates in humans, the population can be vaccinated until a virus no longer finds individuals whose immune systems are not yet ready for it.
In the case of coronaviruses, there is also the fact that immunity does not last for life (unlike diseases such as measles or rubella). As a general rule, you are only protected for one to two years after a coronavirus infection. It remains to be seen whether this also applies to the new virus.
The virus has to become endemic
Still, the pandemic will come to an end when enough people are immune, through vaccination or infection. So the virus is “just” endemic, which means that the pathogen continues to circulate, but the disease only occurs sporadically and sometimes as a localized outbreak.
This is herd immunity: so many people are immune that many chains of infection are broken and the spread is greatly slowed down. Good protection of the dough can hardly be achieved by natural infection, precisely because the spread slows towards the end.
Without repeated vaccinations it won’t work
There are theories that suggest that for natural group immunity, less percent of the population must be immune. This is because an epidemic hits the most susceptible people and those with many contacts first.
If they are immune, the spread is slower than if an equally high percentage of the population were vaccinated, which also includes people who would hardly have spread the virus. However, if the immunity does not last a lifetime, it will not work without repeated vaccinations.
The World Health Organization (WHO) and many epidemiologists assume that Sars-Cov-2 is herd immunity in 60 to 70 percent of infected or vaccinated people in a population. This is because the infection rate (the famous R value) of the coronavirus is 2 to 3 without protective measures. This was the result of calculations since the beginning of the pandemic, when social distancing and other measures had not yet been introduced.
To contain an infectious disease, the R-value must be below 1. If two out of three newly infected people are already immune, the epidemic should decrease significantly. Two out of three percent are 66.7, hence the assumption for Sars-CoV-2 herd immunity of 60 to 70 percent.
If the virus is more contagious, more immune systems are needed
But the infection rate is not a fixed amount. Depending on the mobility and way of life of the population, it may be lower or higher. And it increases when the virus becomes more contagious, as is now the case with the England mutation. The more contagious a virus is, the more people need to become immune to stop an epidemic. For measles, one of the most contagious diseases of all, the R-value is between 12 and 18. 95 percent of the population must be vaccinated before herd protection takes effect.
Real world scenarios suggest that herd protection cannot be less than 60 percent. Meanwhile, antibody measurements have shown that there are already cities and regions in the world where 60 percent or more of residents have antibodies against the virus, such as in Bergamo (62%) or Manaus in Brazil (66%) a late first wave. In Manaus, for example, there are still infections and deaths, but there was no second wave after the summer and the rates remain low.
Other reports are less representative, such as those from ships or prisons, because the probability of infection, that is, the R-value, is higher in these small cell locations than in a population that lives less closely. On the French aircraft carrier Charles de Gaulle, 68 percent of all military personnel were infected in an outbreak in March before the crew went into quarantine on the ground. At San Quentin State Prison in California, more than 60 percent were infected until action was taken.
Tanner: “Switzerland must take care of the cities”
When vaccinating, the focus is not only on people at risk, but also specifically on densely populated areas: there immunity should be higher. “Switzerland has to take care of the metropolitan areas,” says task force member and epidemiologist Marcel Tanner.
And he also points out: “Time also plays an important role.” This is known from the half-carried out vaccination campaigns against childhood diseases in some countries, where disease outbreaks continue to reappear.
No one has yet comprehensively modeled how the most contagious virus changes the required herd immunity. “It is certainly between 70 and 80 percent, there is no exact number yet, as we are only investigating the transmission dynamics of the new variant. Of course, a more contagious virus makes everything more difficult. “
The new estimates are at 70 percent or more
Anthony Fauci.
This is also the opinion of Kate O’Brian, Director of the WHO Immunization and Vaccination Department. She told the New York Times in late December that the estimate of 60 to 70 percent is now too low, but no one knows what level of vaccination is needed. “We should say that we just don’t know. And it would not be a valid number for the whole world or for an entire country. “
US state immunologist Anthony Fauci said he is now assuming a necessary immunity of up to 85 percent. One thing is clear: the higher the number, the more people who want to get vaccinated are needed.
Dale Fischer, an infectious disease specialist at the WHO, told Reuters last week: “The virus can be controlled. But we will not be back to normal anytime soon. ”Collective immunities will be needed in most countries to lift border controls and this will not be achieved in 2021.
