Immunity as a riddle

It was initially said that the crown march would be stopped when 60 to 70 percent of the population was vaccinated, but now that percentage is rising to 80

As much as our citizens were annoyed by the announcements of the medical part of the Crisis Staff for the suppression of the pandemic that the next two weeks are crucial in the fight against the corona, it is now confusing that their chief epidemiologist is gradually increasing the percentage of vaccinated population needed to provide the nation with collective immunity. When 60 to 70 percent of the population is vaccinated or gets over covid, the virus will be stopped, epidemiologists said at the beginning. The World Health Organization continues to cite that range, but most other epidemiologists are quietly moving that percentage up.
People around the world are aware that it is impossible to know with certainty what limit the collective immunity needs to reach in order to breathe freely again, but everyone would be calmer with a good assessment. And, for now, no!

Interest for the vaccine

A month ago it was said that it was enough for 70 to 75 percent of the population to be vaccinated to create collective immunity, last week it was said that it was between 75 and 80 percent, and even more. It is possible that with this truth he hesitated to come to light, because it seemed to that many were hesitant to receive the vaccine, but when the first interest in the first vaccines was seen (at least in some countries), they decided not to hide that the return to normalcy could take longer than expected.

Now we can hear some comparisons of covids with smallpox. And that is that it will take immunization of close to 90 percent of the population to stop the virus, almost as much as it takes to stop smallpox (measles).

We remind you that measles is the most contagious disease in the world: the virus can survive in the air in one room for hours and infect anyone who is in it, but has not been vaccinated. Some studies have found that when an epidemic of smallpox breaks out in a crowded military barracks and dormitory, the virus is transmitted until more than 95 percent of residents are infected. Such scenarios are stopped only by the collective immune wall, ie. sufficient number of vaccinated.

Well-known epidemiologists are ready to agree with this announcement, because earlier predictions that 60 to 70 percent would be enough were undoubtedly too optimistic: the virus is transmitted more easily and faster, so stronger collective immunity will be needed to stop it. They warn that these are just assumptions, no one can know the exact numbers.

Later findings became much more important than the original ones from Italy and Wuhan, first that when it comes to the corona virus, there are asymptomatic cases and examples of supertransmitters: when only one person infects dozens of others. Experts warn that at mass gatherings, such as parties, sports matches or theater performances, where no one wears masks, the mentioned reproductive number can increase to 4, 5 or even 6. In such places, the collective immunity must be at least 80 percent. to slow the spread of the virus.

Scientists agree that another detail complicates the story with collective immunity: the virus itself is more transmitted, to a larger number of people. The "Italian strain" with the mutation known as D614G spread much faster than the original Wuhan variant. Recently, a new strain (also called N501Y) was identified, first in Britain and South Africa, and then quickly spread around the world. The more transmissible the pathogen, the more people must become immune to stop it.

How dangerous is one infected The first assumptions that 60 to 70 percent of the immunized population would be a sufficient "shield" were based on early data from China and Italy. Subsequent epidemiological monitoring of how much the number of people infected with the corona virus doubled or tripled a new light on the reproductive number, which is denoted by R0. It determines the average number of people to whom the infection is transmitted by one infected person in the susceptible population, and it is three.

So, two out of three potential victims would have to be immune (if they have been vaccinated or have already contracted covid) for an infected person to infect only one, because then the infection subsides. When one infected person infects two more with the corona, the percentage of collective immunity that would stop it should be 66.7 percent (thus reaching the range of 60 to 70 percent).

The study of French military doctors, who studied what happened to the crew members of the "Charles de Gaulle" aircraft carrier at the end of March, which became the focus of the corn virus, also helps in understanding this number. It was determined that 1,064 out of 1,568 sailors on board had a positive test, or about 68 percent, but the study also has shortcomings. Among others, life on a ship is quite different from the free movement of people on land.

It is easy to measure in a herd

The only really accurate measures of collective immunity are obtained in real herds (hence the phrase herd immunity) and come from the study of infectious diseases in animals.

- When cattle are in a barn or barn, it is easy to measure how fast the disease spreads from one animal to another. People move, so studying the spread of the disease among them is much more difficult.