Beijing time July 16 news, according tomedia reports, we have defeated smallpox and polio, the new crown pneumonia (also known as “2019 coronavirus disease”, abbreviated coVID-19) will become the next? Group immunity is the ability of a group to be sufficiently immune to a disease to prevent the spread of the disease. Researchers at the University of Manchester first coined the term in 1923 to describe how a group of subjects (mice in the study at the time) developed immunity to a disease when not all individuals were vaccinated.
Widespread vaccination is the most reliable way to achieve mass immunization. The whole concept of mass immunity raises the question: How many people do you need to vaccinate in the population to eradicate a disease?
However, the actual implementation of mass immunity is often much more complex and not always achievable, especially with viruses that are not yet vaccinated, such as the new coronavirus that causes new coronary pneumonia, and which involves a number of factors beyond the virus itself.
How to measure group immunity?
It is relatively simple to calculate the number of people who are immune to a disease, i.e. no longer continue to be infected. First, scientists want to determine the pathogen’s R0 (read R-nought), the basic number of infections. This is a variable that estimates the average number of infections that an infectious individual will infect based on the inherent characteristics of the pathogen. It is worth noting that R0 is not static. A more precise figure is Rt (effective infection), which refers to the number of infections that change with the development of the outbreak and over time, based on the number of basic infections, such as the expected number of cases in which an infected person transmits the disease to another person after the adoption of epidemic prevention measures. However, in order to calculate the threshold required for group immunization, epidemiologists start with R0.
The 2014 outbreak of the Ebola virus had a R0 of about 2, meaning that one patient infected with the virus was infected with an average of two other patients. For measles, R0 is close to 15. Although R0 of the new coronavirus is not yet available, the researchers estimate that the value is about 3.
The R0 value for some infectious diseases may seem low, but as long as it is just over 1, it can still get out of control quickly. If we assume that R0 for the new crown pneumonia is 3, this means that each case will eventually result in three minor cases, 1, 3, 9, 27, and so on.
The key to achieving mass immunization is to turn the disease R0 (Rt if up-to-date) into 1. When individuals become immune to pathogens by vaccination, or by recovering from disease, the number of people who may be infected in the population is decreasing. For measles (R0 – 15), group immunity is achieved when 14 out of 15 people, or about 93% of individuals, are immune. For new coronal pneumonia, about two-thirds (about 66%) of people have immunity may be enough.
How is it achieved mass immunity?
When scientists talk about group immunization, it’s almost always in the context of vaccines. “Group immunization will be the main goal of the (New Crown Pneumonia) vaccine program,” said Danny Altmann, professor of immunology at Imperial College London, “which is why it is necessary to evaluate and compare candidate vaccines calmly and objectively.” We need vaccines that are immune-to-etusional (immune-to-reaction) that are protective, safe, and capable of producing a sustained response. “
However, there is another way to obtain group immunity. If it is an infection of pathogens that cause lifelong immunity and the spread of the disease is not controlled, the infection rate will multiply and then naturally flatten and decrease, and as more and more people become infected with the disease, recover and gain immunity, and eventually achieve mass immunity. There is no vaccine intervention in this process.
However, this approach is not reliable for two reasons.
First, the method only works in a relatively closed population, and there are not enough individuals in the population who have not been exposed to the pathogen to host it. However, even isolated communities cannot completely avoid this risk, as children are not born immune and many diseases disappear due to the presence of the group’s immune system, but these diseases continue to spread as enough newborns enter the population.
Second, acquired group immunity for sexually transmitted infections occurs only when a sufficient proportion of the population actually is infected with the disease. This is not an undeniable conclusion, but based on preliminary data from the European countries affected by the outbreak, and a Spanish study published in The Lancet in July 2020, it is almost certain that the case will not happen. Epidemic data show that, despite the heavy losses, the new coronavirus has infected only a small part of the population – well below the threshold for group immunization. Sweden has many cases of infection, many deaths, but not meta-immunisation. Spain and Italy also did not achieve group immunization, and the survey found that the immunization rate in those countries may be 15 per cent.
Although many believe that once patients recover from neo-coronary pneumonia, they will be immune to future infections, but studies increasingly suggest that may not be the case.
“We see people having ‘new crown parties’ and they think ‘I’m going to go, get infected, and then it’s all right,'” Hunt added. “
Group immunity is not always effective
Scientists already have a clear idea of how to achieve natural group immunity. What you’re asking for is a disease that guarantees strong immunity, is largely asymptomatic, and has a lower R0. However, even if R0 is relatively high and most patients have symptoms of the disease, it is still possible to achieve mass immunization through effective vaccines and vaccine programs. Think of our big, successful public health cases, such as smallpox and polio. Their eradication is entirely due to ongoing mass vaccination programmes and simple and efficient vaccines.
For group immunity, a strong immune system is necessary to ensure that those who are immune stay long enough for the pathogen to disappear, and asymptomatic transmission is also helpful, because it means that fewer people may die as people wait for the group’s immunity to form, and that enough survivors first affect the probability of group immunity success. Of course, lower R0 lowers the threshold for the number of people with immunity, so we can see a leveling and decreasing infection rate.
Still, some diseases that appear to be likely to form mass immunity have never really achieved this goal. For example, despite widespread infections and vaccinations, chickenpox has never been completely eradicated from the world’s population. This is because the virus that causes chickenpox lurks in the nerve roots of infected people even after they recover and gain immunity. Once infected people age, their immune system weakens, and the virus can reactivate and cause shingles, which in turn can cause chickenpox.
In a small island community, you may try to get rid of chickenpox, but in the weeks after someone’s grandmother develops shingles, every child on the island gets chickenpox, the community has gained group immunity, and the virus has disappeared, but in fact it’s still waiting for an outbreak. The World Health Organization says a similar phenomenon is happening in tuberculosis.
If the vaccine produces only a short-lived immunity in the population, then the vaccine-induced mass immunity also fails. In the case of pertussis and mumps, it has recently re-emerged after it was widely believed that the vaccine programme had eradicated these diseases for a long time. Studies have shown that, despite vaccine non-compliance, these outbreaks are partly due to vaccine ineffectiveness over time. Over the past few years, both pertussis and mumps have erupted, mainly due to a gradual decline in vaccine immunity.
Is it possible for new coronary pneumonia to obtain group immunity?
With an effective vaccine, it is possible to achieve mass immunization and end the new coronapneumonia pandemic. However, we may have to have regular follow-up vaccinations, as early data from rehabilitated patients suggest that the new coronavirus provides only a few months or years of immunity.
We know that people with atypical pneumonia (SARS), MERS, and seasonal coronavirus do not detect antibodies two or three years after infection, so it is not surprising that the idea of getting permanent immunity by vaccination, like a vaccine for measles, rubella, smallpox or polio, is incorrect in the current situation.
On the other hand, however, without a vaccine, the likelihood of natural group immunity from neo-coronapneumonia would be very low, as the infection rate would not even be close to the percentage required to reduce R0 to 1. It may take months or years for us to reach this threshold, and by then many people who have been infected with the disease may lose their immunity, creating the conditions for a recurrence and another cycle of disease and loss.
It is thought-provoking that even though neo-coronary pneumonia may naturally form group immunity, the damage in this process will be far greater than we thought. You may have to endure such a terrible epidemic that will destroy social infrastructure and cause a large number of deaths, but still lack mass immunization. (Any day)