Rodrigo has a severe immunodeficiency. What does this mean? That he was born with incomplete defenses. You have inherited altered immune genes. This allows you to defend very poorly against some infections, to the point that you could die.
Olivia, however, has a very severe allergy to gelatin. If you eat it (no matter how small the amount) or come into contact with it, you suffer from severe allergic reactions. An anaphylactic reaction (hives, blood pressure drop, respiratory compromise, and digestive problems) could lead to death from anaphylactic shock if not acted on quickly.
We cannot administer the MMR vaccine to Rodrigo and Olivia (it contains attenuated measles, rubella and mumps viruses). Him, because live viruses could cause deadly infection. To her, because this vaccine contains gelatin and could cause a serious allergic reaction.
Are they both condemned to suffer from measles and its possible serious or fatal consequences? Not fortunately. If they live in a community that is vaccinated against measles (colleagues, neighbors, relatives, friends, etc …) they will be protected by this environment. We can say that being in the herd has a great immune advantage.
Advantages of achieving herd immunity
The rate that estimates the speed of transmission of an infection is known as R₀ (basic reproductive number). It is not the only epidemiological factor to monitor a pandemic, but it is one of the most relevant.
This indicator gives an idea of how contagious a microbe is. In the case of measles, the R₀ can reach 18 (each patient could infect 18 people). In the case of covid-19, this rate is much lower (around 3).
The so-called ‘herd immunity’, also called herd or group immunity, is calculated from the transmission speed value. It is the protection of a certain population against infection due to the presence of a high percentage of individuals immune to it.
This immunity can be achieved in two ways: naturally (infection) or artificially (vaccination). They both count and add.
The model for calculating the necessary percentage that we need to have protective group immunity of the entire herd is: (1 – 1 / R₀) x 100. That is, for measles (R₀ = 18) if we do the math, the immunity of flock is achieved with 95% of immunized people.
On the other hand, for SARS-CoV2 (R₀ = 3) we need only 66%. So Rodrigo and Olivia, who cannot be vaccinated against measles, would be protected if we had more than 95% of society vaccinated. And so it happens, because in Spain we have a great vaccination coverage for MMR.
When can we get back to normal?
At present, and according to data from the fourth wave of the seroprevalence study, 10% of Spaniards would be immunized after having passed the infection.
We know that this data is an indicator of minimums. It does not include people who have overcome covid-19 and have other antibodies or those who have only cell memory. But the number is – in any case – far from the 66% needed to achieve group immunity.
We cannot let our guard down. We are more than 7.8 billion people in the world and the vaccination strategy should be global, not national. We need more than 5.1 billion vaccines (more than 10 billion doses because many of them require two doses). So we have many months ahead of us.
Next to this, there is an even more important piece of information. We know that with the first available vaccines (based on the new technology of using messenger RNA) the vaccinated are immunized against a possible infection by SARS-CoV2.
But there are doubts as to whether it can totally stop the contagion. That is, in those vaccinated, the virus could still grow in their respiratory tract and spread. The scientific publication of Pfizer’s results raises this question, which is still pending today.
Therefore, as long as there are no “sterilizing” vaccines (which, in addition to protecting, stop the contagion) or we do not have 2 out of 3 immunized people, social behavior should be as it has been until now. We will have to continue with prevention and hygiene measures: Use of masks, frequent hand hygiene, physical distance of 1.5 meters and effective ventilation in closed spaces.
These measures are expected to be initially relaxed outdoors. When we have herd immunity we will begin to look at the new normal. These measures are here to stay, just like the virus. Just as the AIDS pandemic changed condom use habits forever.
New variants of the virus
Viruses (and this is no exception) existentially mutate. Not to make themselves worse but because there are many millions of organisms in continuous growth.
Viruses use an enzymatic system to copy their genetic material that makes many mistakes (mutations). These failures almost always make the new virus non-viable and disappear.
But there are so many that, by chance, some of these failures survive. There are more than 275,000 recorded variations in the SARS-CoV-2 sequence record. So this modus operandi is not new.
What is new is that the variant found in the United Kingdom, under investigation, accumulates 29 mutations. Many of them affect the code that prepares the S protein, or “key” for the virus to enter our cells. So far, it has not been detected that this variant (nor the most recent South African) is more harmful or has a worse evolution.
What is suspected is a faster transmission. So we have to increase surveillance in all countries and control whether we have this variant among us as well as the evolution of the disease: there are already cases in Spain, France, Italy and Japan.
To our peace of mind, the first vaccines have already been shown to remain effective. Antibodies that are generated after vaccination (directed against protein S) also recognize and neutralize new variants of the virus.
You have to remain firm and not lower your guard. If there were large variations in the virus, we could improve and adapt the vaccination strategy (against a mixture of strains or lineages, as with other viruses).
The goal is to continue with this strategy and achieve 70% social immunity. Thus, people with serious diseases can benefit from herd immunity. Get vaccinated, vaccinate them!
Alfredo Corell Almuzara, Professor of Immunology, University of Valladolid
This article was originally published on The Conversation. Read the original.
