Today is a day that has been marked on the pandemic calendar for a long time. Finally, just over eight months after the start of the vaccination, we are expected to reach that 70% of immunized people that, at first, it was said that it would grant us the group immunity.
We celebrate it as an achievement and, without a doubt, every vaccine that is administered is. However, continuing to talk about that percentage is somewhat out of date, since it has been known for a long time that, under current circumstances, it will not be enough to achieve the also known as herd immunity.
So what is the correct figure? The truth is that none. But let’s see what the reason is.
What is group immunity?
Before talking about percentages, it is worth remembering what the group immunity. It is known as such the number of people immunized, either naturally or through vaccines, which are considered sufficient to interrupt the chain of infections in an epidemic.
Ideally the vaccine works as a firewall, making it difficult for the virus to circulate.
We must see immunity as a firewall. The virus moves freely from person to person, but when it reaches one who has passed the infection or is vaccinated, ideally it could not pass. Like a fire when it meets a firewall.
It is important to highlight that “ideally”, since we have seen that there are reinfections and that coronavirus vaccines greatly decrease the likelihood of hospitalization or death, but they do not reduce so much the one to be infected in a mild way. Anyway, decreases viral load of infected people and the circulation of the virus becomes more complicated.
At the beginning of the pandemic, with the circumstances and knowledge of that moment, it was calculated that 70% of the population should be immunized to achieve herd immunity. Therefore, it was marked as objective when starting vaccination. But things have changed a lot since then.
Why does it no longer make sense?
Viruses mutate, it is their way of existing. We throw our heads up every time we hear about new mutations, but the truth is that the strange thing would be if they did not. Fortunately, SARS-CoV-2, the cause of COVID-19, is not one of those that mutates the most.
The high contagiousness of the delta variant makes 70% not enough
Since the pandemic began, new variants resulting from these mutations and, unsurprisingly, those that have prospered the most have been the most contagious. Fortunately, the fact that they are more contagious does not mean that they are more serious. In fact, the logical thing is that those that generally cause mild illness will prosper, since people who are very ill do not interact with others and, therefore, infections are reduced.
Now, of all these variants, the one that currently worries the most is the delta variant. It is worrisome for several reasons, but above all because of its contagiousness. At the beginning of the pandemic, there was a lot of talk about R0. This is a parameter that indicates the number of people that a sick person can infect. Logically, the containment measures are aimed at reducing this value as much as possible below 1. At the beginning, the coronavirus had a value that oscillated between 2 and 3. However, it is calculated that for the delta variant there is between 6 and 10.
This is due, among other reasons, to the fact that this variant requires a lower viral load to catch it. Therefore, while vaccines are still very effective in reducing hospitalizations and deaths, their effectiveness in preventing minor infections has decreased somewhat.
That does not mean that they do not work far from it.. In fact, if the latest wave of coronavirus in Spain, for example, did not, it would have been disastrous.
Now, 70% is no longer valid for us. There are not enough firewalls, as this variant sneaks better through the nooks and crannies. Therefore, the percentage of vaccinated people would have to be higher. Some experts indicate that it would be about 90% to achieve group immunity. But it is not possible to know for sure. In addition, we must bear in mind that, at least for the moment, it is not possible to vaccinate those under 12 years of age, so that even by vaccinating the entire population over that age we would reach such high percentages.
This may seem defeatist, but it is not. Percentages are simply not worth obsessing over. Things must get better and better if we do not forget what is most important: vaccinate, vaccinate and vaccinate. And that, of course, we are doing very well.