Every day we hear that vaccines are decreasing COVID cases, hospitalizations and mortality. The Government of Spain assures us that before summer we will have 70% of Spaniards vaccinated. In a few days the alarm state will disappear. We can think that this nightmare is over, that this summer we will wear our entire brown face, without the pallor of the mask. Party and travel without restrictions. But can we be so optimistic?
The vaccine will be a tool for containing the virus and therefore the pandemic, but associated with physical or social distancing measures.
What does it take to cut the transmission of the virus?
For viruses to be transmitted, several things are needed, and each one of them facilitates, or hinders, their transmission. The first is the ability of the virus to spread from person to person. There are viruses, such as measles, which are transmitted with astonishing ease. Other viruses are not as skilled at transmitting and therefore infect less.
Another very important factor is the contact between the infected person and others. The more contact, the easier it is for the virus to spread to others. A hermit, for example, is very difficult to be infected by respiratory transmission virus, since he does not have contact with infected people.
The third important point is the ability of contacts to become infected. Thus, an adult does not get measles even if he comes into contact with an infected child because the disease has passed or was vaccinated in his day.
All this is what the effective R0 measures – about which we will have read or heard in the news. This number indicates the number of infections that an infected subject will cause. It is also a changing number depending on social interactions and the immune status of the population.
Imagine that you are a supercontagator, that is, that you have a great capacity to infect those around you. It will infect less if you are on the Malvarrosa beach than in a nightclub, if you wear a mask than if you do not, or if you work in an office or open plan office. It will also depend on whether the person with whom you have contact can be infected. If the disease has already passed, it is very difficult for it to be infected again, so its contagion capacity will decrease.
Vaccines have been shown to be more than 80% effective in preventing severe COVID cases and mortality. But they also prevent infection. Those vaccinated are less likely to become infected and therefore to transmit the infection, but measuring by how much it does so is difficult. What is clear is that the more people vaccinated, the more difficult it is for the virus to be transmitted.
What proportion of the population must be vaccinated for the virus to stop being transmitted?
At the beginning of the pandemic, it was estimated that when 60-70% of the population were protected (either by the vaccine or by having already passed the infection) it could return to normality (group immunity is achieved). Hence, there is talk of 70% of those vaccinated.
Today there are doubts about it. Aspects such as the protection of the vaccine to avoid infection, the slow development of vaccination programs, the lack of knowledge of the duration of protection by the vaccine and the appearance of new strains mean that this number is rising to almost 80- 85%.
To achieve good group immunity, vaccination must include all ages and regions. With news about vaccine safety, you can lose confidence in them. The youngest, with a lower incidence of serious diseases, may become reluctant to get vaccinated.
Also the delay in the vaccination of children can delay us that expected group immunity. Furthermore, countries, even continents, are not islands, and viruses do not understand borders. So it is also important to achieve high coverage in developing countries.
Living with caution
With all this, we have to hope that SARS-CoV-2 has come to stay with us, and until the virus and we ‘adapt to living together’, precautions will have to be maintained. Relaxation of virus containment measures can lead to increases in disease. It is important, in this containment of the disease, to always go ahead.
Mathematical models show that the delays in the adoption of control measures explain why in some countries the pandemic has affected more than in others. It is crucial to isolate the virus, that it has the fewest opportunities to spread among us.
Therefore, the vaccine will be a tool in the prevention of infection, but for the moment always allied to physical distancing through the use of masks and contact restrictions.
Javier Díez, Head of the Vaccine Research Area, Fisabio
This article was originally published on The Conversation. Read the original.
