It depends on me

 

 

 

Much has been said about the impact of vaccines, probably also mixing hopes and predictions. An editorial in the March issue of the prestigious scientific journal Nature summarizes five reasons why reaching herd immunity for Covid-19 is unlikely.

 

The first reason, according to the author, concerns the effectiveness of vaccines: it is not yet clear whether these reduce the chances of transmission of the virus. To achieve herd immunity, the threshold of which has been estimated at around 60-70% of vaccinated population, it is necessary to be sure that those who have been vaccinated or have already contracted the virus cannot transmit it to others. The vaccines developed by Moderna and Pfizer-BioNTech, for example, are effective for symptomatic disease, but it is not entirely clear whether they are also effective for limiting its transmission.

 

The second reason identified by the author lies in the geographical disparities with which the vaccine is administered. For example, while Israel is currently the world leader in percentage of vaccinated population, thus approaching herd immunity, other countries such as South Africa and Israel's neighbors are still a long way from this target. National averages also mask huge internal disparities in vaccine administration. We live in an extremely interconnected world and no man is an island: the onset of outbreaks, even if herd immunity is achieved, is therefore not to be excluded if the administration of vaccines continues in such a different way. In other words, even if almost all of them are vaccinated in my country, the risk of outbreaks cannot be ruled out if the same vaccination coverage is not achieved in neighboring countries.

 

The third reason concerns the new variants, potentially more transmissible, against which current vaccination efforts could lose effectiveness. The more time passes to vaccinate at least 70% of the population, the more time the virus has to mutate and infect not only the remaining population, but also those who have already received the vaccine.

 

The fourth reason, the author argues, citing epidemiological studies, is that immunity does not last forever, but tends to fade over time. How long the vaccine lasts is still unclear. If it lasted only for a few months, this would constitute a very tight deadline for the administration of vaccines in order to achieve herd immunity.

 

The last reason, the most interesting from my point of view, concerns the interaction between vaccine administration and human behavior. Without vaccine, through lockdown periods we have managed to keep the contagion curve under control in some crucial phases. However, the more people who are vaccinated, the more - reasonably, I would say - social interactions will increase, altering the mass immunity equation which is also based on the number of people exposed to the virus. Considering the insufficient efficacy of the vaccine and the incomplete coverage of the population, an increase in social interactions after the vaccine could limit the effects of the vaccination campaign and keep us away from herd immunity.

 

In fact, the vaccine does not in itself act as a magic wand to eradicate the virus from the planet. Probably, rather than achieving herd immunity, it is more reasonable to imagine a normality in which we will live with the virus as we have done so far with seasonal flu. Therefore, individual behaviors remain a crucial factor in allowing the vaccine to reach its maximum effectiveness. While, on the one hand, the spread of vaccines can ease the hospital overload related to hospitalizations, individual responsibility, on the other hand, remains an important pillar for limiting outbreaks even in the case of herd immunity. Achieving the latter does not tell us that we are finally free from the virus, but it suggests that we can be a little more relaxed. But if we want to arrive prepared for the "new normal", precautionary behaviors such as social distancing and use of the mask still seem to be necessary, both in these early stages of vaccine administration and to achieve the hoped-for herd immunity.