The Covid-19 vaccination campaign started in Spain, and in most European countries, on 27 December 2020. From the start of the campaign, priority was given to injections for the elderly, and as the campaign progressed it was extended to other age groups. Eight months later, at the beginning of September 2021, 72% of Spain’s population had already been vaccinated.

In Spain we have carried out a rapid and very well-organised vaccination campaign by age, which has allowed usto protect the most vulnerable element: the elderly. In early July we vaccinated more than half a million people a day. The benefits of mass vaccination by age have been evident in the fifth wave in terms of reduced severe disease and fewer deaths from Covid-19.

The success of the vaccination campaign in Spain has been largely due to the strength of the National Health System and its implementation through primary health care. This is a fundamental differentiating factor compared to other major European countries.

Going for herd immunity

Given the success of vaccination, we must not lose sight of the fundamental objective, which is to achieve herd immunity.

The epidemiological definition of herd immunity according to the US Centers for Disease Control and Prevention (CDC) is: “A situation in which a sufficient proportion of the population is immune to an infectious disease (through vaccination and/or previous illness) to make its spread from person to person unlikely. Even individuals not vaccinated […] are offered some protection because the disease has little opportunity to spread within the community.”

Therefore, the next mandatory question is when we will reach herd immunity. According to the WHO: “The proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known. This is an important area of research and will likely vary by community, the vaccine, the populations prioritised for vaccinationand other factors.”

It is clear that the goal is not a high percentage of vaccinated people, which figure we have not been able to establish, but the point at which we see a dramatic decrease in infections in the population. Then we will reach herd immunity and for that, now more than ever, we need to continue vaccinating and monitoring infections.

Right now in Spain, and in all the countries that have been able to reach high levels of vaccination in their populations, it is essential to determine and reach the population that has yet to be vaccinated. With the viral variants we have and those that may arrive, it is likely that we need to vaccinate practically all of our populations. To do this, it is essential to identify that 28% of the Spanish population, to know about those who are lagging behind invaccination: who they are and how to give them the necessary doses. Identifying and knowing this 28% leads us directly to studying the inequalities in vaccination that persist and which in many cases we are unaware of.

Inequality in the pandemic

Inequality in the face of Covid-19 has been a constant throughout the pandemic. Since its inception, we have seen how the disease burden of Covid-19 and its consequences were not equal for all the people who make up our societies, our cities, our countries.

As early as during the national lockdown in March 2020, we wondered whether all sectors of our population could face this public health crisis with the same guarantees. And we were soon able to see how global cities, characterised by enormous inequality and great social and spatial segregation, showed up to three times more disease burden in disadvantaged neighbourhoods than in those with more resources.

Now, in September 2021 and entering the second autumn of the pandemic, we are in the phase where mass vaccination plans have reached most of the population in wealthy cities and countries.

What is interesting about vaccination campaigns is that we expected, once again, that they would be equally effective for all people and social groups. And once again we see that they are not, that what we call the social gradient of health and disease is also confirmed in vaccination campaigns. For weeks now we have been seeing analyses and publications showing inequalities in vaccination processes in different countries and regions.

In the USA and the UK, where the study of inequalitiesin public health is very advanced compared to other countries such as Spain, wefind different studies in this regard.

In the UK, several studies (such as this one from November 2020 and this one from May 2021) have focused on a reluctance to be vaccinated, which was shown to be higher in minority ethnic groups and people on low incomes who had also been disproportionately affected by Covid-19.

A similar study carried out in Texas on vaccination showed how men of Mexican origin asked for more accurate information about vaccines in media they would listen to, the accessibility of vaccination sites and the potential financial cost of vaccines. The Biden administration is committed to distributing vaccines equitably to the communities most affected by thepandemic.

The CDC ranks counties according to the Social Vulnerability Index, an indicator used in public health crises that is based on socioeconomic status, housing, transportation, race, ethnicity and language. Most of the most disadvantaged municipalities with the fewest fully vaccinated people are in the south, while the most vaccinated and least vulnerable municipalities are in the Midwest and Northeast.

Not just denialists

And to return to Spain, a huge effort is being made in Catalonia to monitor and act on vaccination inequality to identify those people who are lagging behind and need to be protected.

Epidemiologist Carme Borrell has said: “In Barcelona we have observed that there are significant inequalities in the vaccinated population in different areas ofthe city. Areas with a lower socio-economic level have had lower coverage of up to 30 percentage points. To alleviate these inequalities, various actions have been taken, including the establishment of 24 face-to-face support points tomake appointments for vaccination in neighbourhoods with lower percentages of vaccinated population.”

The processes of inequality in relation to vaccinationare complex and are influenced by various factors: the digital breach, migratory status, language, culture,and scepticism towards vaccines.

From a scientific point of view, we are faced with the problem of studying those who do not get vaccinated and determining the unvaccinated population in detail. This is of great interest to us to arrive atherd immunity.

The study of inequalities in vaccination is complex and requires an in-depth study that is always accompanied by community health actions with a clear focus on equity.

Next steps: bringing vaccination closer to those who are left behind

Whenever it has been possible to establish those people who are lagging behind in vaccination, it has been observed that they are not only those who actively refuse vaccination; rather, there are many cultural, linguistic and occupational aspects that play a role when it comes togetting vaccinated.  Many informal workers were afraid of losing days of work due to the adverse effects of the vaccine, a fear of losing their jobs.

The effort to open hospitals and vaccination centres 24 hours a day is massively onerous and very costly. Setting up vaccination posts in neighbourhoods, industrial estates, at times when it is easy for people who have not yet been vaccinated to attend, must be part of the strategy from now on. And let us remember that, with every passing day, it is becoming more important to reach the entire population. It is key to be able to offer vaccines to the 28% that will become increasingly difficult to reach.

Now that vaccination is reaching a huge part of our population, we need to contribute scientific evidence, knowledge, and action to ensure that all people have access to vaccines. This is the way to get see a steady and controlled decline in infections as soon as possible, to attain the desirable herd immunity.

Manuel Franco is Professor of Epidemiology at the University of Alcalá in Madrid and the Johns Hopkins School of Public Health (USA).