There are still great unknowns such as how long immunity lasts or if the relaxation of measures can cause an increase in cases in the youngest.

View of the Barceloneta beach in Barcelona, ​​this Saturday.

December 27, 2020 was not just any Sunday. Araceli Rosario Hidalgo, born in 1924 and interned in a residence for the elderly in Guadalajara, received the first vaccine against CoViD-19 administered in Spain. Since then (and until the beginning of April) 10 million doses have been administered. Almost 15% of those over 18 years (6.8 million) have received at least one, and 6.4% (slightly more than 3 million) the full pattern.

Although the Government announces a strong acceleration of vaccination, there are still insufficient figures to control the pandemic. The 4th round of National Seroprevalence Study (ENE-COVID), completed in November 2020, showed that 10% of Spaniards (more than 17% in some Community such as Madrid) had antibodies against SARS-CoV-2 due to having passed the disease. And we all know how hard the third wave started the following month.

We are still far from herd immunity (if herd immunity is possible). Let us remember that, at least for the moment, children and adolescents are excluded from vaccination, that the least developed countries will be slow to be vaccinated (and probably also the poorer groups of the developed countries) and that there is the possibility that animal reservoirs of the virus will remain.

But although vaccination coverage is insufficient for the moment, 3 million people with the full guideline is a lot of people. So many. And they are more every day. What they can and cannot do is an important question. For them, for their families, their colleagues and friends and, also, for the economies of their countries. For all.

What can the vaccinated do?

Although Israel has opened the discos for vaccinated people, and the most advanced countries in vaccination announce the return of good times, there is still a lot of uncertainty to define clearly what the vaccinated could or could not do.

The Center for Disease Control and Prevention (CDC) of the United States are perhaps those who have made recommendations more specific (and optimistic) for fully vaccinated people (two weeks after receiving the second dose or the first in the case of single-dose vaccines).

For the CDC, and starting this month, those vaccinated should continue to wear a mask and keep their distance in public, with people from more than two households or with vulnerable people. They should also avoid poorly ventilated spaces and large gatherings, wear a mask on public transportation (and stations), get tested when returning to the United States, and get tested (and isolate themselves) if they develop symptoms. In addition to following the specific recommendations that may exist in some centers or workplaces.

However, the CDC maintains that the fully vaccinated can be reunited indoors with other fully vaccinated people without a mask or distance, or with unvaccinated people from another home (as long as they are not at risk).

They could also travel without restrictions or tests or quarantines within the United States. They don’t even require proof (unless the host country requires it) to travel to other countries. Although yes to return to the United States: a test at origin and a new test after 3-5 days, but not quarantine.

They also do not require isolation or the realization of tests to those vaccinated with contact with COVID-19 patients (unless they develop symptoms or reside in a collective center).

Undoubtedly they are big changes. And, up to a point, daring. For this reason, many countries observe with interest the results of these de-escalation strategies in vaccinated people in societies not yet fully vaccinated.

Why is relaxation a concern?

We know, from the clinical trials for the authorization of the different vaccines, that vaccination is extraordinarily effective in reducing covid-19 cases symptomatic in all age groups. Even when they get infected, the risk of developing severe covid is much lower.

We also know, from observational studies with real-world data on U.S, United Kingdom e Israel, that actual vaccination preserves effectiveness against asymptomatic covid. And, also, even preliminarily, that those vaccinated who become infected have lower viral loads than the unvaccinated. If a significant proportion of vaccinated people are not infected and those who do have a lower viral load, transmission capacity should decrease noticeably.

No We know for the moment how long it lasts – and, where appropriate, when and how it decays. the protection offered by vaccination (or natural immunity after the infection has passed). At the moment, and considering the humoral and cellular immunity, the protection seems to hold up quite well for at least 6 months. Furthermore, the reported cases of reinfection are anecdotal.

We also know that vaccines perform well for most variants of concern, including the British variant (B.1.1.7). But in the laboratory they lose some effectiveness against the South African variant (B.1.351) and other variants with the E484Y mutation. And we ignore the impact of this partial loss of effectiveness in the real world.

But, and perhaps above all, we do not know the capacity of SARS-CoV-2 – in the more or less immediate future – to evade the immune response produced by vaccines (or natural immunity). Every day that transmission persists – and it is still very high in many countries – you have opportunities to mutate and try. And the future is not written.

In this context of uncertainty, excessive relaxation after vaccination could be problematic. It is of concern, in the first place, that the possible “relaxation” of measures in the vaccinated could lead to an increase in infections between them. Still mostly asymptomatic, and despite their lower transmission capacity, they could be transferred to infections in non-vaccinated people, mainly younger populations (the ones who are late in receiving vaccination).

And although young people (and also those vaccinated) maintain a lower risk of developing severe covid, if the transmission is very high they could lead to a problem of saturation of sanitary services and deterioration of health.

Also of concern is the potential development of escape variants or a decreased immune response leading to reinfections. And, above all, the combined combination of all the risks is of concern: high rates in young, new variants and reinfections.

Prudence should not make us reckless

The alternative of maintaining restrictions for those vaccinated also has significant social costs. In social distance, in loneliness, in pandemic fatigue, in delayed recovery and in increasing poverty. Prudence on the one hand should not make us reckless on the other. Decisions will have to be made balancing risks and benefits at all times.

Exists much uncertainty and the recommendations will change as vaccination progresses and new scientific evidence becomes available on its impact on transmission.

The reasonable thing is to follow the rules established by the health authorities at all times (not following them could lead to sanctions). Nowadays in Spain the recommendations do not establish differences between vaccinated and unvaccinated. Nor in other countries with the most advanced vaccination campaign, like the UK.

It is also reasonable that these recommendations be updated as soon as possible, with the advance in the number of people vaccinated and with the new evidence on the impact of vaccination on transmission (including what we learn from countries that have already begun to relax measures). And without fear of backtracking if the epidemiological situation advises it.

In this we must also combine impatience in the search for normality and recovery with patience to be able to reach them without more sacrifices than we are forced to make. It will not be easy to find a balance. And we will make mistakes. More mistakes. By default and by excess. But we have known for a long time that it is not easy to make decisions in these times.

Finally, it should be remembered that it also worries (and a lot) relaxation in the immediate weeks after the first dose, when our body has not yet had time to produce antibodies against SARS-CoV-2 and we still do not have protection. Here we do know that we must maintain all the same measures as those not vaccinated. In this we do not have the slightest doubt or uncertainty.

* This article was originally published on The Conversation.

** Salvador Peiró is a researcher, Health Services Research Area, FISABIO SALUD PÚBLICA, Fisabio.