The politicization of epidemiological data is inevitable. Government incentives to alter infection, death and hospitalization rates, and ‘load the dice’ in favor of particular outcomes have been a theme during the Covid-19 pandemic. Whether due to reputational concerns of shedding a positive light on the effectiveness of governmental responses, or more concretely to avoid imposing unpopular restrictive public health measures, public health officials are not immune from political calculus. To the contrary, the World Health Organization (WHO) has affirmed that the level of acceptance by the population of pandemic response measures restricting individual liberties should be added as a component of any policy adoption. Of course, beyond the question of whether these elements should be taken into account, hides the trickier one of how. For the latter, no conclusive answers exist.

Generally, though certainly not always, national public health authorities are in a privileged position to collect and disseminate epidemiological data. But this certainly does not mean that they will always do so in good faith. A key challenge in the field of national (and, actually, global) epidemiological surveillance lies in cross-referencing alternative sources to double-check official data. It is quite possible to suspect and accuse public authorities of playing with the numbers; it is less so to offer parallel estimates that are more accurate than those stemming from the authorities´ direct access to privileged information, which is not always publicly available.

One example of this dynamic has recently occurred in Mexico. As explained in the Mexico Country Report in the Oxford Compendium on National Legal Responses to Covid-19, the federal Secretary of Health exercised, on 13 May 2020, his extraordinary powers under Article 73 XVI of the Mexican Constitution, and enacted a nationwide legal mechanism known as the ‘epidemiological traffic light’ (ETL, in Spanish: semáforo epidemiológico). Put simply, the ETL divides the different epidemiological scenarios in each federal state into four colors: red, orange, yellow, and green. Scenarios will be determined through a methodology involving multiple variables, the most important being infection and hospitalization rates. Every two weeks, the assessment is updated in order to reflect, as accurately as possible, the shifting on-the-ground situation regarding infections and hospitalizations. The federal Department of Health adjusts the traffic light, an action that will determine which measures must be in place at a certain point in time in every state of the country.

Each color of the Mexican ETL leads to a series of public health measures that must be implemented by state- and municipal-level authorities. The red and orange ones, the most restrictive, lead to the suspension of public activities or their considerable limitation, including the closure of non-essential businesses and the strict reduction of persons allowed in both public and private spaces. The yellow one lifts several restrictions, mostly maintaining limitations on gatherings in closed public spaces. The green one, based on minimum infection rates, allows the conduct of all public and private activities, while keeping the requirement to wear a mask on public transport.

The official collection and dissemination of epidemiological data in Mexico is conducted through the National System of Epidemiological Surveillance (SINAVE, in Spanish: Sistema Nacional de Vigilancia Epidemiológica). SINAVE relies on a network of state-level administrative authorities obliged to report to the federal Department of Health on the number of probable, suspected, and confirmed cases of communicable diseases – including Covid-19. In the case of Covid-19, the data fed into the system will allow the federal Department of Health to update the epidemiological traffic light correspondingly.

On paper, the ETL makes sense. It avoids the need to constantly renew the catalogue of public health measures as the epidemiological scenario changes. In turn, it provides both inhabitants and state and municipal authorities with certainty on what type of restrictions need to be introduced, and when. Such certainty allows for planning in advance and accommodating the measures to local contexts. It may also help mitigate the social and economic impact of public health restrictions on persons´ lives. These measures’ onerous social and economic toll cannot be overstated.

The system certainly has tradeoffs, two of which are underscored in this post. First, it does not guarantee a dynamic update of the package of public health measures in case they prove to be insufficient. Since the issuance of the epidemiological traffic light in May 2020 and until August 2021, the list of measures to be implemented at each stage remained the same. In Mexico, national-level restrictions on mobility by way of mandatory stay-at-home orders, colloquially referred to as ‘lockdowns’, have been avoided so far. On the one hand, the decision can be understandable considering the major challenges in implementing such a measure in view of institutional capacities, as well as the adverse social, economic, and even health impacts on addressees. Nevertheless, it is contested whether this was, from a public health perspective, a sound approach. A growing body of research has shown how these measures proved to be successful in stemming the spread of Covid-19 elsewhere. Given how stay-at-home orders were not provided for in the Mexican epidemiological traffic light system, they are fully out of the picture at the federal level. However, state-level authorities may go beyond the federal ground floor. A few state governments, like those of Jalisco and Yucatán, have chosen to do so.

Secondly, the epidemiological traffic system creates a series of distorting incentives for state-level authorities tasked with collecting and furnishing epidemiological data to the SINAVE. Even though it is legally mandatory for authorities to provide accurate data, there is ultimately leeway in choosing which data to report, and how to interpret it. Considering the aforementioned social and economic toll of the most restrictive public health measures, it is safe to assume that state- and local-level authorities have multiple reasons to avoid the red color of the ETL. Elsewhere, an expert statistician from Mexico argued that the ETL´s claim of isolating the collection and assessment of epidemiological data from political bargaining has most likely been an illusion.

Two high-profile disagreements between the federal Department of Health of Mexico and the Government of Mexico City, both ruled by the same political party (MORENA), highlight the recurring spillover of political calculus into the assessment of epidemiological data. On 7 December 2020 and again on 6 August 2021, the federal Department of Health declared that data on infection and hospitalization rates in Mexico City corresponded to the red level of the ETL. In response, the Governor of Mexico City declared, on both occasions, that her Government would not operate under the red color, as her own interpretation of the data corresponded to the orange one. In effect, this avoided the imposition of multiple restrictions, notably the closure of non-essential businesses.

In these two episodes, potential disputes of partisan allegiance are not an explanatory variable. Both the federal and Mexico City governments are ruled by the same political party, MORENA. Of course, this does not discard potential intraparty disagreements. Nevertheless, the divergence in criteria seems to be linked to who will assume the political price of a system leading to the restriction on personal liberties. After all, imposing those measures, especially if they are unpopular, is unlikely to be palatable for the population at large. So far, the Government of Mexico City has twice avoided the imposition of more restrictive measures under the ETL. Despite the abovementioned criticism by analysts, no public outcry followed - most certainly not from the inhabitants of Mexico City, who could avoid longer lasting restrictions to their daily lives.

All of the above shows how the weight of pandemic fatigue is a force to be reckoned with. On 18 August 2021, the ETL was revised and the closure of schools was removed as a mandatory measure even from the red and orange colors. Parents wishing for their children to continue with remote learning have the option to do so. The measure has been supported by international organizations such as the WHO, UNICEF, and UNESCO, though they add that both educators and children should be vaccinated. Both the timing and the logistics of the return to in-person teaching in Mexico, however, has been questioned by teachers´ associations and parents. The return took place during a nationwide third wave of rising infection rates, with numerous schools still unequipped to implement the required sanitary measures such as mandatory mask usage and minimum social distancing.

Takeaways for the Future of Law and Epidemiological Surveillance

It remains to be confirmed whether and how epidemiological data used in the ETL's risk assessments has been manipulated, whether in Mexico City or in any of the other 31 federal states in Mexico. It is not possible to scrutinize to what extent the information provided to SINAVE is fully accurate. Such restraint is not meant to foster a general distrust of official data, but rather to shed light on one of the pervasive challenges in national legal responses to Covid-19: can political incentives to manipulate epidemiological data be overcome? If so, how?

These recent incidents in Mexico raise several questions for global debates. What if national authorities are, indeed, altering the numbers and the actual extent of it cannot be known? What about global epidemiological surveillance, where the WHO is supposed to receive and assess data from 196 national authorities under the International Health Regulations of 2005? Political incentives for data manipulation are bound to be replicated, and possibly even magnified, at the international level.

The upcoming high-level discussions on a new pandemic treaty or another legal instrument will have to tackle the question of how to guarantee accurate global epidemiological surveillance when trust and good faith are simply not enough. Depoliticized systems of information-sharing should not be taken for granted. Instead, understanding the core political drivers of epidemiological data manipulation and, where possible, creating failsafe procedures for cross-referencing official statistics with other sources is apposite. If, indeed, public authorities in Mexico have ever altered their numbers, they most certainly would not be a global outlier.