The country was certified by the Pan American Health Organization as having eliminated endemic measles transmission in 2016. The achievement was reversed three years later, after the virus returned and spread across the country. In November 2024, Brazil regained its certification, a reminder of both the strength of its public health system and the fragility of that achievement.
In São Paulo state, 23 measles cases have been confirmed in 2026, compared with just two throughout 2025. Twenty of those cases are in the city of São Paulo, with additional infections reported in São Bernardo do Campo and Guarulhos. The increase prompted health authorities to recommend measles vaccination for everyone between six months and 59 years old in the three municipalities, regardless of previous vaccination history.
The numbers are still small compared with the major outbreaks that once swept through Brazil. But measles is an unforgiving indicator of weaknesses in collective immunity. The virus is among the most contagious infectious diseases, and when vaccination coverage falls below the level needed to interrupt transmission, a single imported infection can find a population increasingly vulnerable to it.
THE warning was already there
Brazil’s vaccination crisis did not begin with Covid-19. Childhood vaccination coverage had been declining for years, with a particularly sharp deterioration after 2015. According to the VacinaBR yearbook, produced by the Instituto Questão de Ciência with support from the Brazilian Society of Pediatrics and Immunization and in partnership with UNICEF, the decline affected vaccines across the childhood immunization schedule. Although coverage began to recover in 2022 and improved significantly in 2023, no childhood vaccine reached the national target in every Brazilian state that year.
Measles illustrates the problem particularly well. The WHO and UNICEF estimate that Brazil’s coverage for the first measles-containing vaccine dose fell from 97% in 2014 to 73% in 2021, before recovering to 90% in 2023, 96% in 2024 and then falling again to 90% in 2025.
The target matters because measles leaves little room for complacency. A coverage rate of around 95% is generally considered necessary to maintain the level of collective protection required to prevent sustained transmission.
The Brazilian Federal Council of Medicine made precisely this warning in late 2025, arguing that national vaccination coverage had remained around 85% for several important vaccines, well below the 95% target.
The problem is not simply that people stopped believing in vaccines, but that vaccines became less visible precisely because they worked.
When a generation grows up without seeing children hospitalized or dying from measles, polio or meningitis, the diseases become abstract. The vaccine, meanwhile, remains tangible: an injection, a possible side effect, a decision that requires trust. The success of immunization can therefore create its own paradox. The better vaccination works, the easier it becomes to forget why vaccination is necessary.
What changed during covid?
All over the world, vaccination was no longer simply a public-health measure. It became intertwined with arguments about government authority, individual freedom, science, institutions and political identity. In Brazil, this was particularly visible during Jair Bolsonaro’s presidency, as he frequently advocated for “freedom,” opposed mandatory vaccination and promoted alternative approaches to dealing with the pandemic.
Research published in Frontiers in Political Science found that political preferences were strongly associated with with differences in Brazilians’ knowledge about and misinformation surrounding Covid-19. The study concluded that supporters of Jair Bolsonaro were more likely to accept misinformation and conspiracy theories about the virus in the context of a government that repeatedly downplayed the risks of the pandemic. (Frontiers)
The same political divide appeared in vaccination itself. An ecological study of Brazilian municipalities found an association between support for Bolsonaro and lower Covid-19 vaccination uptake, even after adjustments for socioeconomic and demographic characteristics. The researchers described the politicization of vaccination as a new challenge for immunization programs.
The political environment was not merely theoretical. During the pandemic, Bolsonaro repeatedly questioned the effectiveness and safety of Covid vaccines. In June 2021, for example, he incorrectly described the vaccines then being administered in Brazil as still being in an “experimental” stage, despite regulatory authorization and clinical evidence supporting their use.
He also repeatedly questioned the need for vaccination and said he would decide whether to take a vaccine only after the rest of the Brazilian population had been vaccinated.
These statements mattered not simply because they came from a president, but because political leaders can provide what researchers call informational cues: signals that help people interpret complicated issues for which they may not have the technical knowledge to evaluate the evidence themselves. The result was a new kind of vaccine debate, one in which scientific evidence could become secondary to political allegiance.
From public health to political identity
This transformation is visible online.
A study examining more than one million tweets and four million retweets during the Bolsonaro administration identified clearly divided pro- and anti-vaccine communities. Researchers found that anti-vaccine actors were particularly successful at framing the discussion around Covid-19 through populist, anti-science and anti-establishment narratives.
Another Brazilian study examining vaccine misinformation found that false information about Covid-19 vaccines became strongly connected to the country’s political polarization. Social media platforms including Instagram, Facebook, Twitter and WhatsApp played an important role in disseminating those claims.
That does not mean that every person who hesitates over a vaccine is politically motivated. Vaccine hesitancy has many causes: fear of side effects, lack of information, distrust in institutions, difficulties accessing health services, complacency and simple forgetfulness. But it is clear that, for some groups, vaccination became a way of expressing their distrust in the health system.
The post-pandemic inheritance
A national survey reported by Rádio Senado in June 2026 found that 72.1% of respondents said they kept their vaccinations up to date. But 9.9% said they did not get vaccinated at all, while another 9.2% said they had stopped vaccination during the Covid-19 pandemic. Among 16-to-24-year-olds, only 62.9% reported keeping their vaccinations up to date; among people aged 25 to 34, the figure was 62%.
The survey’s coordinator, researcher Pedro Arantes of the Federal University of São Paulo, linked part of this decline to misinformation generated during the pandemic and to a loss of perceived risk.
The problem today may not be a country suddenly converted to anti-vaccine ideology. It may be a population whose relationship with vaccination has become more complicated: less automatic, less institutional and more susceptible to political and cultural cues. That is particularly dangerous for diseases such as measles.
The politics of trust
There is a temptation to describe the current moment as a battle between science and anti-science.That framing is emotionally satisfying, but incomplete. The deeper issue is trust.
A person who refuses a vaccine because of a false claim circulating on social media is responding to information. But a person who accepts that claim instead of information provided by a doctor, a public-health agency or a scientific institution is also making a judgment about whom to trust. The pandemic exposed how fragile that trust can become when political leaders, institutions and experts deliver conflicting messages.
It also demonstrated that polarization does not necessarily last forever. Research tracking Covid-19 vaccination in Brazil found that the initial gap in adherence between conservatives and non-conservatives narrowed over time, driven largely by faster uptake among people who had initially been more skeptical.
That finding matters because it suggests that political identity does not permanently determine vaccine behavior. People can change their minds, but rebuildinh confidence is slower than destroying it.
What measles is really exposing
Brazil has the infrastructure. It has one of the world’s largest public immunization programs. It has recovered much of the ground lost during the pandemic. And the latest international data show that Brazil is moving in the right direction. Even when high national averages can hide local vulnerabilities.
A few percentage points of lost coverage may look insignificant on a national spreadsheet. In a densely populated city connected to the rest of the world by airports, however, those missing vaccinations can become the space through which a highly contagious virus moves.
That is why the return of measles should not be read simply as evidence that Brazilians have become anti-vaccine. Nor should it be dismissed as an isolated consequence of international travel.
It is a warning about what happens when public-health achievements are taken for granted, when misinformation becomes politically profitable and when scientific questions become symbols of political loyalty. The most important question may therefore not be whether vaccination in Brazil is left-wing or right-wing. It is whether it can become politically uninteresting again.
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The article above was edited by Ana Rita Rodrigues Fernandes.
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