Safety and efficacy are different things entirely
Em setembro de 2020, São Paulo anunciou dados de segurança promissores para a Coronavac, uma vacina desenvolvida em parceria entre a chinesa Sinovac e o Instituto Butantã, com base em um estudo envolvendo cinquenta mil voluntários na China. Quase 95% deles não relataram efeitos adversos, um perfil comparável ao das vacinas contra a gripe já consolidadas no país. Ainda assim, a ciência e a política caminhavam em ritmos distintos: enquanto os ensaios de eficácia da fase 3 ainda estavam em andamento, o governador João Doria já projetava vacinações em massa para dezembro, transformando uma promessa científica em símbolo de gestão e ambição.
- Com o mundo em busca urgente de uma saída para a pandemia, São Paulo apresentou dados de segurança da Coronavac como se fossem a antessala da vitória — mas os ensaios decisivos de eficácia ainda não tinham terminado.
- O governador Doria afirmou que a vacina mostrava 98% de efetividade, confundindo publicamente a produção de anticorpos com proteção real contra a infecção, o que especialistas em doenças infecciosas foram rápidos em corrigir.
- A corrida logística era ambiciosa: cinco milhões de doses previstas para outubro, sessenta milhões até fevereiro, e o início da vacinação marcado para dezembro — tudo condicionado à aprovação da Anvisa e ao desfecho dos testes clínicos.
- No cenário global, Brasil, Rússia e o consórcio AstraZeneca-Oxford disputavam espaço em um mercado de vacinas fragmentado, enquanto a OMS alertava que a imunização em massa provavelmente não ocorreria antes de 2022.
- Por trás dos anúncios científicos, analistas políticos enxergavam uma disputa de narrativas: para Doria, vacinar antes do governo federal seria uma declaração de competência — e um trampolim para uma possível candidatura presidencial.
Em setembro de 2020, o governador de São Paulo João Doria anunciou que um estudo com cinquenta mil voluntários na China havia confirmado o perfil de segurança da Coronavac, vacina desenvolvida em parceria entre a Sinovac e o Instituto Butantã. Quase 95% dos participantes não relataram qualquer efeito adverso, e os poucos que sentiram algo descreveram dor leve no local da aplicação, fadiga ou febre passageira — resultados comparáveis aos da vacina contra a gripe já amplamente usada no Brasil.
O anúncio, porém, carregava uma distinção importante que os holofotes tendiam a apagar. Aqueles cinquenta mil voluntários haviam recebido a vacina sob autorização emergencial, não como parte de um ensaio clínico formal. O estudo de fase 3, que determinaria se a vacina de fato prevenia a COVID-19, ainda estava em curso em vários países, incluindo o Brasil. Dimas Covas, presidente do Butantã, foi cuidadoso: resultados de eficácia só estariam disponíveis, no melhor cenário, em meados de outubro.
A confusão em torno da eficácia veio do próprio governador, que citou 98% de efetividade. O número se referia à soroconversão — a proporção de pessoas que produziram anticorpos após a vacinação. Mas anticorpos não são sinônimo de proteção. Alexandre Naime, chefe de infectologia da Unesp, foi direto: os dados disponíveis demonstravam apenas segurança. Se a vacina protegia contra a infecção, só o acompanhamento dos vacinados ao longo do tempo poderia responder.
No plano logístico, Doria já projetava um calendário ambicioso: cinco milhões de doses em outubro, sessenta milhões até fevereiro, e o início da vacinação em dezembro, sujeito à aprovação da Anvisa. O contexto era de competição aberta — o governo federal apostava na AstraZeneca, o Paraná e a Bahia negociavam a Sputnik V russa, e a OMS não previa imunização em massa antes de 2022. Para analistas políticos, a corrida pela vacina era também uma corrida por narrativa: vacinar antes e melhor seria, para Doria, uma declaração de competência em ano de olho nas eleições presidenciais.
On a September afternoon in 2020, São Paulo's governor João Doria stood before cameras with news that felt, in those early pandemic months, like a glimpse of the finish line. A study of fifty thousand people in China had shown that Coronavac—a vaccine being developed jointly by the Chinese pharmaceutical company Sinovac and Brazil's Butantã Institute—appeared to be safe. Nearly 95 percent of those who received it experienced no adverse effects at all, a safety profile comparable to the flu vaccine Brazilians had been taking for decades.
But the announcement contained a careful distinction that most headlines would gloss over. The fifty thousand people studied in China had received the vaccine under emergency authorization, not as part of a formal clinical trial. They were high-risk patients and Sinovac employees. The real test—the phase 3 efficacy trial that would actually prove whether the vaccine prevented COVID-19—was still running. It was happening in multiple countries, including Brazil, and the results were not yet in.
Doria, however, was already planning ahead. São Paulo expected to receive five million doses in October, with sixty million more by the end of February. The governor spoke of beginning vaccinations in mid-December, pending approval from Brazil's health regulator, the Anvisa. The Butantã Institute would produce forty million doses by late December, with another fifty-five million expected by May 2021. It was an ambitious timeline, built on hope and political will.
The safety data itself was reassuring in its specifics. Of the roughly fifty thousand people who received the vaccine in China, only 5.3 percent reported any side effects at all. The most common were soreness at the injection site, affecting just over three percent, followed by fatigue at 1.53 percent and fever at 0.21 percent. Only four volunteers experienced what could be called serious reactions—seven total adverse events among them, including loss of appetite, headache, and fever above 38.5 degrees Celsius. Dimas Covas, president of the Butantã Institute, was careful in his language. The phase 3 trial was ongoing, he said. Real efficacy data would not be available until mid-October at the earliest.
There was also the matter of what Doria had claimed about efficacy. The governor stated that the vaccine showed effectiveness in 98 percent of cases. What he meant, technically, was seroconversion—the percentage of people whose bodies produced antibodies in response to the vaccine. Antibodies are not the same as protection. A person can produce antibodies and still become infected. The distinction mattered, and it was one that infectious disease specialists felt compelled to clarify. Alexandre Naime, head of infectious diseases at Unesp, put it plainly: the only thing the clinical data actually showed was that the vaccine appeared safe. Whether it protected people from COVID-19 would only become clear over time, by watching whether vaccinated people got sick or not.
The broader context was one of global competition and domestic political stakes. Brazil's federal government had signed its own vaccine agreement with AstraZeneca and Oxford University. Paraná and Bahia had partnered with Russia for the Sputnik 5 vaccine. The World Health Organization had identified eight promising vaccine candidates worldwide. Having multiple vaccines in development was not a luxury; experts suggested it might be necessary to protect the population widely enough. Yet the timeline was tight. The WHO itself was not predicting mass immunization before 2022.
For Doria, the political dimension was impossible to separate from the medical one. If vaccinations began in December as he hoped, it would be a stark contrast to the federal government's handling of the pandemic. Political analysts noted that such a success would give him powerful ammunition for a potential presidential run. The vaccine had become not just a public health tool but a symbol of competence, of taking the crisis seriously, of being willing to act while others hesitated. The question was whether the science would move fast enough to match the politics.
Notable Quotes
The only thing the clinical data actually showed was that the vaccine appeared safe. Whether it protected people from COVID-19 would only become clear over time.— Alexandre Naime, head of infectious diseases at Unesp
The phase 3 trial is ongoing and the results are known only to those controlling the study. We don't yet have efficacy data available.— Dimas Covas, president of the Butantã Institute
The Hearth Conversation Another angle on the story
When Doria announced those numbers—94.7 percent with no side effects—why did that matter so much in September 2020?
Because people were terrified. The pandemic had killed hundreds of thousands. A vaccine that looked safe, even if efficacy wasn't proven yet, felt like proof that a way out existed. It gave people permission to hope.
But the efficacy data wasn't actually there. The 98 percent figure he mentioned—that was just antibodies, not protection.
Exactly. And the scientists knew it. But Doria needed to move. He had a political window. If he waited for perfect data, the moment would pass.
So he was gambling that the phase 3 trial would show what the safety data suggested—that this would work.
Not just gambling. He was betting that the urgency of the moment justified moving forward on incomplete information. Sixty million doses by February. That's not a cautious number.
What did the infectious disease experts actually think?
They were honest about the limits. They said: yes, it's safe. But safety and efficacy are different things. You can't know if it works until you watch people over time. Some said we might need to revaccinate, that immunity might not last. The unknowns were real.
And the political angle—was that cynical, or was Doria genuinely trying to solve a crisis?
Probably both. He was trying to solve it. But he also knew that being the governor who brought vaccines would reshape how people saw him. In a pandemic, those two things aren't separate.