These shots work, and they represent the most powerful tool available
En la primavera de 2021, cuando el mundo buscaba señales de esperanza en medio de una pandemia que había reconfigurado la vida cotidiana, los Centros para el Control y la Prevención de Enfermedades de Estados Unidos ofrecieron una respuesta concreta: las vacunas de Pfizer-BioNTech y Moderna reducían el riesgo de infección por COVID-19 en un 90 por ciento entre quienes habían completado el esquema de dos dosis. El hallazgo, observado en trabajadores de salud y personal esencial —aquellos que más habían cargado con el peso de la crisis— confirmaba que la ciencia desarrollada a velocidad sin precedentes podía sostenerse en el mundo real. En ese mismo momento, Rusia respondía con su propia cifra para la Sputnik V, convirtiendo los datos de eficacia en una nueva forma de competencia entre naciones.
- Con millones de personas esperando su turno para vacunarse, la presión por demostrar que las vacunas funcionaban fuera de los ensayos clínicos era inmensa y urgente.
- Los trabajadores de salud y primeros respondedores, los más expuestos al virus durante más de un año, se convirtieron en la prueba viviente de que la protección era real y alcanzable.
- La directora del CDC, Rochelle Walensky, lanzó un mensaje claro hacia una población agotada: las vacunas cumplen su promesa, y la protección comienza incluso antes de completar el esquema.
- Días después del anuncio estadounidense, los desarrolladores de la Sputnik V respondieron en Twitter con una eficacia del 91,6%, transformando los datos científicos en un campo de batalla de prestigio nacional.
- Detrás de los números competitivos, una verdad compartida comenzaba a imponerse: las vacunas disponibles en 2021 superaban las expectativas más optimistas del inicio de la pandemia.
A finales de marzo de 2021, cuando las campañas de vacunación ganaban impulso en Estados Unidos, el CDC publicó datos que daban a los funcionarios de salud pública algo concreto a lo que señalar: las vacunas de Pfizer-BioNTech y Moderna reducían el riesgo de infección por COVID-19 en un 90 por ciento entre quienes habían recibido las dos dosis necesarias. La información provenía de la observación directa de trabajadores de salud, socorristas y personal esencial —el grupo con mayor exposición al virus y, por tanto, el más revelador para medir si las vacunas funcionaban fuera de un entorno controlado.
Rochelle Walensky, directora del CDC, presentó los resultados como una validación del esfuerzo nacional de vacunación. Subrayó que la protección comenzaba a desarrollarse dos semanas después de la primera dosis, aunque el escudo más sólido llegaba únicamente al completar el esquema completo. Para los millones de estadounidenses ya vacunados o próximos a serlo, el mensaje era directo: estas vacunas funcionan y representan la herramienta más poderosa disponible para poner fin a la pandemia.
Los hallazgos del CDC aterrizaron en un paisaje ya saturado de afirmaciones competitivas. En cuestión de días, los desarrolladores de la vacuna rusa Sputnik V anunciaron en Twitter su propia cifra de eficacia: 91,6 por ciento. El dato fue presentado como una superioridad sobre las vacunas estadounidense y alemana. Alexander Gintsburg, director del Centro Nacional de Investigación Gamaleya, añadió que la vacuna mostraba efectividad consistente en todos los grupos de edad aprobados, era bien tolerada y se esperaba que la inmunidad durara más de dos años.
Lo que emergió de estos anuncios paralelos fue una instantánea del primer capítulo de la era vacunal: un momento en que los datos de eficacia se convirtieron en una forma de prestigio nacional, y distintos países competían no solo por proteger a sus poblaciones, sino por reclamar credibilidad en un mercado global. Más allá de los porcentajes en disputa, ambas cifras contaban la misma historia esencial: las vacunas desplegadas en 2021 eran mucho más eficaces de lo que muchos habían osado esperar cuando comenzó la pandemia.
In late March 2021, as vaccination campaigns were ramping up across the United States, the CDC released findings that gave public health officials something to point to: the Pfizer-BioNTech and Moderna vaccines were reducing the risk of COVID-19 infection by 90 percent among the people who had received both required doses. The data came from real-world observation of healthcare workers, first responders, and other essential personnel who had been among the first to roll up their sleeves—the group most likely to encounter the virus and most likely to show whether the vaccines actually worked outside the controlled environment of a clinical trial.
Rochelle Walensky, the director of the CDC, framed the results as validation of the national vaccination effort itself. The vaccines that had been authorized for emergency use were delivering on their promise in the actual world, she said, offering protection to the frontline workers who needed it most. She emphasized that protection began to develop two weeks after the first injection, though the strongest shield came only after people completed the full two-dose series. For millions of Americans who were either already vaccinated or waiting their turn in the coming weeks, Walensky's message was direct: these shots work, and they represent the most powerful tool available to bring the pandemic to an end.
The CDC findings landed in a landscape already crowded with competing claims about vaccine performance. Within days, developers of Russia's Sputnik V vaccine took to Twitter to announce their own efficacy figure: 91.6 percent. The claim was framed as a point of superiority over the American and German vaccines, suggesting that the Russian shot not only matched but exceeded the protection offered by Pfizer and Moderna. Alexander Gintsburg, the director of the Gamaleya National Research Center for Epidemiology and Microbiology, which had developed Sputnik V, added further details: the vaccine showed consistent effectiveness across all age groups approved for its use, recipients tolerated it well, and the developers expected immunity to last more than two years.
What emerged from these competing announcements was a snapshot of the early vaccine era—a moment when efficacy data became a form of national prestige, when different countries and manufacturers were racing not just to protect their populations but to claim superiority in the global competition for credibility and market share. The CDC's 90 percent figure was grounded in observation of American healthcare workers and essential personnel. The Sputnik V claim of 91.6 percent came with less transparency about the underlying data and methodology. Both numbers, however, told the same essential story: the vaccines being deployed in early 2021 were far more effective than many had dared hope when the pandemic began.
For the people receiving these vaccines in the spring of 2021, the specific percentages mattered less than the basic fact: protection was real, it began within weeks, and it strengthened after the second dose. The CDC director's emphasis on hope—directed at the millions already vaccinated and those about to be—reflected a genuine turning point. The vaccines were working. The question now was whether the world could vaccinate fast enough to outpace the virus's spread.
Citas Notables
These authorized vaccines provided early and substantial real-world protection against infection for healthcare workers, first responders, and other essential frontline workers— Rochelle Walensky, CDC Director
The authorized vaccines are the key tool that will help end this devastating pandemic— Rochelle Walensky, CDC Director
La Conversación del Hearth Otra perspectiva de la historia
Why did the CDC release this data specifically about healthcare workers and essential personnel rather than the general population?
Because those groups had the earliest and most complete vaccination records. They were vaccinated first, they had the most exposure to the virus, and their outcomes would show whether the vaccines actually prevented infection in the real world, not just in a trial.
The Sputnik V response came almost immediately. Was that a coincidence?
No. By March 2021, vaccines had become a matter of national competition. Russia wanted to demonstrate that their vaccine was not just effective but superior. Posting a higher efficacy number on Twitter was a way to claim victory in a race that was as much about geopolitics as it was about public health.
Did the higher number for Sputnik V change how people viewed the Pfizer and Moderna vaccines?
Not significantly in the United States, where the CDC data was what people trusted. But in other countries, especially those considering which vaccine to use, the competing claims created confusion. People didn't know which number to believe or what the differences really meant.
What was the practical difference between 90 percent and 91.6 percent efficacy?
Mathematically, not much. But symbolically, everything. One number said the American vaccines were highly effective. The other said the Russian vaccine was slightly better. In the context of a pandemic, that small difference became a talking point in a much larger argument about which country had the better science.
Did the promise of immunity lasting two years matter to people at the time?
It mattered to governments planning their vaccination strategies. If immunity lasted two years, they would need to plan for boosters. But in March 2021, most people were just focused on getting their first dose. The question of what happened after two years felt abstract.