Lo que necesita saber
Las vacunas contra la influenza estacional están diseñadas para proteger contra la infección y la enfermedad causadas por los virus de la influenza que, según las investigaciones, serán los más comunes durante la próxima temporada de influenza. Flu vaccine effectiveness may vary based on how similar or different the vaccine virus is to circulating influenza viruses; however, even when the viruses are very different, vaccination can still prevent illness, hospitalization, and death. Flu vaccines protect against influenza viruses but do not protect against infection and illness caused by other viruses that also can cause flu-like symptoms.
Información general
There are many other viruses besides influenza viruses that can result in flu-like illness* (also known as influenza-like illness or "ILI") that spread during the flu season. These non-influenza viruses include, but are not limited to, the following:
- el SARS-CoV-2 (el virus que causa el COVID-19),
- el rinovirus (una de las causas del "resfriado común"), y
- el virus respiratorio sincitial (VRS), que es la causa más común de las enfermedades respiratorias graves en niños pequeños, así como una de las causas principales de enfermedades respiratorias graves en adultos de 65 años de edad o más.
Types and subtypes
The amount of protection provided by a flu vaccine may vary by influenza virus type or subtype and by vaccine, even when the viruses used to make flu vaccines are similar to the influenza viruses that are causing illness that season. Since 2009, VE studies looking at how well flu vaccines protect against medically attended illnesses have suggested better protection against influenza B and influenza A(H1N1) viruses than against influenza A(H3N2) viruses.
A metanalysis of 76 published VE studies conducted in countries in both the Northern and Southern Hemispheres after the 2009-2010 flu pandemic found flu vaccines performed the best against influenza A(H1N1)pdm09 viruses followed by influenza B viruses and were least effective against influenza A(H3N2) viruses.
En todos los estudios incluidos en el metanálisis, la estimación conjunta de VE contra todos los virus de la influenza para el hemisferio norte fue del 37 por ciento. En el caso de los virus de la influenza A(H1N1)pdm09, la estimación conjunta de VE para el hemisferio norte fue del 56 por ciento. En el caso de los virus de la influenza A(H3N2), la estimación conjunta de VE para el hemisferio norte fue del 22 por ciento.
Por último, para los virus de la influenza B, la estimación conjunta de VE correspondiente a los estudios del hemisferio norte fue del 42 por ciento. Overall, VE estimates were lower when the viruses used to make flu vaccines were less similar to the influenza viruses causing illness that season and decreased with older age.
A(H3N2) viruses
There are several reasons why flu vaccine effectiveness against influenza A(H3N2) viruses may be lower compared to other influenza viruses.
- While all influenza viruses undergo frequent genetic changes over time, the changes that have occurred in influenza A(H3N2) viruses have more frequently resulted in differences between the virus components of the flu vaccine and circulating influenza viruses (i.e., antigenic changes) compared with influenza A(H1N1) and influenza B viruses. That means that between the time when influenza viruses are selected to begin producing vaccines and when flu vaccines are delivered, A(H3N2) viruses are more likely than A(H1N1) or influenza B viruses to have changed in ways that could impact how well the flu vaccines work.
- Most inactivated seasonal flu vaccines produced by growing viruses in eggs. Mientras que todos los virus de la influenza sufren cambios cuando se cultivan en huevos, los cambios en los virus de influenza A(H3N2) tienden a ser más propensos a tener cambios antigénicos en comparación con los cambios que pueden tener otros virus de la influenza. Estos denominados "cambios adaptados en huevos" están presentes en el virus de la vacuna que se recomienda para el uso en la producción de vacunas y puede reducir su efectividad potencial contra los virus que circulan. Other types of flu vaccines, such as las vacunas a base de células y las vacunas recombinantes contra la influenza, are produce without the use of eggs, so the viruses used to make the vaccines do not undergo these changes. CDC is also using moleculares avanzadas detection (AMD) techniques to improve flu vaccines by providing experts with more data to support the selection of candidate vaccine viruses.