Antibody levels from vaccination wane over time, generally over the course of several months post-vaccination before leveling off. Following vaccination, a person’s antibodies will rise over time and generally peak around 3-4 weeks post-vaccination. Antibodies are proteins made by a person’s immune system in response to infections or vaccination that can protect against future infections. Blood samples are collected from people prior to vaccination and then again about 3-4 weeks post-vaccination to allow time for their bodies to develop antibodies. The blood samples are collected during the flu season, and this work begins shortly after flu vaccines becomes available. To obtain this serology data, CDC works with partner organizations to collect blood samples from people who received flu vaccines. Human serology data are now included in the overall body of data that CDC collects to inform WHO’s Northern and Southern Hemisphere flu vaccine composition recommendations. Human serology data contribute to the selection of CVVs for flu vaccines.
Research indicates if the flu virus representing each vaccine component needs to be updated with a new CVV. Therefore, three or four candidate vaccine viruses (CVVs) are chosen for use in flu vaccine production.
Trivalent (three-component) flu vaccines contain only one flu type B virus. Quadrivalent flu vaccines contain a flu A(H1N1)pdm09 component, a flu A(H3N2) component, a flu B/Yamagata lineage component, and a flu B/Victoria lineage component. All available flu vaccines in the United States are quadrivalent (four-component) flu vaccines this season. Seasonal flu vaccines are designed to include CVVs that protect against the three or four (depending on vaccine) major flu virus groups ( known as types, subtypes, and lineages) that often co-circulate during flu seasons. For more information, visit Selecting Viruses for the Seasonal Flu Vaccine. VCM occurs in February to recommend the composition of Northern Hemisphere flu vaccines and in September to recommend the composition of Southern Hemisphere flu vaccines. These WHO consultations are called vaccine composition meetings (VCM). Twice a year, the World Health Organization (WHO) organizes a consultation with the seven WHO Collaborating Centers, Essential Regulatory Laboratories, and representatives from key national laboratories and academia to review available data and make recommendations on the composition of flu vaccines for the coming season. The selection of CVVs for producing seasonal flu vaccines is made months prior to the start of the flu season in the Southern and Northern Hemispheres. This is one reason why the composition of flu vaccines must be reviewed and updated and new vaccines produced prior to each flu season. More information is available at How the Flu Virus Can Change. All flu viruses undergo small genetic changes over time, and these genetic changes can result in antigenic changes that allow a flu virus to evade a person’s existing immunity from prior flu infection or vaccination. Flu viruses are always changing and many different flu viruses of various types and subtypes circulate around the world and cause seasonal flu epidemics. Human serology work to improve assessment and selection of CVVs for producing seasonal flu vaccinesĬDC’s Influenza Division now uses human serology data to improve the selection of candidate vaccine viruses (CVVs) for use in producing seasonal flu vaccines.
CDC Influenza Division’s human serology work supports the following objectives: Serology is the scientific study of blood to look at the response of the immune system to vaccination or infections with pathogens, like flu viruses.
To improve seasonal flu vaccines and prepare against future pandemics, CDC’s Influenza Division conducts a wide range of laboratory activities involving human serology. CDC Human Serology Efforts to Improve Seasonal Flu Vaccines and Prepare Against Future Flu Pandemics
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