![]() The effectiveness of the influenza vaccine varies from year-to-year, often because there are differences between the strains targeted by the vaccine and the strains circulating and infecting people each year. While flu shots are needed annually to maintain optimal levels of protection, the main reason subsequent shots are given is because the influenza vaccine is updated each year to account for virus mutations. Is the annual flu shot an example of a multi-dose vaccination?Ī vaccine with a multi-dose series differs from the annual flu shot. There is no recommendation for a booster shot at this time but Moderna, one of the manufacturers of an authorized vaccine states that while its vaccine is expected to be protective against COVID-19 variants, the company is exploring whether a booster can offer additional protection and Pfizer, the other manufacturer, has indicated that boosters are likely needed. require a two-dose series to achieve highest levels of immunity. The COVID-19 vaccines that have been authorized in the U.S. For instance, the human papillomavirus (HPV) vaccine is given in either two or three dose series, depending on age of initial vaccination. The number of doses in a vaccination series can be the same for everyone or differ based on risk group, age, and other factors. In addition, following the primary vaccination or vaccination series, certain vaccines require a booster for all people or certain groups of people after a period of time to improve waning immunity. In some cases, multiple doses are necessary to achieve the highest possible levels of immunity, whereas in others, a second dose is administered because not all individuals respond sufficiently to a single dose. Why do some vaccinations require multi-dose series? Timing and Spacing of Immunobiologics, November 17, 2020. Table 2: Conditions with Vaccines Requiring Multi-dose Series In fact, nearly all vaccines recommended for children and adolescents and many adult vaccinations, require a series of more than one dose (Table 2). Sources: Pfizer-BioNTech Vaccine VRBPAC Briefing Document Moderna COVID-19 Vaccine VRBPAC Briefing Document Safety and Efficacy of the ChAdOx1 nCoV-19 Vaccine Against SARS-CoV2 “Should We Change COVID Vaccine Doses to Reach More People? What the Data Say.” Oliver, S., “ Work Group Interpretations of Data,” Presentation to ACIP. Immune protection may not begin until about two weeks following the first dose data are not available on long-term protection after only one dose. Notes: **Clinical trials for the vaccines were designed to study efficacy after two doses data on single dose efficacy are not as complete as that for two doses. Table 1: FDA Authorized COVID-19 Vaccines, Schedules, and EffectivenessĮstimated Efficacy Between Dose 1 and Dose 2** This issue brief examines key issues related to multi-dose vaccination series generally as well as issues specific to COVID-19. Additionally, as COVID-19 vaccines have rolled out, there have been discussions about the appropriateness of flexibility in dosing schedules to accelerate first doses for more people there is also a likelihood that a third vaccine from Johnson & Johnson, that uses only one dose, could be authorized soon. ![]() ![]() In the context of routine immunization, multi-dose vaccine series are relatively common, but have also presented challenges for ensuring vaccine series completion where in many cases, there is a drop-off in uptake between the first and subsequent doses. In fact, in the COVID-19 vaccine playbook provided to states by the Centers for Disease Control and Prevention (CDC), the issue of second dose reminders was identified as a key area to be addressed. intensify, one key challenge is ensuring people get both the first and second dose. As efforts to promote equitable and rapid distribution and uptake of the vaccine in the U.S. ![]() There are currently two COVID-19 vaccines authorized for use in the United States, both of which require a two-dose series (see Table 1).
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