FOCUS BOOSTER OLD VERSION SERIES

National vaccination programme policy decisions to add a booster dose should take into account the strength of evidence regarding the need for these doses and global availability of vaccines. Global vaccine supply and global and national equity While breakthrough infections are still expected, the vast majority are less severe than those seen in unvaccinated people (5).ģ. However, some reduction in vaccine effectiveness has been reported for some VOCs. Data from Israel suggest that around 40% of breakthrough infections are in immunocompromised individuals (4).

Although there may be a loss of protection against infections by SARS-CoV-2 protection against severe disease is likely to be largely retained due to cell mediated immunity (1).ĭata are currently insufficient to determine if there is a significant decline in vaccine effectiveness against any form of clinical illness from SARS-CoV-2 infection beyond 6 months after vaccination. While data on immunogenicity of some vaccines suggest that antibodies persist for at least 6 months (2), waning of neutralizing antibodies has been reported (3). Neither an immune correlate of protection nor an immune correlate for the duration of protection has been established to date. Studies suggest a correlation between the efficacy of different vaccines against symptomatic disease and mean neutralizing antibody titers induced by those vaccines (1), but it is unclear if declining titers over time since vaccination are indicative of declining vaccine effectiveness, especially against VOCs. The rationale for booster doses may differ by vaccine product, epidemiological setting, risk group, and vaccine coverage rates.

FOCUS BOOSTER OLD VERSION SERIES

There are several reasons why COVID-19 vaccine booster doses may be needed: (i) waning protection against infection or disease, in particular severe disease, over time (i.e., waning immunity), (ii) reduced protection against variant(s) of concern (VOC), or (iii) inadequate protection from the currently recommended primary series for some risk groups for which evidence from the Phase 3 clinical trials may have been lacking.

WHO, with support of the Strategic Advisory Group of Experts (SAGE) on Immunization and its COVID-19 Vaccines Working Group, is reviewing the emerging evidence on the need for and timing of an additional vaccine dose (booster dose 1) for the currently available COVID-19 vaccines which have received Emergency Use Listing (EUL). SAGE is continuously reviewing the literature and has reached out to vaccine manufacturers, the research community and Member States to obtain the most complete and recent data on the issue.

Focus booster old version