Three, four or more: what’s the magic number for booster shots?

Safety, immunogenicity, and reactogenicity of BNT162b2 and mRNA-1273 COVID-19 vaccines given as fourth-dose boosters following two doses of ChAdOx1 nCoV-19 or BNT162b2 and a third dose of BNT162b2 (COV-BOOST): a multicentre, blinded, phase 2, randomised trial

“…Observational data from Israel have shown a boosting effect on immunogenicity 6 and moderate protection against symptomatic infection from a fourth dose of mRNA COVID-19 vaccines administered approximately 4 months after a third dose. 7 , 8 The clinical need, timing, and dose of the fourth COVID-19 vaccine remain uncertain, 9 as does the gain in vaccine effectiveness compared with a third dose. Given the urgent need for data to inform policy on additional booster doses, the COV-BOOST trial 1 of third-dose booster vaccines for COVID-19 was extended to investigate the safety, reactogenicity, and immunogenicity of fourth-dose boosters against COVID-19 administered approximately 7 months following a third dose of BNT162b2 (Pfizer-BioNTech).…”

The Omicron wave and the waning of COVID-19 vaccine effectiveness. Influence of vaccine booster and age on confirmed infection incidence

“…On the other hand, the protection against severe illness did not wane as fast as the protection against a confirmed infection, and a third doses could be enough to avoid severe cases of COVID-19. Beyond the fourth dose [10] , vaccination strategies are being optimized with heterologous vaccination schedules and optimal time interval between doses. The next logic step will be the development of variant-adapted vaccines.…”

The impact of COVID-19 vaccines on the Case Fatality Rate: The importance of monitoring breakthrough infections

“…This reinforces that widespread testing is still a key policy strategy to detect asymptomatic or mild infections among both the vaccinated and unvaccinated populations ( The Rockefeller University, 2021 ). Effort s to properly detect those cases are important for assessing immunity duration ( Seow et al, 2020 ) and if extra booster shots will be needed, especially with new, more contagious variants spreading quickly throughout the world and more breakthrough infections recorded ( Kupferschmidt, 2021 ;Barda et al, 2021 ;Arbel et al, 2021 ;Andrews et al, 2022 ;Watson, 2022 ). This may be a decisive factor in informing governments on the different set of strategies they may need to employ throughout the pandemic, including a mixture of vaccines and nonpharmaceutical measures , as immunity to SARS-CoV-2 infection may progressively wane with time ( Haghpanah et al, 2021 ;Reynolds, 2021 ;Stamatatos, 2021 ).…”