SARS-CoV2 breakthrough infections in elderly third booster and vaccinated population considered vaccine immune during omicron (B.1.1.529) variant surge in Israel.

The fourth booster vaccination was approved in Israel during Omicron (B.1.1.529) variant surge due to increasing SARS-CoV2 breakthrough infections among recently vaccinated, reasons for this resurgence is not clear. In this Observational study, we analyzed verified SARS-CoV2 infections among over 60 years of age based on vaccination schedule (December 20, 2020-January 29, 2022); infections, severe illness and deaths based on vaccine immunity (between August 1, 2021-January 29, 2022) using Israel COVID-19 dashboard data. There were a total of 214,394 SARS-CoV2 infections (December 20, 2020-Janaury 29, 2022; based vaccination schedule), 165,899 infections; 6,267 severe illnesses and 2,031 deaths (August 1, 2021-Janaury 29, 2022) analyzed based vaccine immunity among over 60 years old. Vaccination with two doses, maintained vaccine effectiveness (VE) of 93.2% (95% CI 90-95.5%) for 16 weeks until May 8, 2021 with 14.2% breakthrough infections. When there were no public health restrictions (June-July 2021) partially vaccinated has significantly lower infection rates (X² [2, N=721]=190.79, p<0.001) with VE of 80.4% (95% CI 69.1-98.3%), while infection rates among vaccinated with two doses and unvaccinated are not statistically significant and decline of VE to 6.4% (95% CI -9.9-19.3%) among vaccinated with two doses. After reinstatement of restrictions since July 29, 2021, the VE of vaccinated with two doses improved to 68.0% (95% CI 56.7-76.7%), the third booster showed significantly higher breakthrough infections (26.4%) and a shorter period of 12 weeks effectiveness until October 23, 2021 and by November 20, 2021 the infections rates of vaccinated with third booster are not statistically better than partially vaccinated (X² [1, N=54]=1,85, p=0.17). During the Omicron variant surge, the VE of third booster declined to 42.7% (95% CI 39.9-45.3%) and the infection rates were significantly higher than vaccinated with two doses (X²[1,N=5898]=8.50, p=0.003) as of January 15, 2022 and subsequently showed improvement in VE to 51.7% (95% CI 50.2-53.2%) and significantly lower infection rates than vaccinated with two doses (X²[1,N=12380]=98.28, p=<0.001) by January 29, 2022. The vaccinated without validity group (partially vaccinated; past 1-2 doses with expired Green Passes) showed significantly lower infection rates (X² [1, N=15727]=295.3, p<0.001) during December 5,2021-January 29, 2022 period compared to vaccinated with validity (95% of them received third booster dose, and have Green Pass access) group that showed significantly increased infection rates and substantially increased percentages of severe illness and deaths. Vaccination with the third booster associated with brief protection and higher breakthrough infections compared to prior vaccination with two doses. The vaccinated population, who are considered immune according to the new vaccination policy, showed significantly increased infections, substantial increases in severe illness, and deaths during Omicron surge. However, those considered non-immune showed significantly decreased infections. There was a stronger association between public health restrictions and infections among the vaccinated groups. There is an urgent need to protect the elderly population by adopting uniform protective measures and surveillance protocols.