Changes in infectivity, severity and vaccine effectiveness against delta COVID-19 variant ten months into the vaccination program: The Israeli case

Abstract

We present epidemiological data to examine trends in COVID-19 incidence, morbidity and mortality in Israel as well as changes in vaccine effectiveness, and discuss the impact of the delta variant and the third, "booster", vaccine. A retrospective-archive study was conducted from February 27th 2020 to October 16th, 2021. Data were obtained from the Israeli Ministry of Health's open COVID 19 database, including PCR-confirmed cases, number hospitalized - including severe cases, death rate, all by age and vaccination status, case fatality rate and changing effectiveness of the vaccine. After three COVID waves, confirmed cases rose from under 30 new daily cases in mid-June to a high of 11,000 in early September 2021. Severe hospitalized cases and death rates were lower than in previous waves and largely restricted to those not fully vaccinated. In the first three months of the vaccination campaign, non-vaccinated population demonstrated much higher morbidity rates. Four months after vaccination began, this gap was attenuated, with low rates of infection and hospitalization in all groups. The gap was regained following uptake of the third vaccine. Data from the fourth wave show reduced hospitalizations and mortality compared to previous waves and suggest that this may be related to high vaccine coverage. These trends suggest that countries with high vaccination might adopt a more permissive approach towards COVID even in the face of new variants.

Keywords: COVID-19; Delta; Infectious diseases; Israel; Vaccination; Vaccine effectiveness; Variant.

Fig. 1

Daily COVID-19 activity, February 12, 2020 to October 16, 2021. 1a: Daily numbers of confirmed COVID-19 cases and 7-day moving average. 1b: Daily percent of positive tests.

Fig. 1

Daily COVID-19 activity, February 12, 2020 to October 16, 2021. 1a: Daily numbers of confirmed COVID-19 cases and 7-day moving average. 1b: Daily percent of positive tests.

Fig. 2

Severe hospitalized cases per 100,000 population, October 23, 2020 to October 21, 2021.

Fig. 3

COVID-19 activity and outcomes by vaccination status, 20/12/2020–16/10/2021. 3A. Rate of confirmed cases per 100,000 population. 3B: Rate of hospitalizations per 100,000 population. 3C: Rate of deaths per 1,00,000 populations.

Fig. 3

COVID-19 activity and outcomes by vaccination status, 20/12/2020–16/10/2021. 3A. Rate of confirmed cases per 100,000 population. 3B: Rate of hospitalizations per 100,000 population. 3C: Rate of deaths per 1,00,000 populations.

Fig. 3

COVID-19 activity and outcomes by vaccination status, 20/12/2020–16/10/2021. 3A. Rate of confirmed cases per 100,000 population. 3B: Rate of hospitalizations per 100,000 population. 3C: Rate of deaths per 1,00,000 populations.

Fig. 4

Confirmed cases, hospitalizations and deaths by vaccination status and age group, 20/12/2020–16/10/2021. 4a. Cumulative number of confirmed cases. 4b. Rate of hospitalizations per 100,000 confirmed cases. 4c. Number of cumulative deaths. 4d. Case fatality rate.

Fig. 4

Confirmed cases, hospitalizations and deaths by vaccination status and age group, 20/12/2020–16/10/2021. 4a. Cumulative number of confirmed cases. 4b. Rate of hospitalizations per 100,000 confirmed cases. 4c. Number of cumulative deaths. 4d. Case fatality rate.

Fig. 4

Confirmed cases, hospitalizations and deaths by vaccination status and age group, 20/12/2020–16/10/2021. 4a. Cumulative number of confirmed cases. 4b. Rate of hospitalizations per 100,000 confirmed cases. 4c. Number of cumulative deaths. 4d. Case fatality rate.

Fig. 4

Confirmed cases, hospitalizations and deaths by vaccination status and age group, 20/12/2020–16/10/2021. 4a. Cumulative number of confirmed cases. 4b. Rate of hospitalizations per 100,000 confirmed cases. 4c. Number of cumulative deaths. 4d. Case fatality rate.