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Fourth jab slashes breakthrough COVID infections – Israeli cohort study

There are definite benefits to administering a fourth dose of the COVID vaccine, say researchers, after a cohort study of 29  611 healthcare workers in Israel saw a breakthrough infection rate, among those who received four doses, of just 6.9%, compared with 19.8% in those who received three doses.

In December 2021, the fifth COVID-19 wave started in Israel, caused mostly by the Omicron variant and affecting the unvaccinated and vaccinated populations.

Israel was the first country to administer a third vaccine dose to the entire adult population, beginning in August 2021. Ninety percent of adults in the country, including more than 95% of healthcare workers, received three doses of the BNT162b2 vaccine until September 2021. This third dose (booster) vaccine markedly reduced the rate of breakthrough infections, severe disease and mortality during the Delta variant wave.

Despite this high vaccination rate, the highly infectious Omicron variant caused a significant number of breakthrough infections among the thrice-vaccinated population.

After the success and safety of the third dose in preventing infection and severe disease, and assuming waning immunity of the third dose, the Israeli Ministry of Health recommended a voluntary fourth BNT162b2 dose to adults older than 60, those who were immunocompromised, and healthcare workers.

During the peak of Omicron activity, we compared breakthrough infection rates between the workers who had received three versus four doses of the BNT162b2 vaccine.

Eleven Israeli hospitals participated in the initial study: all are academic centres, five of which are tertiary care centres. Healthcare workers were vaccinated with Pfizer’s BNT162b2 messenger RNA vaccine. In total, the participating centres included approximately half of the total acute care beds in Israel and cover all areas of Israel.

Study details

Association of Receiving a Fourth Dose of the BNT162b Vaccine With SARS-CoV-2 Infection Among Health Care Workers in Israel

Matan J. Cohen, Yonatan Oster, Allon Moses, et al

Published in JAMA Network Open on 2 August 2022

Key Points

Question Was there a benefit of vaccinating health care workers with a fourth dose of BNT162b2 vaccine during the Omicron variant outbreak of the COVID-19 pandemic?
Findings In this multicentre cohort study of 29, 611 health care workers in Israel, the breakthrough infection rate among those who received four doses was 6.9% compared with 19.8% in those who received three doses.
Meaning These findings suggest that a fourth vaccine dose was effective in preventing breakthrough COVID-19 infections in healthcare workers, helping to maintain the function of the healthcare system during the pandemic.

Abstract

Importance
Despite the high three-dose vaccination rate among health care workers (HCWs) in Israel, a high rate of SARS-CoV-2 breakthrough infections in this group was observed during the Omicron wave. As a result, the Israeli Ministry of Health decided to recommend a fourth vaccine dose to medical staff.

Objective
To evaluate the benefit of a fourth BNT162b2 vaccine dose on the breakthrough infection rate among HCWs.

Design, Setting, and Participants
This multicentre cohort study was performed in January 2022, the first month of the four-dose vaccination campaign, during a surge of the Omicron variant wave. All health care workers at 11 general hospitals in Israel who had been vaccinated with three doses up to September 30, 2021, and had not contracted COVID-19 before the vaccination campaign were included.

Exposures
Vaccination with a fourth dose of the BNT162b2 vaccine during January 2022.

Main Outcomes and Measures
Breakthrough COVID-19 infections in 4-dose recipients vs 3-dose recipients measured by a polymerase chain reaction test result positive for SARS-CoV-2. Health care workers were tested based on symptoms or exposure.

Results
A total of 29,611 Israeli HCWs (19 381 [65%] female; mean [SD] age, 44 [12] years) had received 3 vaccine doses between August and September 2021; of these, 5,331 (18%) received the fourth dose in January 2022 and were not infected by the first week after vaccination. Overall breakthrough infection rates were 368 of 5,331 (7%) in the 4-dose group and 4802 of 24280 (20%) in the 3-dose group (relative risk, 0.35; 95% CI, 0.32-0.39). Similar reductions were found in a matched analysis by the exact day of receiving the third vaccine (relative risk, 0.61; 95% CI, 0.54-0.71) and in a time-dependent Cox proportional hazards regression model (adjusted hazard ratio, 0.56; 95% CI, 0.50-0.63). In both groups, no severe disease or death occurred.

Conclusions and relevance
In this cohort study, the fourth BNT162b2 vaccine dose resulted in a reduced breakthrough infection rate among hospital staff. This reduction was lower than that observed after the third dose; nevertheless, considering the high infectivity of the Omicron variant, which led to critical medical staff shortages, a fourth vaccine dose should be considered to mitigate the infection rate among HCWs.

 

JAMA Network Open article – Association of Receiving a Fourth Dose of the BNT162b Vaccine With SARS-CoV-2 Infection Among Health Care Workers in Israel

 

See more from MedicalBrief archives:

 

Fourth COVID jab gives 76% added protection against death – Israeli study

 

4th jab can give higher immunity than initial booster – Cov-Boost trial

 

Second Pfizer booster only protects short-term against Omicron – Large Israeli study

 

UK vaccination committee says 4th booster not necessary

 

 

 

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