A fourth dose, or second booster, of Pfizer/BioNTech (Comirnaty) COVID-19 vaccine protected seniors living in long-term care from the most severe outcomes during the Omicron wave, despite showing a more limited effect against infection, according to prospective data from Israel .
Among over 40,000 residents, the efficacy of a fourth dose (compared to a third given at least 4 months previously) was 64% and 67% in hospitalizations for mild/moderate and severe illness, respectively, and 72% in COVID-related deaths -19 , reported Khitam Muhsen, PhD, of Tel Aviv University in Israel.
The study was conducted from January to March 2022, when Omicron was the predominant strain and protection from infection by the highly contagious variant was only 34%.
Despite initial hesitation, Israel decided in December 2021 to give a fourth dose of Pfizer (BNT162b2) to groups at higher risk of severe COVID-19 – people aged 60 and over who had been vaccinated at least 4 months previously with their third dose. The decision was made “with the assumption that the fourth dose would likely increase levels of neutralizing antibodies that could provide cross-protection against the Omicron variant,” the group wrote JAMA Internal Medicine.
“The results of this study support the notion of cross-protection against the Omicron variant using the original formulation of the BNT162b2 vaccine,” they added. “Additionally, this booster could improve protection, likely due to increasing cross-reacting neutralizing antibody levels and enhancing cross-reactive cellular immunity against SARS-CoV-2 variants.”
The data from Muhsen and colleagues’ study came from 43,775 residents of long-term facilities in Israel, of whom 55% had received a fourth dose of Pfizer’s vaccine and 45% had only received a third dose at least 4 months previously. Patients in the study averaged 80 years of age and just over two-thirds were women. About 60% lived in geriatric facilities. The median follow-up time was 73 days.
At least one week after vaccination in the four-dose group, SARS-CoV-2 infections were reported in 4,058 people in the four-dose group (17.6%) and 4,370 people (24.9%) in the Group of three doses noted.
Major outcomes between the four-dose and three-dose recipients were as follows:
- Hospital admissions for mild/moderate illness: 0.9% vs. 2.8%
- Hospital admissions for serious illness: 0.5% vs. 1.5%
- Fatalities: 0.2% vs. 0.5%
An analysis looking at the same results at least 2 weeks after the fourth dose – when protection may have been increased – showed broadly comparable results, and a sensitivity analysis limited to residents who received the most tests (n=26,698) also yielded similar results with “slightly stronger point estimates,” the researchers noted.
Limitations included a lack of information about co-morbidities and individuals’ reasons for not receiving a fourth dose of the vaccine.
Despite this, “the results of this cohort study suggest a strong association between receiving a fourth dose of BNT162b2 and protection against COVID-19-related hospitalizations, serious illness, and death during the omicron surge,” the group concluded.
Muhsen reported no conflicts. A co-author announced relationships with AstraZeneca/MedImmune, GlaxoSmithKline, Pfizer, MSD and Sanofi Pasteur.