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The relative effectiveness of the fourth dose of a COVID-19 vaccine in the elderly was negligible within months, according to a new study.
Researchers in Italy measured the Relative Vaccine Effectiveness (RVE) against infection and severe disease. In other words, they compared the effectiveness of the fourth vaccine dose with the third dose. The population studied was people 80 years old and older.
Researchers found that the relative effectiveness against infection became negligible after two to four months. The relative effectiveness against severe illness was about 30 percent in the same time interval.
The study was conducted from April 11 to Aug. 6, when Omicron BA.2 and BA.5 subvariants were dominant, and published in Vaccine on Nov. 17.
The cost-benefit of a fifth vaccine dose for the elderly people who received the fourth dose at least four months earlier “should be carefully evaluated,” the authors concluded.
Researchers in the study linked data from the national vaccination registry to the COVID-19 surveillance system. They matched individuals who received the fourth vaccine dose with individuals who received the third vaccine dose at least 120 days earlier.
The analysis was based on 831,555 matched pairs in total.
The type of messenger RNA (mRNA) vaccines included in the study were both BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna).
The RVE “against infection was found to decrease over the four-months follow-up period, showing no additional protection 56–118 days post administration,” the authors said.
The RVE of the fourth dose decreased from 28.5 percent in the time interval of 14–28 days to 7.6 percent in the time interval of 56–118 days.
RVE against severe COVID-19 was higher and it decreased from 43.2 percent to 27.2 percent over the same time intervals.
The authors said that the limitations of the paper included a short observation period that limited investigation of the waning of vaccine-induced protection.
The authors declared that they had no competing interests.
UK Study on Vaccine Effectiveness
Another study that was recently published also found vaccine effectiveness dropped to negligible levels within months.
British researchers found that the incremental vaccine effectiveness waned significantly after 25 weeks. The incremental VE was 16.2 percent, 23.8 percent, and 9.0 percent for BA.4, BA.5, and BA.2 subvariants at 25 or more weeks.
The study analyzed data from April 18 to Aug. 28 in elderly people 75 and older. It was published in The Lancet on Nov. 10.
Researchers also found that VE against hospitalization decreased significantly over time.
Incremental VE against hospitalization with subvariants BA.4/5 at 2–14 weeks after receiving a third or fourth dose was 63.2 percent and 53.1 percent for mRNA-1273 and BNT162b2, respectively. This decreased to 40.2 percent and 23.7 percent for mRNA-1273 and BNT162b2, respectively, at 15–24 weeks.
Pfizer and Moderna did not respond to requests for comment.
Reassessment of Future Booster Campaigns
An Israeli study published in early November found that short-lived immunity and rapid waning of the Pfizer BioNTech COVID-19 vaccine necessitate the reevaluation of future COVID-19 vaccination campaigns.
The authors of that study said that “its relatively small effect on transmissibility of Omicron … and its rapid waning call for reassessment of future booster campaigns.”
The results indicated that if the lack of sterilizing immunity proves consistent, it “may have major ramifications on global pandemic preparedness” and vaccination rollout.
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