Odds of Testing Positive for SARS-CoV-2 Following Receipt of 3 vs 2 Doses of the BNT162b2 mRNA Vaccine

Abstract

IMPORTANCE With the evidence of waning immunity of the mRNA vaccine BNT162b2 (Pfizer-BioNTech), a nationwide third-dose (booster) vaccination campaign was initiated in Israel during August 2021; other countries have begun to administer a booster shot as well.OBJECTIVE To evaluate the initial short-term additional benefit of a 3-dose vs a 2-dose regimen against infection of SARS-CoV-2.DESIGN, SETTING, AND PARTICIPANTS This preliminary retrospective case-control study used 2 complementary approaches: a test-negative design and a matched case-control design. Participants were included from the national centralized database of Maccabi Healthcare Services, an Israeli healthcare maintenance organization covering 2.5 million members. Data were collected between March 1, 2020, and October 4, 2021, and analyses focused on the period from August 1, 2021, to October 4, 2021, because the booster dose was widely administered from August 1 onward.EXPOSURES Either 2 doses or 3 doses of the BNT162b2 vaccine. MAIN OUTCOMES AND MEASURESThe reduction in the odds of a positive SARS-CoV-2 polymerase chain reaction (PCR) test at different time intervals following receipt of the booster dose (0-6, 7-13, 14-20, 21-27, and 28-65 days) compared with receiving only 2 doses. RESULTSThe study population included 306 710 members of Maccabi Healthcare Services who were 40 years and older (55% female) and received either 2 or 3 doses of the BNT162b2 vaccine and did not have a positive PCR test result for SARS-CoV-2 prior to the start of the follow-up period. During this period, there were 500 232 PCR tests performed, 227 380 among those who received 2 doses and 272 852 among those who received 3 doses, with 14 989 (6.6%) and 4941 (1.8%) positive test results in each group, respectively. Comparing those who received a booster and those who received 2 doses, there was an estimated odds ratio of 0.14 (95% CI, 0.13-0.15) 28 to 65 days following receipt of the booster (86% reduction in the odds of testing positive for SARS-CoV-2). CONCLUSION AND RELEVANCEPrevious studies have demonstrated that vaccine-derived protection against SARS-CoV-2 wanes over time. In this case-control analysis, we showed an association between receipt of the booster dose and a reduction in the odds of testing positive for SARS-CoV-2, potentially counteracting waning immunity in the short term. Further monitoring of data from this population is needed to determine the duration of immunity following the booster.

Duration of Protection against Mild and Severe Disease by Covid-19 Vaccines

“…Israel was one of the first countries to immunize adults with the BNT162b2 vaccine and began offering a third dose of the same vaccine to older adults starting in July 2021. 23 Early data indicate that the third dose was associated with large reductions in the incidence of SARS-CoV-2 infection within 1 week after vaccination, with greater reductions in the second week. 23 The duration of protection offered by the third dose, however, is uncertain.…”

“… 23 Early data indicate that the third dose was associated with large reductions in the incidence of SARS-CoV-2 infection within 1 week after vaccination, with greater reductions in the second week. 23 The duration of protection offered by the third dose, however, is uncertain. Many countries, including the United Kingdom and the United States, are now offering a third dose.…”

The emergence of new SARS-CoV-2 variant (Omicron) and increasing calls for COVID-19 vaccine boosters-The debate continues

“…The scientific rationale for boosters includes concerning evidence regarding declining vaccination protection over time and increased worries about breakthrough infections caused mainly by the SARS-CoV-2 Delta strain. The evidence for boosters comes from a variety of sources, including real-world data from Israel [ [11] , [12] , [13] ], the United Kingdom [ 14 ], and the USA [ 15 ], which showed that a booster dose of one of the commonly used mRNA-based vaccinations significantly reduces a person's chances of contracting SARS-CoV-2 and becoming mildly sick. A recent Pfizer research [ 16 ], which included data from over 44 000 people, indicated that after 6 months, vaccination protection dropped from 96.2% to 83.7%.…”

The challenge of limited vaccine supplies: impact of prior infection on anti-spike IgG antibody trajectories after a single COVID-19 vaccination

“…Based on the positivity threshold and previously reported correlates of protection, those with prior infection could be protected from infection for >1 year after a single vaccination. While recent studies show that a third vaccination boosts antibody responses 29 and provides better protection against infection than two vaccinations 30 , and two vaccinations plus prior infection provides better protection against re-infection than prior infection alone 8 , a large part of the global population did not yet have the chance to get their first vaccination due to limited vaccine supplies. These results could inform vaccine strategies, providing an evidence-base to optimise population immunity in the context of resource limitations, while international SARS-CoV-2 immunisation programmes are scaled up and secured.…”