"Conclusions
These findings indicate that immunity against the delta variant of SARS-CoV-2 waned in all age groups a few months after receipt of the second dose of vaccine.
Introduction
A key to the containment of the coronavirus disease 2019 (Covid-19) pandemic is mass vaccination of the population.
However, the success of this policy is challenged by breakthrough infection and disease in fully vaccinated persons.
One potential cause of breakthrough infection is the emergence of new variants of concern(1) that escape immunity, thus reducing the effectiveness of the vaccine.
Several studies investigating the effectiveness of the BNT162b2 vaccine (Pfizer–BioNTech) against the beta (B.1.351)(2),(3) and delta (B.1.617.2)(4), (5), (6) variants showed only modest rates of breakthrough infection and disease, whereas other studies showed higher rates.(7),(8)
A second potential cause of breakthrough infection is waning of the immunity conferred by the vaccine.
Mass vaccination with the BNT162b2 vaccine began in December 2020, and little is known about waning immunity over time.
A recent study on longer-term follow-up of the participants in the phase 2–3 randomized trial of the BNT162b2 vaccine9 showed a reduction in vaccine efficacy from 96% (in the period of 7 days to <2 months after receipt of the second dose) to 84% (in the period of 4 months to approximately 7 months after receipt of the second dose), which indicated a decrease in protection by a factor of four (i.e., [100−84]÷[100−96]).
Preliminary reports of waning effectiveness of the same vaccine have come from a health maintenance organization in Israel(10) and from the United States,(11) and a decrease in vaccine-induced neutralization titers during the first 6 months after receipt of the second dose of vaccine has been reported.(12)
"Abstract
In December 2020, Israel began a mass vaccination campaign against coronavirus disease 2019 (Covid-19) by administering the BNT162b2 vaccine, which led to a sharp curtailing of the outbreak.
After a period with almost no cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, a resurgent Covid-19 outbreak began in mid-June 2021.
Possible reasons for the resurgence were reduced vaccine effectiveness against the delta (B.1.617.2) variant and waning immunity.
The extent of waning immunity of the vaccine against the delta variant in Israel is unclear.
... Results
Among persons 60 years of age or older, the rate of infection in the July 11–31 period was higher among persons who became fully vaccinated in January 2021 (when they were first eligible)
than among those fully vaccinated 2 months later, in March (rate ratio, 1.6; 95% confidence interval [CI], 1.3 to 2.0).
Among persons 40 to 59 years of age, the rate ratio for infection among those fully vaccinated in February (when they were first eligible), as compared with 2 months later, in April, was 1.7 (95% CI, 1.4 to 2.1).
Among persons 16 to 39 years of age, the rate ratio for infection among those fully vaccinated in March (when they were first eligible), as compared with 2 months later, in May, was 1.6 (95% CI, 1.3 to 2.0).
The rate ratio for severe disease among persons fully vaccinated in the month when they were first eligible, as compared with those fully vaccinated in March, was 1.8 (95% CI, 1.1 to 2.9) among persons 60 years of age or older
and 2.2 (95% CI, 0.6 to 7.7) among those 40 to 59 years of age; owing to small numbers, the rate ratio could not be calculated among persons 16 to 39 years of age.
Figure 1. Figure 1. Daily Confirmed SARS-CoV-2 Infections and New Cases of Severe Covid-19 among Fully Vaccinated Persons in Israel, June through Early August 2021.
Israel conducted a very successful vaccination campaign using the BNT162b2 vaccine.(13), (14), (15)
Starting in December 2020, more than half the adult population received two doses of vaccine within 3 months.
... By May 2021, infection rates had decreased to a few dozen cases daily, most of which were in unvaccinated persons or in persons returning from abroad.
However, the number of polymerase-chain-reaction (PCR) tests that were positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) started to rise exponentially in June 2021, with a substantial number of infections being reported in vaccinated persons (Figure 1).
This rise in community transmission was followed by a concomitant increase in the numbers of severe cases and deaths, in both the vaccinated and unvaccinated populations.
Genetic analysis showed that as of June 2021, more than 98% of the positive cases in Israel were attributed to the delta variant.(16)
In this study, we estimated the role of waning immunity in the observed breakthrough against the delta variant.
Methods
... Only persons 40 years of age or older were included in the analysis of severe disease because severe disease was rare in the younger population.
Severe disease was defined as a resting respiratory rate of more than 30 breaths per minute, oxygen saturation of less than 94% while the person was breathing ambient air, or a ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen of less than 300.14 Persons who died from Covid-19 during the follow-up period were included in the study and categorized as having had severe disease.
... mThe official vaccination regimen in Israel involved the administration of the second dose 3 weeks after the first dose. All residents 60 years of age or older were eligible for vaccination starting on December 20, 2020, thus becoming fully vaccinated starting in mid-January 2021.
... if they did not belong to a designated group, persons 40 to 59 years of age received the second dose starting in mid-February, and those 16 to 39 years of age received the second dose starting in the beginning of March.
... Vaccinated persons were found to be protected even after 6 months, as compared with unvaccinated persons.
However, vaccine effectiveness was considerably lower than it had been closer to the vaccination date.
... This article was published on October 27, 2021, at NEJM.org.
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