1. Two doses of Pfizer-BioNTech vaccine were associated with short-term protection against SARS-CoV-2 infection.
2. Infection-acquired immunity plus vaccination provided high protection for more than 1 year after SARS-CoV-2 infection.
Evidence Rating Level: 1 (Excellent)
Study Rundown: The duration of protection against SARS-CoV-2 infection via vaccines with respect to symptomatic and asymptomatic Covid-19 infection remains uncertain. There is a gap in knowledge as to understanding the protective durability and level of vaccines against SARS-CoV-2 after two doses of the Covid-19 vaccine in participants without and with the previous infection. This study found that two doses of the Covid-19 vaccine were associated with a significantly reduced risk in Covid-19 infection for about 6 months. Moreover, it found that patients with previous Covid-19 infection boosted with vaccination had the highest and most durable protection for more than 1 year. This study was limited by the relatively small number of participants who contributed follow-up data on key vaccination exposures. Nevertheless, these study’s findings are significant, as they demonstrate that two doses of the Covid-19 vaccine can provide 6 months of durable protection whereas previous infection plus vaccination provides the longest and most resilient protection against Covid-19 infection.
Click to read the study in NEJM
Relevant Reading: Effectiveness of the BNT162b2 Vaccine after Recovery from Covid-19
In-Depth [prospective cohort study]: This prospective cohort study studied 35,768 asymptomatic health care workers in the United Kingdom who agreed to undergo routine PCR testing. Participants were included if they underwent PCR testing and completed questionnaires every 2 weeks. Patients who did not undergo PCR testing in the follow-up periods, or if they had received vaccines other than the Pfizer-BioNTech or AstraZeneca vaccines, were excluded from the study. The primary outcome was PCR-confirmed SARS-CoV-2 infection, irrespective of the symptom status. This was defined as two PCR-positive samples >=90 days apart or a new PCR-positive sample >=28 days after an antibody-positive result consistent with the previous infection. Outcomes in the primary analysis were assessed via the Cox regression model with adjustment for factors such as previous infection status, vaccine type, dosing interval, demographics, and workplace exposure. Based on the analysis, two doses of the Pfizer-BioNTech vaccine provided a decrease in risk of infection of 85% (95% confidence interval [CI], 72 to 92) in the first 2 months, and 14-73 days after the second dose. The adjusted vaccine effectiveness was 68% (95% CI, 54 to 77), 134-193 days after the second dose. In those participants who were previously infected but received appropriate vaccination afterward, the risk of reinfection was 86% lower (95% CI, 81 to 89) compared to unvaccinated participants, with the waning of protection in 1 year after infection with a reduction to 69% protection during the first year after infection (95% CI, 38 to 84). Overall, this study demonstrated that vaccination with the Pfizer-BioNTech vaccine provided high durable protection against Covid-19 infection for 6 months, while the previous infection boosted with one or two doses of vaccine provided up to 1 year of durable protection. This can inform future vaccination scheduling to avert waning of protection and ensure continued reduction in the infection rates and transmission of Covid-19.
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