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Covid-19: Vaccination plus infection offers best protection, finds study led by WHO

BMJ 2023; 380 doi: https://doi.org/10.1136/bmj.p171 (Published 23 January 2023) Cite this as: BMJ 2023;380:p171
  1. Ingrid Torjesen
  1. The BMJ

“Hybrid immunity” derived from a mix of infection by SARS-CoV-2 and vaccination provides higher protection against reinfection than vaccination or infection alone, shows a systematic review published in Lancet Infectious Diseases.1 Its findings highlight the protective benefits of vaccination even after people have had covid-19.

Although, at 12 months from the beginning of assessment, protection against reinfection fell quickly to 41.8% (95% confidence interval to 31.5% to 52.8%), protection against hospital admission or severe disease remained high.

The findings showed that people with hybrid immunity were well protected from hospital admission or severe disease a year later with lesser but still substantial protection against reinfection. Protection against hospital admission or severe disease was 97.4% (91.4% to 99.2%) at 12 months among patients with hybrid immunity who had received a primary series vaccination according to the vaccine manufacturers’ recommended schedule, and protection against reinfection was 41.8% (31.5% to 52.8%) in this group.

In contrast, among patients who had experienced a previous infection but had not been vaccinated, protection against hospital admission or severe disease was 74.6% (63.1% to 83.5%) and protection against reinfection was 24.7% (16.4% to 35.5%) at 12 months.

Data for the analysis came from 26 studies: 11 that reported the protective effectiveness of previous SARS-CoV-2 infection and 15 that reported the protective effectiveness of hybrid immunity.

Hybrid immunity was defined as infection and any vaccination in any order. Follow-up time started either two months after the last infection or after the time required for the most recent vaccination to be considered implemented as defined by the trials (typically 7-14 days).

The researchers said that their findings indicated a “substantial durability of hybrid immunity,” which could help inform the timing and prioritisation of vaccination programmes in populations with high rates of past infection.

“At the individual level, our results show that the need for, and optimal timing of, the primary vaccination series and booster dose might be different in an individual who has previously had SARS-CoV-2 infection or who has had a breakthrough infection after initiation of the primary series compared to a previously uninfected individual,” they wrote.

“Policy makers can use these findings to project population protection from local vaccination and seroprevalence rates, helping to inform the use and timing of covid-19 vaccination as an important public health tool.”

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