Coronavirus infections in fully-vaccinated people are rare but are more common and severe in people with weaker immune systems, a new study has suggested.
Researchers analysed healthcare records and found that only 0.08% of people in their fully-vaccinated pool experienced a breakthrough infection between December 10, 2020 and July 8, 2021.
They also found that while immunocompromised individuals represented 18% of those studied, they accounted for more than 38% of infections, nearly 60% of all hospital admissions, and 100% of deaths.
According to the study, the proportion of people with breakthrough infections was three times higher among immunocompromised individuals (0.18%) than among the reference group of non-immunocompromised people (0.06%).
Manuela Di Fusco, lead author from the Pfizer Health economics and outcomes research team, said: â€œThe results supplement other real-world studies and support the introduction of a third dose of a Covid-19 vaccine to increase protection among the immunocompromised individuals.
â€œSeveral countries are currently experiencing a resurgence of Sars-CoV-2 infections despite the rollout of mass vaccination programmes.
â€œWhile Covid-19 mRNA vaccines help protect people from getting infected and severely ill, the risk of breakthrough infections in fully-vaccinated people is not completely eliminated.â€
Identifying individuals in the US population who had received two doses of the Pfizer/BioNTech vaccine, the Pfizer study looked to examine breakthrough infections among those with and without a weakened immune system.
The team analysed healthcare records of 1,277,747 people aged 16 or over who had received two doses of the jab.
In this group, 225,796 (17.7%) were identified as immunocompromised â€“ including people with advanced HIV/Aids, cancer, kidney disease, rheumatologic or other inflammatory conditions, other immune conditions, and bone marrow or organ transplant recipients.
Ms Di Fusco added: â€œOur study results advance the understanding of post-vaccination outcomes and support recent recommendations to provide a third primary series dose of an mRNA Covid-19 vaccine to patients with weaker immune systems after the initial two doses.â€
The findings come as the UKâ€™s Joint Committee on Vaccination and Immunisation (JCVI) announced that severely immunosuppressed people should be offered a booster dose no sooner than three months after completing their primary course of three doses.
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