Covid infections rare in fully vaccinated but more common and severe in those with weaker immunity

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UKRAINE - 2021/09/07: In this photo illustration a medical syringe and vials are seen displayed in front of the Booster dose and Covid-19  text. (Photo Illustration by Pavlo Gonchar/SOPA Images/LightRocket via Getty Images)
UKRAINE - 2021/09/07: In this photo illustration a medical syringe and vials are seen displayed in front of the Booster dose and Covid-19 text. (Photo Illustration by Pavlo Gonchar/SOPA Images/LightRocket via Getty Images)
SOPA Images / Contributor
  • A study investigated breakthrough infection risk in people with compromised immune systems.
  • The study involved a large cohort of 1.2 million fully vaccinated people.
  • The results of the study encourage a third Pfizer vaccine dose for immunocompromised people.

Covid-19 vaccine breakthrough infections are rare on the whole, but have been found to be more common and severe in immunocompromised people, according to a new study.

The study published in the Journal of Medical Economics evaluated how Covid-19 breakthrough infections happen in immunocompromised people.

The researchers gathered data from the US HealthVerity database of more than 1.2 million fully vaccinated people (with the Pfizer vaccine) between 10 December 2020 and 8 July 2021. They divided the cohort between people who are immunocompromised and those who have fully functional immune systems.

People with Covid-19 breakthrough infections were examined a minimum of 14 days after their second vaccine dose.

The immunocompromised condition group included people with HIV; solid malignancy; bone marrow transplant; organ transplant (excluding bone marrow transplant); primary immunodeficiency; chronic kidney disease or end-stage renal disease; and hematologic malignancy.

The higher breakthrough infection risk

The study found that only 0.08% of the 1.2 million participants had a breakthrough infection. Of this percentage, immunocompromised people accounted for more than 38% of infections, almost 60% of all hospitalisations, and 100% of deaths.

Immunocompromised people had three times more breakthrough infections than people without such conditions.

In the immunocompromised group, people with primary immunodeficiencies and hematologic malignancies also had higher breakthrough incidence rates than the rest of the cohort.

Waning protection and emerging variants

The researchers say that the study results show the need for people with compromised immune systems to get a third (booster) Covid-19 vaccine dose.

“Our conclusions support the FDA authorisation and CDC recommendations to offer a third vaccine dose to increase protection among immunocompromised individuals, and the need for vigilant efforts to maximise vaccine uptake among the immunocompromised, especially in the context of the waning duration of protection and emerging SARS-CoV-2 variants.

"Moreover, our findings suggest that breakthrough infections can occur regardless of active treatment status in the immunocompromised and that there may be additional vulnerable IC groups that could benefit from increased protection,” the authors wrote.

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