Covid-19 vaccine: Large study supports third Pfizer jab for immunocompromised

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  • People with weakened immune systems are at high risk of severe Covid-19.
  • The latest research, supported by earlier studies, found that vaccine efficacy is reduced in this group.
  • Some countries have started offering a third dose to the immunocompromised for better protection.

A third dose of the Covid-19 Pfizer-BioNTech is likely to benefit people with immunocompromised conditions (IC). This is according to a Pfizer-funded study that assessed breakthrough infections in this group.

Having an IC or a weakened immune system can make one more susceptible to severe Covid-19, according to the US Centers for Disease Control and Prevention (CDC). While immunodeficiency can be due to inherited genetic defects, certain conditions and treatments (such as chemotherapy for cancer) can also cause a weakened immune system. 

“People who have a condition or are taking medications that weaken their immune system may not be protected even if they are fully vaccinated,” the agency states.

Researchers of the latest study, which appears as a preprint on the medRxiv* server, assessed the incidence of breakthrough infections (an infection that occurs after being fully vaccinated) among immunocompromised people (versus a control group). The study focused especially on those on active immunosuppressive medication. 

Study results

According to study findings, out of approximately 1.2 million fully vaccinated individuals over the age of 16 years, about 18% were immunocompromised (with a median age of 58 years).

Almost 63% of those with an IC had more than one condition putting them at high risk of severe Covid, while less than a fifth of those with normal immune systems had underlying conditions.

Highest among organ transplant recipients

Studying the period from December 2020 to early July 2021, the researchers found that there were 978 breakthrough infections – of which 374 were in immunocompromised patients. Importantly, the risk of breakthrough infection was three times higher in the IC group compared with the non-IC group. 

A total of 74 (19.8%) of these patients were hospitalised. Nine of them required  invasive mechanical ventilation and 23 were admitted to the ICU. Two patients died.

“While individuals in the IC cohort only represented approximately 18% of the fully vaccinated population, they accounted for 38.2% of all breakthrough infections, 59.7% of all hospitalisations, and 100% of inpatient deaths,” the authors wrote.

The incidence rate of breakthrough infections was highest among organ transplant recipients (excluding bone marrow transplant recipients), they noted. 

“While some Covid-19 vaccine breakthrough infections among those who are fully vaccinated against Covid-19 are expected, the findings of this study show that they are rare and less likely to result in hospitalisation or death in those without an IC condition,” the researchers wrote.

Findings supported by earlier studies

The study, which has not yet been peer-reviewed, is the largest one to look at breakthrough infections following full vaccination among immunocompromised individuals.

The findings are also supported by those of other recent real-world studies indicating reduced vaccine protection for some IC patient groups.

The team concluded: “The study findings show that breakthrough infections are rare but are more common and severe in people with certain IC conditions. 

“They support FDA (Food and Drug Administration) authorisation and CDC recommendations to offer a third vaccine dose to increase protection among IC individuals, and the need for vigilant efforts to maximise vaccine uptake among the IC, especially in the context of a waning duration of protection and emerging SARS-CoV-2 variants.”

SA will also offer third dose

South Africa’s health department has followed suit – last week, health minister Joe Phaahla announced that the department had been advised by the Vaccine Ministerial Advisory Committee (VMAC) that people who have compromised immunity should receive an additional vaccine dose.

This will include people who are on long-term oral steroids therapy for autoimmune conditions, those who have haematological or immune malignancies, and those who have had solid organ or bone marrow transplants, renal dialysis and primary immunological disorders, News24 reported.

"The advice is that these categories of patients be offered an additional dose over the prescribed normal, but this must be strictly under the referral by their medical doctor under their supervision," Phaahla said.

*For more Covid-19 research, science, and news, click here. You can also sign up for our Daily Dose newsletter here.

READ | Covid-19 infections that persist in people with weakened immune systems may give rise to new variants

READ | How will Covid vaccines work on compromised immune systems? Here’s what we know

READ | Long Covid: More than 50% of people who survive infection will experience lingering symptoms – study

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