Study suggests mixing vaccines offers strong immune protection
WHO cautions against the practice due to limited long-term data
NASSAU, BAHAMAS — As The Bahamas awaits a tranche of Pfizer doses from the World Health Organization’s (WHO) COVAX Facility and could offer recipients of AstraZeneca a second dose of the US-manufactured vaccine, studies have shown that vaccine mixing offers strong immune protection.
In a recent interview with Eyewitness News, Minister of Health Renward Wells pointed to existing studies where mixing of AstraZeneca and Pfizer were found to have been “very effective”, though he did not definitively say whether The Bahamas would adopt the measure.
According to the preliminary results of the CombivacS Spanish study, the presence of antibodies in the bloodstream was between 30 and 40 times higher in people who got the follow-up Pfizer shot than others in the control group, who only received one AstraZeneca dose.
The presence of neutralizing antibodies rose sevenfold after a Pfizer dose — more than double the effect observed when receiving a second dose of AstraZeneca.
Nearly 700 volunteers between the ages of 18 and 59 participated in the state-backed study, with around 450 given a Pfizer dose.
The World Health Organization has said public health agencies, and not individuals, should make decisions on mixing and matching COVID vaccines, based on available data.
The government of Vietnam announced on Monday that it will offer the coronavirus vaccine jointly developed by Pfizer as a second-dose option for individuals who were first inoculated with AstraZeneca.
It said Pfizer will be prioritized for people who were given a first shot of AstraZeneca eight to 12 weeks before.
Other countries have adopted a similar approach.
Canada, Spain and South Korea have approved dose-mixing due to concerns about rare but possible blood clots linked to the AstraZeneca vaccine.
Amid concerns about COVID variants, including the Delta strain, Wells said the vaccines have proven effective against all five variants of concern, maintaining that it is not a matter of if but when the Delta variant is confirmed in The Bahamas.
The government of The Bahamas is expected to receive more than 57,000 doses of Pfizer through the COVAX Facility.
It had exclusively received AstraZeneca COVID-19 vaccine doses through COVAX since the vaccine rollout began earlier this year.
The Bahamas is also expected to receive a balance of 33,600 AstraZeneca doses from COVAX on July 26, according to the health minister.
The US is also slated to donate a tranche of AstraZeneca doses from its surplus, though quantity and dates have yet to be announced.
As of July 10, more than 97,992 vaccine doses had been administered in The Bahamas, with 60,303 people receiving a first dose of the vaccine and 37,689 fully vaccinated.
There have been concerns about the availability of vaccine supplies in recent weeks with the number of administered doses exceeding The Bahamas’ supply of vaccine doses.
But Eyewitness News understands the disparity can be attributed to additional doses being drawn up from the AstraZeneca COVID-19 vaccine vial, giving 11 doses instead of 10 in some instances.
Each vaccine dose of 0.5 ml is withdrawn into a syringe for an injection to be administered.
Each vial contains at least the number of doses stated, but it has been normal for an additional 0.5 ml to remain in the vial.
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