Do not recommend mixing Covid-19 vaccines, says UK health agency

Following the Britain government’s new guidelines regarding interchangeability of different Covid-19 vaccines from different manufacturers, UK health agency Public Health England (PHE) has said that it does not recommend mixing different vaccines.

Commenting on reports on mixing vaccines, Dr Mary Ramsay, Head of Immunisations at PHE, said, “We do not recommend mixing the COVID-19 vaccines – if your first dose is the Pfizer vaccine you should not be given the AstraZeneca vaccine for your second dose and vice versa.”

"There may be extremely rare occasions where the same vaccine is not available, or where it is not known what vaccine the patient received. Every effort should be made to give them the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all," added Dr Ramsay.

The Britain government in its recent guidance to public health practitioners regarding Covid-19 vaccination has allowed for the interchangeability of different Covid-19 vaccines. The government so far has approved the emergency use of two Covid-19 vaccines, that by Pfizer and BioNTech along with the vaccine developed by AstraZeneca and Oxford University.

“For individuals who started the schedule and who attend for vaccination at a site where the same vaccine is not available, or where the first product received is unknown, it is reasonable to offer a single dose of the locally available product,” reads the updated guidance.

“This option is preferred if that individual is likely to be at immediate high risk or is considered unlikely to attend again. In these circumstances, as both the Pfizer-BioNTech and AstraZeneca vaccines are based on the spike protein of the virus, it is likely that the second dose will help to boost the response to the first dose,” it adds.

However, the guidance also adds, “There is no evidence as to the interchangeability of the different COVID-19 vaccines although studies are underway. Therefore, every effort should be made to determine which vaccine the individual received and to complete with the same vaccine.”

Many health experts have warned against the mixing and matching of different vaccines, calling it a “gamble” as per media reports.

Steven Danehy, a spokesman for Pfizer said, “While decisions on alternative dosing regimens reside with health authorities, Pfizer believes it is critical health authorities conduct surveillance efforts on any alternative schedules implemented and to ensure each recipient is afforded the maximum possible protection, which means immunization with two doses of the vaccine,” as quoted by a New York Times report.

Both Pfizer’s and AstraZeneca’s vaccines introduce spike protein into the body to generate a n immune response. Pfizer’s vaccine is based on a molecule called messenger RNA, or mRNA while AstraZeneca’s vaccine is designed around a virus shell that delivers DNA, a cousin of mRNA, as per the report.

Britain also sparked a controversy earlier this week with its decision to front load to deliver first doses to as many people as possible. This could delay the administration of the second dose up to 12 weeks, as per the NYT report.

Top infectious diseases expert in the United States, Anthony Fauci disagreed with the approach.

“I would not be in favour of that,” he told CNN. “We’re going to keep doing what we’re doing.”

The US Centers for Disease Control and Prevention in its guidance has said that different vaccines “are not interchangeable.” “The safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product,” it said.