Delaying the second dose of Pfizer’s vaccine could be dangerous, immunologist warns

An immunologist at the University of Queensland has cautioned over the UK’s decision to delay second doses of the Pfizer vaccine, claiming the move could create a breeding ground for further COVID-19 mutations.

The UK initially planned to administer Pfizer vaccine recipients with the full two doses required for maximum efficacy, within 21–28 days. More recently, it has opted to double its immediate rollout of single vaccine doses with a view to giving wider spread, albeit weaker, virus protection in the short term.

However, Dr Larisa Labzin says that this ‘quantity over quality’ approach to immunisation may be dangerous if people go back to normal routine after just one dose.

“One dose of the Pfizer vaccine is only about 50% protective, meaning the virus can still infect people and make them sick,” Dr Labzin said.

“Worse still, that insufficient level of immunity in the one-dose vaccine recipient might create just enough ‘selective pressure’ within their body for the virus (should they be exposed to it) to fight back and develop mutations. This is something viruses do to try and escape vaccine-induced immunity. By contrast, administering two vaccine doses in quick succession induces an immune response strong enough to completely eliminate the virus from the recipient’s body before the virus has a chance to adapt.

“By introducing an insufficient dosage of the vaccine, you are essentially giving the virus a ‘workout’ and an opportunity to grow ‘fitter’ by adapting and developing mutations,” Dr Labzin continued.

“If a person that has only received a single dose of the vaccine gets exposed to COVID-19, it may only be a matter of time before we start seeing more resilient strains of the virus, similar to what we see with influenza virus. These strains could overcome vaccine-induced immunity, and mean that we might need to update the COVID vaccine, like we do for flu each year.”

However, there isn’t yet enough epidemiological data to confirm whether the gamble taken by Public Health England will pay off.

“Viruses can also mutate when they are given an opportunity to replicate in a large pool of people. It may be that giving more people a lower dosage of the Pfizer vaccine reduces the virus’s ability to circulate the population and adapt,” Dr Labzin added.

In the absence of data, the best bet is to continue with strict hygiene and social distancing measures, in conjunction with the vaccination program.

“If we can physically prevent spread of the virus then we can drastically reduce its ability to replicate and mutate,” Dr Labzin said.

“Additionally, developing host-directed therapies, like antivirals and anti-inflammatories, that lessen the time someone remains ill with COVID-19 may also be a great help,” she concluded.

Image credit: ©stock.adobe.com/au/Feydzhet Shabanov