Covid 19 coronavirus: Small number will still get virus after vaccination, warns disease expert

Professor Peter Collignon said a small percentage of the vaccinated population would test positive for Covid-19 following their first and second doses of the vaccine. Photo / News Corp

An Australian infectious disease expert has warned a small number of people will still get Covid-19 even after being vaccinated as New South Wales health officials scramble to determine how a hotel quarantine security guard contracted the virus 10 days after getting his first Pfizer jab.

The guard works at two quarantine hotels in Sydney and tested positive for the UK strain of Covid-19 on Saturday night after contracting it from a returned traveller staying at the Sofitel Wentworth. He then worked at the Mantra quarantine hotel on Friday while infectious and contact tracers are scrambling to reach out to all colleagues who worked the night shift with him. It is the state's first local case in 55 days.

NSW chief health officer Dr Kerry Chant said although the security guard worked on the same floor as the infected returned traveller, he adhered to Covid-safe measures, which has left health officials stumped as to how the guard contracted the virus.

"This gentleman was exemplary in his adherence to the procedures for mask wearing and other protections and precautions. So we haven't been able to find an exact source or explanation for how this person became infected," Chant said.

Although the man received a first dose of the Pfizer vaccine on March 2 and was awaiting his second jab, infectious diseases expert Peter Collignon suggests that a small percentage of the vaccinated population will still test positive for Covid-19 following their first and second doses of the AstraZeneca or Pfizer vaccines.

But it is still better than not getting the jab at all, according to Collignon.

"The reason this particular individual [security guard] or any individual for that matter tested positive after a vaccination is firstly because the body takes 10 to 14 days after the jab to develop enough white cells to kill the virus," Collignon told NCA NewsWire.

"You don't get full protection after one dose, so it will not be surprising to see a small number of people get the virus after vaccination."

Sydney's Sofitel Wentworth is one of the quarantine hotels used by the NSW Government to house returned travellers. Photo / News Corp

"One dose does give a person protection, but having two doses is even better," Collignon said.

"However, that number of vaccinated people who will contract the virus will still be lower than if they didn't get the vaccine. The vaccine will reduce the spread and severity of the disease. Nothing is absolute, anyway; two does of any vaccine does not make you completely impervious to the virus. But it is highly effective."

NSW Premier Gladys Berejiklian. Photo / Getty Images

NSW Premier Gladys Berejiklian, speaking today to reporters about the state's new local case, said it was inevitable that leaks would occur in hotel quarantine.

"I wasn't commenting yesterday on this, but I will say while it is always concerning to have a case outside of overseas travellers, it is not surprising; we always know it is a high risk," she said.

"However, let's not overreact. It is just the one case."