A study found that a double dose of Pfizer or Moderna offered almost 95% and 96% protection against contracting COVID-19 during the first two months.
It then fell to 67 and 80 percent after seven months.
Immunity after the second dose was found to wane after 20 weeks, especially for people over 65 years of age.
International researchers have said that a double dose still offers “strong protection” against hospitalization and death.
Pfizer has been shown to be over 94% effective in keeping teens from ending up in hospital.
US research has found that the Pfizer vaccine is 98% effective in preventing adolescents from ending up in intensive care.
The study also showed that a combination of AstraZeneca and Pfizer was more effective in neutralizing the Omicron variant than AstraZeneca alone.
Over 92% of Australians over 16 are now fully vaccinated.
How Australia coped with the emergence of the Omicron variant