This is an excerpt from an article which was first published on the ABC News website. Click to read the article in full.
Australia's Therapeutic Goods Administration (TGA) has given the green light to the AstraZeneca COVID-19 vaccine paving the way for it to be given to millions of Australians.
Australia has secured 53.8 million doses of the AstraZeneca vaccine, 50 million of them to be made locally by CSL. Most Australians are expected to receive this vaccine rather than the Pfizer vaccine when its rollout begins in late March.
In its detailed analysis, the TGA said AstraZeneca had shown to be safe and prevent COVID-19, the disease caused by the coronavirus, but it was not clear yet whether it prevented transmission or asymptomatic disease.
Ahead of its expected rollout from March, the TGA advised that the AstraZeneca jab should be administered in two doses 12 weeks apart.
That came after a study in The Lancet released this month - which is yet to be peer reviewed - showing the vaccine had 76 percent efficacy after one jab.
It found that increased to 82 percent after a booster jab was given three months later.
How long do vaccinations usually remain effective?
There's no 'typical' timeframe that a vaccine will protect us for - it's different for every vaccine.
To recap, vaccines help your develop an immunity to a virus without you having to contract it and get sick.
"Most vaccines, and we hope the COVID vaccine, produce a much higher level of immunity than natural infection," Burnet Institute epidemiologist, Professor Mike Toole AM said.
But not all vaccines do this in the same way or protect us for the same period of time.
The two-dose measles-mumps-rubella (MMR) vaccine, for example, contains a weak, live version of the viruses and works so well that it offers lifelong protection.
"Measles - the protection is lifelong, smallpox lifelong, other vaccines needs boosters after a while, typhoid fever, hepatitis," Professor Toole said.
How long will the COVID-19 vaccines remain effective?
It's too early to tell. There's a lot more research about the efficacy of COVID-19 vaccines - meaning how well a vaccine prevents someone from getting the virus - than about the lifespan of the vaccines themselves.
Professor Toole said we simply don't know how long the COVID-19 vaccines will last - although we may have a clearer picture by mid-year.
"That's the short and only answer really because we just don't know," Professor Toole said.
"We haven't been rolling out the vaccine long enough to monitor how long and how well it protects people from infection."
Why do some vaccines need a booster and others don't?
This depends on how our bodies respond to the vaccine. For example, the MMR vaccine offers lifelong protection against measles.
Professor Toole said this is because live vaccines are "more or less the same as being infected" and it's been proven that people don't get measles twice.
Measles is also a stable virus and doesn't mutate - unlike COVID-19, which has already evolved into different variants.
If the Pfizer and AstraZeneca COVID-19 vaccines don't last long, Professor Toole says the most "likely outcome" is we'll need a booster jab or an annual shot that's adapted to fight off different variants.
Will I feel sick after the COVID-19 vaccine?
According to clinical trials, yes, you may feel a bit unwell after the jab - especially after the second one.
The US Centers for Disease Control describes these as "normal signs that your body is building protection".
Think of it as a positive sign - the vaccine is doing what it's meant to and helping your body develop immunity to the virus.
"In around about one in 10 people who receive the vaccine, they'll get soreness, redness at the site of the injection, plus maybe a low fever or a headache," Professor Toole said.
"One in 100 will get more severe side-effects after the second dose - nausea, poor appetite - maybe some gastric upset."
It's also important to remember these side effects are temporary, most last no more than a couple of days and patients recover without any problems.
Will the Pfizer or AstraZeneca vaccine protect from COVID-19 straight away?
No. You will need two doses of the vaccine to be properly protected.
And it's worth remembering that the vaccine won't necessarily stop you from getting COVID-19 and spreading it, but will help your body not to get sick if you do contract it.
