Health Editor Jill Margo seeks answers from the experts about enduring uncertainties about vaccines, the hunt for herd immunity and how to find out if you’ve had COVID.

This is a key question and the answer is not clear, says Professor Cheng.
It may depend on the type of vaccine. The Novavax vaccine, on order but not yet approved in Australia, is based on a traditional vaccine type.
Like shots given for flu, this old-fashioned protein vaccination can probably be given again, but whether and when this is needed, has to be studied.
With the Astra Zeneca/Oxford vaccine, you can get your two shots but, because of the way the vaccine is constructed, a third shot down the track may not be as effective.
He says it appears that the Pfizer vaccine can be given again, but it is brand new technology and needs to be tested to make sure this is correct.
Do we have to have herd immunity?
As we dont know if vaccines prevent transmission, we dont know if herd immunity is possible. Even if they do prevent it, but for a limited time, that would make herd immunity imperfect.
Not everyone will opt to get vaccinated, and some people, such as children, cant be vaccinated yet. Further, the vaccine may not work in people with weakened immune systems.
Professor Cheng says while it would be good to achieve herd immunity, vaccines will directly provide protection from illness which really is the primary aim of a vaccine program.
Nothing is perfect in public health. He says its a question of layers, and a layer of protection from illness conferred by a vaccine is a very good thing to have.
In pregnant women, will COVID-19 or treatments for it, put the baby at risk?
For pregnant women with COVID-19, it is possible the virus may pass to the baby during pregnancy, delivery or through breast milk, although this is rare. Currently, there is no evidence to suggest COVID-19 is cause for a caesarean section.
Associate Professor Joshua Vogel from Taskforce, says the use of masks and hand hygiene by women with COVID-19 when feeding or caring for the baby are important.
Women who develop severe COVID-19 might require admission to hospital where treatments used in non-pregnant adults with COVID-19 can be also used for them.
What will post-vaccine life look life?
Globally, the requirement for masks, hand washing and social distancing will remain for some time, says Adjunct Professor Heidi Drummer from the Burnet Institute.
Keeping our international borders closed in the immediate future will give us more security.
Israel and the UAE, with their high levels of vaccination, may soon help to answer questions about the effectiveness of vaccines in blocking transmission.
How to check if you actually did have COVID-19 last year?
If you think you may have had COVID-19 but didnt get a test, Dr Cheng says you can ask your GP for a serological test.
This laboratory blood test looks for antibodies to see if an infection has been and gone.
There are instant home tests available elsewhere in the world but many of these are unreliable.
Another swab test wont help because if the suspected infection was months ago, there may be no trace of virus left in your mucus.
When does a positive test mean no quarantine?
When you have recovered from COVID-19 and have some viral fragments floating around, but are not infectious, says Professor Cheng.
Fragments can be present for some time after recovery. Some people might have a couple of positive tests, then a couple of negatives and then another positive test.
Lingering positive tests may be due to shedding of fragments. Laboratories have a way of determining this, by looking at your past positive tests that showed an infection and how much virus appears to be present.
If the test is positive within eight weeks, it is generally considered to be shedding and youll be asked about symptoms and perhaps tested again.
Beyond eight weeks, there will be discussion about symptoms. You, and perhaps the people around you, may require tests to exclude re-infection.
Its a complicated process and an expert panel considers these cases.
What to do if you test negative but symptoms persist?
If you were in hospital and the clinical suspicion of you having COVID-19 was high, but your test was negative, youd likely be re-tested.
So, if you are at home, you could go for another swab test too.
These tests are sensitive and with two negatives, you can depend upon the result, says Professor Elliott, head of the The National COVID-19 Clinical Evidence Taskforce.
But guidelines suggest two tests is enough.
Will any medication reduce the chances of getting COVID-19?
There are two approaches here. One is taking a preventive medication at any time and the other is taking it after youve been exposed to the virus.
The Taskforce says there is no evidence that anything helps.
This kind of protection is called chemoprophylaxis, and so far, it has been tested in five randomised controlled trials with no positive results.
Do steroids affect your chances of dying from COVID-19?
There is now very strong evidence that treatment with corticosteroids (like those given for conditions such as asthma, not body building steroids) reduce the risk of dying in those with more severe COVID-19.
“If you are already on steroids, and get COVID-19, you should continue, as these medications are important for your overall health and it is likely you would be worse off if they were stopped,” says Professor Elliott.