AstraZeneca advice has just changed (again). Here's what you need to know if you're in lockdown
- Written by Nicholas Wood, Associate Professor, Discipline of Childhood and Adolescent Health, University of Sydney
Sydney’s COVID outbreak has just prompted official advice on the AstraZeneca vaccine to change to encourage more people to get fully vaccinated sooner.
Now, the Australian Technical Advisory Group on Immunisation (ATAGI) recommends people in outbreak areas have their booster shot at 4-8 weeks after their initial dose rather than wait for 12 weeks. ATAGI now also advises people in outbreak areas under 60 to “re-assess the benefits to them and their contacts” from getting an AstraZeneca vaccine now if the Pfizer vaccine is not available.
Advice for people outside outbreak areas remains unchanged.
Here’s how to make sense of the latest advice if you’re in an outbreak area.
The situation has changed
Getting vaccinated, like taking any medication, is a case of balancing the risks against the benefits. And clearly, when there’s a COVID outbreak such as Sydney’s, the potential benefit of vaccination just increased.
We know two doses of AstraZeneca vaccine (or the Pfizer vaccine) are really good at preventing you from serious disease and hospitalisation. There’s growing evidence COVID vaccines also reduce your chance of infecting others. And we know two doses are needed to improve your protection from the Delta variant, which is currently circulating in NSW.
Read more: Should I get my second AstraZeneca dose? Yes, it almost doubles your protection against Delta
Now let’s turn to the AstraZeneca vaccine. In parts of Australia with low rates of (or no) community transmission, the advice remains to wait 12 weeks after your initial dose for your booster shot. This is the time needed for your body to mount the best immune response.
However, as case numbers in Sydney have climbed, we’ve had calls from Prime Minister Scott Morrison, NSW Chief Health Officer Kerry Chant and Australia’s Chief Medical Officer Paul Kelly for people in outbreak areas to bring forward their AstraZeneca booster shots. Now ATAGI joins them.
Will I be protected if I go early?
Leaving less than 12 weeks between your first and second doses of AstraZeneca is a trade-off. There is slightly lower vaccine effectiveness against serious disease compared to if you’d waited for the full 12 weeks, but you will have some protection. In an outbreak, some reasonable protection now may be better than remaining unprotected while hanging out for greater immunity later.
The difficulty is pinning down exactly how much the vaccine’s efficacy drops by going early. The only figures we have that chart the different lengths of time between AstraZeneca shots and the corresponding levels of vaccine efficacy come from earlier variants of the virus (before Delta). We don’t actually have the figures as they relate to the Delta variant, circulating in NSW right now.
With that caveat in mind, here’s the best data we have about how different gaps between first and second dose of AstraZeneca affect its efficacy. It’s the same data ATAGI has cited to explain its latest advice.
Authors: Nicholas Wood, Associate Professor, Discipline of Childhood and Adolescent Health, University of Sydney