The state is the last to bring down its hard border but some travel restrictions remain in place, including the requirement for people to be triple vaccinated and complete a travel pass to enter.
The reopening comes after Premier Mark McGowan delayed easing border regulations earlier this year due to rising Omicron cases across Australia.
WA Police Commissioner Chris Dawson said he expected an influx of travellers with almost 23,000 travel applications as of Wednesday morning.
One of those will be Labor leader Anthony Albanese, who has been eager to campaign in WA ahead of the federal election.
Getting a third dose will also be easier for people who can't receive an mRNA vaccine like Pfizer, with the Australian Technical Advisory Group on Immunisation recommending the Novavax vaccine be used as a booster.
The advisory group said Novavax was recommended for those over 18 when an mRNA vaccine is not suitable.
Health Minister Greg Hunt said since Novavax was first approved by the country's medical regulator, more than 25,000 doses of the vaccine have been administered as a first dose.
Meanwhile, Prime Minister Scott Morrison remains in isolation after contracting COVID-19.
There have more than 60 deaths reported from COVID-19 on Wednesday, including 28 from Victoria, 24 in Queensland, five in NSW, two in South Australia and two in the Northern Territory.
More than 29,000 new infections were detected across the country, of which 10,650 were in NSW, 7126 in Victoria, 5011 in Queensland, 2075 in SA, 1780 in WA, 1053 in the ACT, 624 in the NT, and 868 in Tasmania.
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