What you need to know about the coronavirus right now

Sydney seeks to tighten curbs, Canberra to enter lockdown
Extra Australian military personnel may be called in to ensure compliance with lockdown rules in Sydney, the New South Wales state government said on Thursday, as the highly infectious Delta coronavirus variant spreads into regional areas. Some 580 unarmed army personnel are already helping police enforce home-quarantine orders on affected households in the worst-affected suburbs of Sydney, Australia's most populous city.

The move comes as Australia's capital, Canberra, 260 km (160 miles) southwest of Sydney, announced a snap one-week lockdown from Thursday evening after reporting its first locally acquired case of Covid-19 in more than a year.

Fortress New Zealand eyes opening to vaccinated travellers
New Zealand plans to allow quarantine-free entry to vaccinated travellers from low-risk countries from early 2022, as it looks to open its borders again after nearly 18 months of pandemic-induced isolation.

Prime Minister Jacinda Ardern said on Thursday that the country is still not ready to open up entirely, but will open in phases from early next year. Despite the phased reopening, the government will stay on its elimination strategy to maintain its hard-won gains as one of the few virus-free countries, Ardern said.

Asymptomatic Covid-19 very common
Roughly a third of people with Covid-19 have no symptoms, according to a review of data from more than 350 studies published through April 2021. Asymptomatic infections were more common in children than in the elderly or in people without preexisting medical conditions, said Pratha Sah of the Yale School of Public Health, who led the analysis published on Tuesday in PNAS.

Her team estimates that 46.7% of infected children have no symptoms, she said. "This is especially concerning because settings with close, extensive contact among large groups of younger individuals are particularly susceptible to superspreader events of Covid-19, which may go undetected" if school authorities only watch for symptoms. Senior author Alison Galvani, also of the Yale School of Public Health, noted that asymptomatic individuals can still pass the virus to others.

U.S. FDA set to authorize vaccine boosters for immunocompromised
The U.S. Food and Drug Administration is expected to authorize a third booster dose of Covid-19 vaccines by Pfizer Inc and Moderna Inc for people with weakened immune systems, NBC News reported on Wednesday.

The health agency will amend the emergency use authorizations for the two vaccines as soon as Thursday to allow immunocompromised people to get an additional dose, the report said, citing people familiar with the matter.

EU looking into new possible side-effects of mRNA shots
Three new conditions reported by a small number of people after vaccination with Covid-19 shots from Pfizer and Moderna are being studied to assess if they may be possible side-effects, Europe's drugs regulator said on Wednesday.

Erythema multiforme, a form of allergic skin reaction; glomerulonephritis or kidney inflammation; and nephrotic syndrome, a renal disorder characterised by heavy urinary protein losses, are being studied by the safety committee of the European Medicines Agency (EMA), according to the regulator.