What are the symptoms? 
A new infection of the Delta variant has slightly different symptoms to classic COVID-19, according to a UK researcher.
“Cough is rarer and we don’t even see loss of smell coming up in the top 10 anymore,” Prof Tim Spector of King’s College London said earlier this month.  
Instead, mild cases of the disease in young people present more like a bad cold, he says. The fear is people will think it’s just a cold and not get tested or isolate themselves, further spreading the virus. 
“The number one symptom is headache, followed by runny nose, sore throat and fever. Not the old classic symptoms… people don’t realise that and it hasn’t come across in any of the government information.
“This means that people might think they’ve got some sort of seasonal cold and they still go out to parties and might spread around to six other people and we think this is fuelling a lot of the problem.”
Is it deadlier than previous variants?
UK data suggests people infected with the Delta variant are twice as likely to end up in hospital than those who contract Alpha. 
Even if it turns out not to be deadlier, the WHO has warned Delta has the potential to kill more people “because it’s so infectious, and “will eventually find those vulnerable individuals who will become severely ill, have to be hospitalised and potentially die”, Mike Ryan, executive director of the WHO’s health emergencies programme, said earlier this week. 
Are vaccines effective against it? 
So far, the answer appears to be yes – but not as effective as they were against the original or other strains. 
The Pfizer-BioNTech vaccine being rolled out in New Zealand has been shown to be about 94 percent effective against the original strain, two weeks after the second dose. But data collected so far suggests a two-dose regime only offers 79 percent protection against infection with Delta – high enough that it’s still a wise move to get it, but a significant drop.
Data collected during Israel’s early and quick vaccine rollout suggested even a single dose of the Pfizer vaccine offered up to 85 percent protection against infection with original COVID-19, prompting some countries to roll out single doses to as many people as possible, rather than fully vaccinating fewer people. 
But newer research published at the end of May has found the Pfizer vaccine is only 33 percent effective against Delta after a single dose.