The head of the World Health Organization (WHO) has said that while there is hope for a vaccine against Covid-19, one might never be found.
Tedros Adhanom Ghebreyesus told a news briefing there was "no silver bullet at the moment - and there might never be".
Mr Tedros implored people around the world to comply with measures such as social distancing, hand-washing and mask-wearing, saying: "Do it all."
Globally, more than 18 million Covid-19 infections have been recorded.
The death toll stands at 689,000, with both figures given by the US-based Johns Hopkins University.
Speaking from its headquarters in Geneva, the WHO chief said work on immunisation was progressing.
"A number of vaccines are now in phase 3 clinical trials, and we all hope to have a number of effective vaccines that can help prevent people from infection.
"However, there is no silver bullet at the moment, and there might never be," Mr Tedros warned. "For now, stopping outbreaks comes down to the basics of public health and disease control: testing, isolating and treating patients, and tracing and quarantining their contacts."
Mr Tedros said that mothers with suspected or confirmed coronavirus infection should be encouraged to continue breastfeeding.
The benefits, he said, "substantially" outweighed the risks of infection.
Meanwhile, the first stage of a WHO investigation into the possible source of the outbreak in China is now complete, he said.
Infectious disease experts believe the virus initially jumped from animals to humans and attention has focused on a wet market in the Chinese city of Wuhan, where the Covid-19 pandemic began.
An advance team probing the source has concluded its mission and will be followed by a larger WHO-led international group, including Chinese experts. It is not yet known when it will commence.
In other developments:
- The Australian city of Melbourne is shutting down shops, factories and other non-essential businesses as authorities fight a second wave of coronavirus. A night-time curfew has been imposed on the city's five million residents as part of measures to try to curb the spread of the disease.
- At least 41 passengers and crew on a Norwegian cruise ship have tested positive for Covid-19, officials say. Hundreds more passengers who travelled on the MS Roald Amundsen are in quarantine and awaiting test results.
- The number of deaths from coronavirus in Iran is nearly three times higher than Iran's government claims, a BBC Persian service investigation has found. The government's own records appear to show almost 42,000 people died with Covid-19 symptoms up to 20 July, compared to 14,405 reported by its health ministry.