Millions of children could die from preventable disease because of severe disruptions to vaccination programmes caused by coronavirus, experts warn.
At least 68 countries have been affected - with some stopping vaccination campaigns completely.
The World Health Organization advised many countries to suspend vaccinations to help slow the spread of coronavirus.
But now it is one of several groups expressing concern about the long-term impact.
United Nations Children's Fund (Unicef), the Sabin Vaccine Institute and Gavi, the Vaccine Alliance are also worried thousands of children every day could die needlessly.
There are a number of reasons vaccination services have been so badly disrupted, including:
- parents' fear of catching Covid-19 if they leave the house
- health workers being diverted to deal with the pandemic
- problems getting vaccine supplies to clinics
"Measles is on the rise, diphtheria, cholera," United Nations Children's Fund (Unicef) executive director Henrietta Fore says.
"So this is going to be a real problem.
"As a world, we had conquered many of these preventable diseases for children."
Now, there are grave concerns these gains could be "wiped away".
In a usually packed clinic in Niger's capital, Naimey, the waiting room is quiet.
There have been almost 1,000 Covid-19 cases reported in the country.
But polio, which can cause paralysis or even death, is also making a comeback - four new cases have been reported since February.
Zeinabou Tahirou sits in a pink headscarf and a blue face mask, cradling her baby girl, Fadila.
"I was so scared to come here, because of the coronavirus," she says.
"But health workers have told me how important these immunisations are, and also what I need to do to stay safe - like washing my hands all the time."
At least 80 million under the age of one are at risk
Estimated number of babies missing routine vaccinations because of the coronavirus pandemic:
- South East Asia - 34.8 million
- Africa - 22.9 million
Current outbreaks of preventable deadly diseases:
- Nepal and Cambodia - measles
- Ethiopia - measles, cholera and yellow fever
Source: The World Health Organization, Unicef, Sabin Vaccine Institute and Gavi, the Vaccine Alliance
Recent modelling by Johns Hopkins Bloomberg School of Public Health suggests disruption to these kinds of crucial health services for women and children, could result in as many as 6,000 additional children dying every day.
"What we fully expect is these diseases will come roaring back," WHO immunisation and vaccines department head Kate O'Brien says.
"And what that means... is that we're going to see deaths of children in numbers that are unprecedented in recent times."
But this potentially devastating situation can still be prevented, "if governments act now".
The warnings come as global leaders meet virtually for the Global Vaccine Summit, on Thursday, hosted this year by the UK.
Countries and donor organisations will be asked to pledge $7.4bn (£5.8bn) to ensure Gavi, the Vaccine Alliance can continue delivering lifesaving vaccines to some of the poorest communities in the world, both during the pandemic and beyond.
Its leader, Dr Seth Berkley, says ensuring routine vaccination systems are up and running again as soon as possible, is crucial.
"When you have a big effect on vaccine [services] like this, it takes some time to rebuild some of the systems around it," he says.
"As we rapidly move towards having Covid-19 vaccines available, these are the same systems we will use to deliver those vaccines as well."
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