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WHO warns that few have developed antibodies to Covid-19

Herd immunity hopes dealt blow by report suggesting only 2% -3% of people have been infected

Only a tiny proportion of the global population - maybe as few as 2% or 3% - appear to have antibodies in the blood showing they have been infected with Covid-19, according to the World Health Organization, a finding that bodes ill for hopes that herd immunity will ease the exit from lockdown.

"Easing restrictions is not the end of the epidemic in any country," said WHO director-general Dr Tedros Adhanom Ghebreyesus at a media briefing in Geneva on Monday. "So-called lockdowns can help to take the heat out of a country's epidemic."

But serological testing to find out how large a proportion of the population have had infection and developed antibodies to it - which it is hoped will mean they have some level of immunity - suggest that the numbers are low.

"Early data suggests that a relatively small percentage of the expanded may have been infected," Tedros said. "Not more than 2% -3%."

Dr Maria Van Kerkhove, an American infectious diseases expert who is the WHO's technical lead on Covid-19, said they had thought the number of people infected would be higher, but she stressed it was still too early to be sure. "Initially, we see a lower proportion of people with antibodies than we were expecting," she said. "A lower number of people are infected."

Santa Clara county had 1,094 confirmed cases of Covid-19 at the time the study was carried out, but antibody tests suggest that between 48,000 and 81,000 people had been infected by early April, most of whom did not develop symptoms.

But even those high figures mean that within the whole population of the county, only 3% have been infected and have antibodies to the virus. A study in the Netherlands of 7,000 blood donors also found that just 3% had antibodies.

Van Kerkhove said they needed to look carefully at the way the studies were being carried out. "A number of studies we are aware of in pre-print have suggested that small proportions of the population [have antibodies]," she said. These were "in single digits, up to 14% in Germany and France". "It is really important to understand how the studies were done."

That would include asking how they found the people to test. Was it at random or were they blood donors, who tend to be healthy adults? They would also need to look at how well the blood tests were performed.

"We are working with a number of countries carrying out these serology studies," she added. The WHO-supported studies would use robust methods and the tests would be validated for accuracy.

The hope will be that people who have had Covid-19 will be able to resume their lives. But Van Kerkhove last week said that even if tests showed a person had antibodies, it did not prove that they were immune.

Will there be a second wave of coronavirus?

As countries ease lockdowns, the worry is that populations remain highly vulnerable

With more countries planning to loosen restrictions imposed due to coronavirus but the UK prime minister, Boris Johnson, and the German chancellor, Angela Merkel, concerned about the potential for a resurgence or second wave, here is what we know from the rest of the world about the risk of Covid-19 coming back.

Will there be a second wave ?

Epidemics of infectious diseases behave in different ways but the 1918 influenza pandemic that killed more than 50 million people is regarded as a key example of a pandemic that occurred in multiple waves, with the latter more severe than the first. It has been replicated - albeit more mildly - in subsequent flu pandemics.

Other flu pandemics - including in 1957 and 1968 - all had multiple waves. The 2009 H1N1 influenza A pandemic started in April and was followed, in the US and varied northern hemisphere, by a second wave in the autumn.

How and why multiple-wave outbreaks occur, and how subsequent waves of infection can be prevented, has become a staple of epidemiological modelling studies and pandemic preparation, which have looked at everything from social behaviour and health policy to vaccination and the buildup of community immunity, also known as herd immunity.

While second waves and secondary peaks within the period of a pandemic are technically different, the concern is essentially the same: the disease coming back in force.

Is there evidence of coronavirus coming back elsewhere?

This is being watched very carefully. Without a vaccine, and with no widespread immunity to the new disease, one alarm is being sounded by the experience of Singapore, which has seen a sudden resurgence in infections despite being lauded for its early handling of the outbreak.

Although Singapore instituted a strong contact tracing system for its general population, the disease re-emerged in cramped dormitory accommodation used by thousands of foreign workers with inadequate hygiene facilities and shared canteens.

With 1,426 new cases reported on Monday and nine dormitories - the biggest of which holds 24,000 men - declared isolation units, Singapore's experience, although very specific, has demonstrated the ability of the disease to come back strongly in places where people are in close proximity and its ability to exploit any weakness in public health regimes set up to counter it.

Healthcare workers ‘should be screened for Covid-19 every week’

UK cancer specialist says leaving potentially infectious staff in hospitals is unethical

Healthcare workers should be screened for Covid-19 every week to protect patients from asymptomatic infection, the head of the Francis Crick Institute's testing facility has said.

The call comes amid concerns that hospitals are becoming hotspots for disease transmission and evidence that a significant fraction of those infected show few or no symptoms.

"For all our fuss about social distancing we fairly ignoring one of the main routes of infection in front of our eyes," said Prof Charles Swanton, who is leading the testing effort at the institute in London. "That's almost untenable to argue you should haven't been screening and isolating healthcare workers."

The institute is next week launching a pilot to screen staff at University College hospital to identify asymptomatic Covid-19 cases, but the approach has not been explicitly endorsed by the government and there have been no indications that this is being considered as a national strategy.

The institute's testing lab has capacity to run 3,000 tests a day, so would be capable of running a screening operation for staff at UCH, if this approach were adopted.

A possible concern is that screening could lead to large numbers of doctors and nurses, who are otherwise well, being required to self-isolate. But the alternative - leaving asymptomatic, but potentially infectious staff on the wards - runs contrary to the principle of "do no harm", Swanton said.

They're too scared to go to hospital and you can understand why

Patients were very aware of the risk, he added, and were staying at home due to justified fears that they could contract the virus by attending hospitals or seeing GPs.

The situation appears to be causing fewer emergency calls from people who have suffered strokes or heart attacks, potentially fuelling the rise in non-coronavirus deaths seen in figures released this week. Those with other conditions may also be deterred from seeking medical help.

On Thursday the Guardian reported that London A&E chiefs were concerned that patients were staying away, saying in a meeting last week: "People don't want to go near hospital. As a result salvageable conditions are not being treated."

Swanton, who is also chief clinician at Cancer Research UK, said: "I'm concerned that cancer patients need to be able to have the confidence to come into wards. We're in this for another month at least, probably two or three. That's a very long time to have a delayed cancer diagnosis."

There is growing evidence that a significant proportion of people infected with Covid-19 show few or no symptoms and that up to half of transmission may take place before symptoms occur.

A study of people onboard the formerly quarantined Diamond Princess cruise ship, which was docked in Yokohama, Japan, found 328 of the 634 positive cases (52%) were asymptomatic at the time of testing, and other studies have found a range of 20-80% of people carrying the virus but showing no symptoms.

To identify such cases, healthcare workers had ideally to be screened weekly in high-risk areas, Swanton said.

Graham Cooke, professor of infectious diseases at Imperial College London, agreed that screening should be seriously considered as the testing capacity is increased this month.

"I do think we need to raise the conversation about large-scale testing in healthcare settings," Cooke said. "Now we've got good evidence that there's significant transmission in people who are pre-symptomatic. We've got concerns about transmission in hospitals and we've got much-improved capacity for testing. There are reasons to be cautious, but one of them is not to be afraid of what we might find."

- The Guardian -

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