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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.

When and how to use masks

When to use a mask

  • Before putting on a mask, clean hands with alcohol-based hand rub or soap and water.
  • Cover mouth and nose with mask and make sure there are no gaps between your face and the mask.
  • Avoid touching the mask while using it; if you do, clean your hands with alcohol-based hand rub or soap and water.
  • Replace the mask with a new one as soon as it is damp and do not re-use single-use masks.
  • To remove the mask: remove it from behind (do not touch the front of mask); discard immediately in a closed bin; clean hands with alcohol-based hand rub or soap and water.

How to wear medical masks

  • If you are healthy, you only need to wear a mask if you are taking care of a person with COVID-19.
  • Wear a mask if you are coughing or sneezing.
  • Masks are effective only when used in combination with frequent hand-cleaning with alcohol-based hand rub or soap and water.
  • If you wear a mask, then you must know how to use it and dispose of it properly.

Can a face mask protect me from coronavirus? Covid-19 myths busted

However, masks will probably make little difference if you're just walking around town or taking a bus so there is no need to bulk-buy a huge supply.

Wearing a face mask is certainly not an iron-clad guarantee that you won't get sick - viruses can also transmit through the eyes and tiny viral particles, known as aerosols, can penetrate masks. However, masks are effective at capturing droplets, which is a main transmission route of coronavirus, and some studies have estimated a roughly fivefold protection versus no barrier alone (although others have found lower levels of effectiveness).

If you are likely to be in close contact with someone infected, a mask cuts the chance of the disease being passed on. If you're showing symptoms of coronavirus, or have been diagnosed, wearing a mask can also protect others. So masks are crucial for health and social care workers looking after patients and are also recommended for family members who need to care for someone who is ill - ideally both the patient and carer should have a mask.

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