World Health Organisation (WHO) has warned that it is too soon to know how long any immunity developed against COVID-19 might last. The appraisal comes as WHO leader Tedros Adhanom Ghebreyesus says COVID-19 is “10 times deadlier than the 2009 flu pandemic.”
“We know that in some countries, cases are doubling every three to four days,” Tedros said at a news briefing in Geneva on April 13. “However, while COVID-19 accelerates very fast, it decelerates much more slowly. ”
The 2009 H1N1 flu pandemic that Tedros referenced is estimated to have infected more than 60 million people in the U.S., according to the Centers for Disease Control and Prevention. The agency estimates the virus killed nearly 12,500 Americans in the span of one year. Nearly twice that number have already died from COVID-19 in the U.S., where some 570,000 people are confirmed to be infected.
More than 440,000 people worldwide are known to have recovered from COVID-19 — and their status is an important and lingering question. If people are immune after recovery, the thinking goes, they could resume normal life activities more quickly and provide both an economic boost and help in rendering essential services.
But for now, the answer to the question of whether people who have recovered can then be re-infected remains “an unknown,” Dr. Mike Ryan, executive director of WHO’s emergencies programs, said.
As far as developing immunity is concerned, there is only mixed information. According to Dr. Maria Van Kerkhove, an emerging disease expert who is the WHO’s technical lead on COVID-19, preliminary study on antibodies in the blood plasma of 175 patients, offers hope, but it has not been peer-reviewed.
The study “found some individual had strong antibody response,” Van Herkhove said, adding, “Whether that antibody response actually means immunity is a separate question.”
“There are many reasons why we might see reactivation of infection either with the same infection or another infectious agent,” he said. In general, “there are many situations in viral infection where someone doesn’t clear the virus entirely from their system.” Some patients can also clear the main infection but develop a secondary bacterial infection, he said.
The U.S. Centers for Disease Control and Prevention has said that it is developing a test to detect the presence of coronavirus antibodies to determine if a person could be immune to the disease. While such a test can determine who has been exposed to the virus, it’s not clear if it can identify those immune to reinfection, according to the WHO.
“While Covid-19 accelerates very fast, it decelerates much more slowly. In other words, the way down is much slower than the way up,” WHO Director-General Tedros Adhanom Ghebreyesus said at a press conference at the organization’s Geneva headquarters on Monday. “That means control measures must be lifted slowly and with control. It cannot happen all at once.”
Tedros outlined a checklist for countries before they should consider lifting social distancing measures:
- Transmission of the virus should be controlled.
- A surveillance system should be in place to detect, isolate and treat patients.
- Outbreaks in hospitals and nursing homes should be minimized.
- Preventive measures in essential locations such as schools and workplaces should be in place.
- The risk of importing the disease from abroad should be under control.
