Pakistan has registered another surge in its everyday tally of coronavirus infections during the last 24 hours (Tuesday) as the country reported 805 cases and one death, said the statistics released by the National Institute of Health Pakistan on Wednesday morning.

As per the NIH data, the death toll in Pakistan now crawled up to 30,405 after another fatality whereas the number of total infections now stood at 1,540,080 after adding the fresh 805 cases.

During the last 24 hours (Tuesday), 17,150 tests were conducted throughout Pakistan whereas the positivity ratio shot up to 4.69 percent. The number of patients in critical care was recorded at 168.

Fresh Covid outbreaks put millions under lockdown in China

Tens of millions of people were under lockdown in China on Wednesday as businesses in a major tourist city were forced to shut their doors and fresh clusters sparked fears of a return to blanket restrictions.

Health authorities reported over 300 infections Wednesday, with clusters found in the historic northern city of Xi'an -- home to the Terracotta Army -- as well as the country's biggest city Shanghai.

The fresh cases and the official response to them have deepened fears that China may be set to return to the kinds of strict restrictions seen earlier this year, when Beijing's hardline zero-Covid policy saw tens of millions locked down for weeks on end. 

In Shanghai, some residents on social media Tuesday reported receiving government food rations -- a throwback to the month's long confinement in the spring.

"Let me tell you a scary story, Putuo district is sending out vegetables again," read one resident's viral WeChat post. 

"I'm so nervous, the epidemic has destroyed my youth. I'm about to go crazy," posted another Shanghai-based Weibo user.

Officials launched a new round of mass testing in over half of the city's districts after a rebound in cases since the weekend, closing all karaoke bars Wednesday after some infections were linked to six such venues.

And Xi'an -- a historic city of 13 million that endured a month-long lockdown at the end of last year -- was placed back under "temporary control measures" after 29 infections were found, mostly among waste recycling workers, since Saturday.

Public entertainment venues including pubs, internet cafes and karaoke bars would shut their doors from midnight on Wednesday, the city government said in a notice.

State media showed images of Xi'an residents queueing up for tests past midnight Tuesday, while stressing the city was not in lockdown.

Officials have blamed the city's outbreak on the BA.5.2 sublineage of the Omicron variant, which is more transmissible and immune evasive.

"The positive infections are all the BA.5.2 branch of the Omicron variant, and epidemiological tracing work is still in full swing," Xi'an health official Ma Chaofeng said at a briefing.

The fresh outbreaks pose a renewed challenge to President Xi Jinping, who last week reaffirmed his commitment to zero Covid despite the mounting economic cost.

Japanese bank Nomura has estimated that at least 114.8 million people are under full or partial lockdowns nationwide as of Monday, a sharp jump from last week's 66.7 million.

More than 1,000 infections have been reported since last week in central Anhui province, with dozens spilling over to Jiangsu province neighbouring Shanghai, threatening the core Yangtze Delta manufacturing region.

New US study helps de-mystify Covid brain fog

A small new study published Tuesday by scientists at the US National Institutes of Health suggests that the immune response triggered by coronavirus infections damages the brain's blood vessels and could be responsible for long Covid symptoms.

The paper, published in the journal Brain, was based on brain autopsies from nine people who died suddenly after contracting the virus.

Rather than detecting evidence of Covid in the brain, the team found it was the people's own antibodies that attacked the cells lining the brain's blood vessels, causing inflammation and damage. 

This discovery could explain why some people have lingering effects from infection including headache, fatigue, loss of taste and smell, and inability to sleep as well as "brain fog" -- and may also help devise new treatments for long Covid.  

NIH scientist Avindra Nath, the paper's senior author, said in a statement: "Patients often develop neurological complications with COVID-19, but the underlying pathophysiological process is not well understood."

"We had previously shown blood vessel damage and inflammation in patients' brains at autopsy, but we didn't understand the cause of the damage. I think in this paper we've gained important insight into the cascade of events."

The nine individuals, aged 24 to 73, were selected from the team's prior study because they showed evidence of blood vessel damage in their brains based on scans. 

Their brains were compared to those from 10 controls, with the team examining neuroinflammation and immune responses using a technique called immunohistochemistry.

The scientists discovered that antibodies produced against Covid-19 mistakenly targeted cells that form the "blood-brain barrier" -- a structure designed to keep harmful invaders out of the brain while allowing necessary substances to pass. 

Damage to these cells can cause leakage of proteins, bleeding and clots, which elevates the risk of stroke.

The leaks also trigger immune cells called macrophages to rush to the site to repair damage, causing inflammation.

The team found that normal cellular processes in the areas targeted by the attack were severely disrupted, which had implications for things such as their ability to de-toxify and to regulate metabolism.

The findings offer clues about the biology at play in patients with long-term neurological symptoms, and can inform new treatments -- for example, a drug that targets the build-up of antibodies on the blood-brain barrier.

"It is quite possible that this same immune response persists in Long COVID patients resulting in neuronal injury," said Nath.

This would mean that a drug that dials down that immune response could help those patients, he added. "So these findings have very important therapeutic implications."

With inputs from AFP.