COVID-19 Booster: Asymptomatic carriers

1. Protective immunity against SARS-CoV-2 could last up to eight months

A new US study reveals nearly all COVID-19 survivors may have protective immunity against SARS-CoV-2 virus for months and even years after infection. 

The research, published in an online edition of Science, analysed blood samples from 188 COVID-19 patients and found that parts of the “adaptive” immune system, which learns to fight specific pathogens, can last for at least eight months after the onset of symptoms from the initial infection.

The researchers found that if a person encounters SARS-CoV-2, memory B cells – which are cells that remember the virus they previously faced – could re-activate and produce SARS-CoV-2 antibodies to fight reinfection. COVID-19 survivors also had an army of T cells ready to fight reinfection. 

The researchers caution that immunity varies dramatically from person to person. 

“It looks like people who have been infected are going to have some degree of protective immunity against reinfection,” says co-author Daniela Weiskopf, from La Jolla Institute for Immunology. “How much protection remains to be established.”

2. More than half of all COVID-19 could be spread by people without symptoms

Modelling out of the US shows that 59% of all transmission of COVID-19 came from people without symptoms. Broken down, the researchers report that 35% of people transmitted the virus before they developed symptoms, while 24% of transmitters didn’t develop any symptoms. 

Authors of the study, published in JAMA Network Open, say their findings suggest that the identification and isolation of people with COVID-19 symptoms will not control the spread of the virus. 

“In the absence of effective and widespread use of therapeutics or vaccines that can shorten or eliminate infectivity, successful control of SARS-CoV-2 cannot rely solely on identifying and isolating symptomatic cases,” the authors write. “Even if implemented effectively, this strategy would be insufficient.”

3. The virus likely lingered longer than reported in Wuhan

A team of researchers in China estimate that thousands of people in Wuhan were likely infected, but asymptomatic, between March and May 2020, after the infection was believed to be under control in China. This means the virus lingered there for longer than reported.

Researchers from Wuhan City University tested 63,107 healthy individuals in China for SARS-CoV-2 antibodies. 

The blood samples, which were collected between 6 March and 3 May 2020, revealed that 1.68% of people had positive SARS-CoV-2 antibodies. That percentage is significantly higher than other regions in China, where the number of people with positive antibodies averaged 0.38%.

“We conclude that…a large amount of asymptomatic carriers of SARS-CoV-2 existed after elimination of clinical cases of COVID-19 in Wuhan City,” the authors report in the journal PLOS Neglected Tropical Diseases.

The total IgG and IgM antibody positive rate of SARS-CoV-2 in Hubei Province and other provinces with sample size >300 persons in mainland China. Asymptomatic carriers of SARS-CoV-2 in Wuhan City, Hubei Province, and China. Credit: Duan S, et al. (2021) (CC-BY 2.0)

4. COVID-19 is hard on people living with dementia

The COVID-19 pandemic is posing unique risks to people with Alzheimer’s disease and dementia, according to a new study from the University of New South Wales (UNSW) in Sydney. 

They’re at high risk of infection because cognitive symptoms make it difficult for them to follow safeguarding procedures, and living arrangements in care homes also enable the spread of the virus. 

The study also highlights further evidence that the brain pathology of some people living with dementia may increase the risk of neurological complications from COVID-19, such as stroke, brain haemorrhage and memory loss. 

“This is possibly due to an increased permeability across the blood-brain barrier of these individuals, which increases inflammation in the central nervous system in response to the virus,” says study coordinator Katya Numbers, from UNSW’s Centre for Healthy Brain Ageing. “This process ultimately causes further neurodegeneration.”

The negative effects of measures taken to slow the spread of the virus also have a great impact on this population group.

“The strict limitations imposed on their social activities and engagement with each other appear to have direct impact on neuropsychiatric symptoms and behavioural complications – mostly in residents with dementia, but also in people without any cognitive impairment,” Numbers says. 

5. From bad to worse in the US

As the chaotic political situation continues in Washington DC, COVID-19 isn’t slowing on any accounts in the US. On Wednesday 6 January, the country claimed a record COVID-19 daily death toll of more than 3860.

Total COVID deaths in the US passed 350,000 on Sunday 3 January; John Hopkins University reported a total of 365,174 deaths late on Friday 8 January (AEDT), when Brazil had the second-highest total of deaths at 200,498. Australia has recorded 909 deaths.

The US state of Arizona is reporting the highest rate of new COVID-19 cases in the country, with one out of every 119 people testing positive in the past week. 

Bonus: Australian vaccine rollout brought forward

Australian Prime Minister Scott Morrison has announced that vaccinations will begin in mid-February – earlier than originally anticipated. Morrison said the first to be vaccinated would be people working with international arrivals and quarantine, frontline health workers, aged care and disability workers, and people living in aged care or with a disability.

Reaction from the expert scientific community has been mostly cautiously positive.

“It’s good news that the start of the rollout of safe and effective COVID-19 vaccines has been brought forward in Australia,” says Hassan Vally, an epidemiologist from La Trobe University. “We should be beginning the rollout as quickly as the approval process allows, as the sooner we get started on this the more quickly we will achieve the health outcomes we want and the more confident we can be in moving all aspects of our lives forward.”

“The priority populations outlined… make sense and can be readily justified from various ethical viewpoints,” says Sydney University bioethicist Diego Silva. “Moreover, it is in keeping with the list from other jurisdictions – for instance, provinces in Canada, within the United Kingdom and the United States – with the exception of prioritising those who work with international arrivals, which makes ethical sense given Australia’s situation.”

One of those with concerns is Flinders University vaccine specialist Nikolai Petrovsky, who is also the research director of Vaxine Pty Ltd, which is undertaking clinical trials of a COVID vaccine.

“Premature approval of COVID-19 vaccines by Australia could have major negative public health ramifications,” he says. “Current approvals in other jurisdictions are Emergency Use Authorisations (EUA) and it is not clear from this announcement whether what is proposed is an EUA that restricts vaccine use to very specific populations or whether a more general approval is proposed, and if so, on what grounds?”

But CSIRO health and biosecurity director Rob Grenfell seems satisfied that the relevant checks and balances are in place: “This is a great step towards controlling COVID-19 in Australia,” he says. “It’s important to note that while the logistics are being sped up, safety is remaining everyone’s top priority. We can be reassured by the approach that Australia’s independent Therapeutic Goods Administration is taking, as one of the most stringent regulatory agencies in the world.”

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