COVID Booster: loss of smell and social influence

Loss of smell is the best sign of COVID-19

More a confirmation: two international studies agree that the majority of patients with respiratory infections lose their sense of smell due to COVID-19. They were also found to lose taste and other senses in the mouth. 

More than 4,500 COVID-19 patients of 23 nationalities worldwide responded to the researchers’ questionnaire. 

Both studies are published in Chemical Senses. 

The two studies used answers from the same questionnaire, finding the average loss of smell was 79.7 on a 0–100 scale, which is indicative of a large to complete sensory loss. 

“This emphasises how important it is to be aware of this symptom, as it may be the only symptom of the disease,” says co-author Alexander Wieck Fjaeldstad, from Aarhus University, Denmark. He also stresses that only around half of the patients with a loss of smell have gotten it back after 40 days.

The collaborative work also found that the sense of taste was reduced, sitting at 69.0 on the 0–100 scale. 

“While the loss of smell in itself removes the ability to sense the aroma of food, the simultaneous loss of other senses makes it difficult to register what you’re eating,” Fjaeldstad says. “Putting food in your mouth can therefore become a decidedly unpleasant experience.”

Social influence shapes response to restrictions

People are more likely to follow COVID-19 restrictions based on what their friends do, rather than their own approval of the rules, according to a study published in the British Journal of Psychology.

2100122 social distancing
Credit: Alex Schwab

Research from the University of Nottingham, UK, found the most diligent followers of COVID guidelines were those whose friends and families also followed the rules. The discovery applied to all age groups, genders, countries and was independent of the severity of the pandemic and level of restrictions.

Lead researcher Bahar Tunçgenç says he was struck by how differently national leaders in Europe and Asia were responding to the pandemic.

“While the West emphasised ‘each person doing the right thing’, pandemic strategies in countries like Singapore, China and South Korea focussed on moving the collective together as a single unit,” he explains.

“There is much that human behaviour research can offer to implement effective policies for the COVID-19 challenges we will continue to face in the future. Our message to policymakers is that even when the challenge is to practise social distancing, social closeness is the solution!”

Mild vs severe cases: who has longer-lasting immunity? 

A new study suggests people with severe COVID-19 cases may be left with more of the protective “memory” T cells that are needed to fight reinfection.

A research team from La Jolla Institute for Immunology (LJI), US, and the universities of Liverpool and Southampton, UK, studied the expression of individual genes in more than 80,000 CD8+ T cells, isolated from both COVID-19 patients and individuals not exposed to the disease.

The CD8+ T cells are responsible for destroying virus-infected host cells. “Memory” CD8+ T cells are also crucial for protecting the body from reinfection against many viruses.

One would expect to see a stronger CD8+ T cell response in patients with milder cases, since the immune system was equipped to fight off the infection, but the study found the opposite.

They found weaker CD8+ T cell response in patients with milder COVID-19 cases compared to severely ill patients, who’d required hospitalisation or ICU support. 

“The data from this study suggest people with severe COVID-19 cases may have stronger long-term immunity,” says study co-leader Pandurangan Vijayanand, from LJI.

In fact, the researchers found molecular signs of a phenomenon called T cell “exhaustion”.

“People who have severe disease are likely to end up with a good number of memory cells. People with milder disease have memory cells, but they seem exhausted and dysfunctional – so they might not be effective for long enough,” says Vijayanand.

The work is published in the journal Science Immunology. 

COVID-19 virus triggers antibodies from previous coronavirus infections

Results from a new study suggest the immune systems of people infected with COVID-19 may rely on antibodies created during infections from earlier coronaviruses to fight off the disease. The work is published in the journal Cell Reports Medicine. 

Humans have navigated at least six other types of coronaviruses, such as MERS-CoV that caused the 2012 outbreak of Middle East Respiratory Syndrome, and SARS-CoV-1, that caused the 2003 outbreak in Asia of Severe Acute Respiratory Syndrome.

The researchers also analysed antibody responses of four older coronaviruses, which are called “common” coronaviruses and are endemic through human populations, although generally not deadly.

“Our results suggest that the COVID-19 virus may awaken an antibody response that existed in humans prior to our current pandemic, meaning that we might already have some degree of pre-existing immunity to this virus,” says senior author John Altin, from the Translational Genomics Research Institute (TGen), US.

By comparing the patterns of reactivity against the different coronaviruses, the researchers demonstrated that SARS-CoV-2 could summon antibodies that were originally generated in response to previous coronaviruses.

The researchers say their findings help explain the widely varying reactions COVID-19 patients have to the disease – from mild to no symptoms, to severe infections requiring hospitalisation and often resulting in death.

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