- A study from China compared the antibodies of 37 asymptomatic patients with another group of symptomatic patients with Covid-19
- It took much longer on average for the virus to clear from those with no symptoms
- Asymptomatic people also had far fewer antibodies – and a high proportion of those who recover lose their antibodies completely only a few months after infection
The idea of herd immunity has been touted by many in the midst of the coronavirus pandemic.
The idea is that when people get sick and recover, they develop an immunity that eventually gives the virus no foothold to stick around in communities.
But a new study from China, published in Nature, found strong evidence that suggests that some patients who recover from Covid-19 – including those with no symptoms – retain their antibodies against the disease for only between two and three months.
Antibodies against other types of coronaviruses normally last around a year.
READ: Top WHO official backtracks on comments that asymptomatic spread of Covid-19 virus is 'rare'
More research needed
Initially, the study focused on asymptomatic people that tested positive for the virus and to see what effect it had on their immunity compared to symptomatic patients.
The study involved 37 asymptomatic people who were isolated and hospitalised, and compared them to the same number of symptomatic people and those who tested negative with similar age, comorbidities and gender.
The average age of participants was 42 and the majority were women.
They found that the asymptomatic group on average had the disease in their system for 19 days, while for one individual in the group it was 45 days.
The symptomatic group’s average was 14 days – but the researchers noted that the viral load and its infective rate are not the same and that more research should be done on this.
Earlier this month, top WHO officials had to backtrack on comments that asymptomatic spread of the coronavirus was “very rare", stating that there hasn't yet been enough research done on this. According to their estimates, there could be anything between 6% and 41% asymptomatic cases in the population.
In the region where this study was conducted, the asymptomatic cases made up about 20% of confirmed cases at the time.
READ: Covid-19 antibody tests: Will they be reliable enough to manage the pandemic in the future?
Antibodies count low
But most importantly, this study shows that asymptomatic patients had a weaker immune response to the viral infection.
In the acute phase, their antibody count was much lower than in those who had mild symptoms, and during recovery about eight weeks after being discharged, 40% of the asymptomatic patients had no detectable antibodies while only 12.9% of the symptomatic group had the same result.
However, their results also showed that the asymptomatic individuals had a reduced inflammatory response characterised by low circulating concentrations of cytokines and chemokines.
The researchers concluded that the use of "immunity certificates" was thus not a useful tool to help communities manage the pandemic, and that isolation regulations from governments should continue to stay in place.
This also means that the maths on infection rates could be way off and more research is needed for an accurate prediction.
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