UK study claims COVID-19 immunity may not last over three months; newness of disease causing a paucity of data
The study included about 65 confirmed patients of the novel coronavirus infection and 31 health care workers who showed antibodies against the virus.
The COVID-19 disease has affected more than 13 million people in the world, of which it has killed more than 570,000. However, more than 7.5 million have recovered from the disease as well.
Generally, if a person gets an infection once, their body generates antibodies against the pathogen. So, the next time the person is exposed to the same pathogen, their immune system remembers it and quickly eliminates it.
However, since COVID-19 is a new disease, experts don’t fully know how the human immune system reacts to it or if those who get the infection once are safe from reinfection.
A previous study of the SARS-CoV-2 virus had shown that antibodies against the virus don’t last for more than three months.
Now, yet another study done at the King’s College London, UK indicates that COVID-19 patients show a sharp reduction in neutralising antibodies within three months.
The study is not yet peer-reviewed and hasn't been published yet.
Since vaccines also work on the development of immune response against a pathogen (without you ever developing the disease), the reduced antibody prevalence raises a lot of questions about the efficiency of vaccines and the possible end of the pandemic.
Antibody titer in mild vs severe COVID-19
The study included about 65 confirmed patients of the novel coronavirus infection and 31 health care workers who showed antibodies against the virus. Over 77 percent of all volunteers were male and the group had an average age of 55.2 years. Multiple samples were taken from all the volunteers and they were tracked for about 94 days starting from the onset of symptoms to check the magnitude of neutralising antibodies against SARS-CoV-2 in their body. Neutralising antibodies are those that actually neutralise the virus. Binding antibodies or non-neutralising antibodies are those that only bind with the virus and don’t neutralise it.
Here is what was found:
- IgM and IgA antibodies decline after 20-30 days of symptom onset. IgM is the first antibody that forms at the time of the infection. However, it usually doesn’t last long and is quickly replaced by other types of antibodies, mainly IgG. IgA is the antibody that provides protection to the mucosal surfaces - the nose and mouth for example.
- IgG antibodies remained at peak in most of the individuals even after 90 days of follow up. However, it was not the same in patients with severe and mild disease.
- The number of neutralising antibodies peak at about 23 days after the onset of symptoms regardless of whether the person has a mild disease or severe and reduced about 2 to 23 fold in the next 18-65 days.
- Those with severe disease developed a much higher neutralising antibody titer than those with mild or asymptomatic infection.
- In those who developed only a small amount of neutralising antibodies, the titer was almost undetectable after 50 days of follow up. However, those that had higher antibody titer, did show detectable antibodies even after 60 days and till the final day of the follow-up.
- The healthcare worker group had lower antibody levels than the patients even at the same disease severity scale. However, some asymptomatic workers did generate a high antibody response.
Things to consider
The authors of the study pointed out the following things that still need to be known:
- It is not known whether the high antibody titer in severe patients was responsible for disease severity or was it indicating a higher viral load.
- It is still not known if the IgG antibodies would reach a steady state after the follow-up period or if it would continue to decline. Previous studies with cold-causing coronaviruses have suggested waning of antibodies six months post-infection and undetectable antibody levels after four years.
- It is not known how much of an antibody level we need to be safe from reinfection with COVID-19 causing virus.
It is also worth considering that robust T-cell immunity has been found in recovered COVID-19 patients even in the absence of antibodies. Though it is not known whether T-cells can protect against SARS-CoV-2 reinfection, scientists have found them to be effective against reinfection by MERS (Middle East Respiratory Syndrome) virus.
For more information, read our article on Immunity to COVID-19.
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