Immunity to COVID-19 may only last for a matter of months, increasing the chances of a potential vaccine having to be administered more than once a year.
A large-scale Real-Time Assessment of community Transmission (REACT) study conducted by Imperial College London in UK, which involved 365,000 people found that antibody levels dropped by a quarter in three months.
Researchers states that this decline in immunity among population will result in an increased risk of reinfection of the virus.
Antibodies are a protein produced by the immune system which is released to inactivate foreign invaders, so they are a crucial line of defense against viruses.
Professor Helen Ward, one of the lead authors of the report stated that “the study has shown that the proportion of people with detectable antibodies is falling over time. We don’t yet know whether this will leave these people at risk of reinfection with the virus that causes COVID-19.”
The researchers further stressed that those who have already confirmed COVID-19 infection once should be more cautious in protecting themselves from catching it again.
“Testing positive for antibodies does not mean you are immune to COVID-19. It remains unclear what level of immunity antibodies provide or for how long this immunity lasts,” states Professor Paul Elliott, director of the program at Imperial College London.
The REACT study was conducted using finger-prick testing to detect coronavirus antibodies in the blood of more than 365,000 people. The tests were carried out in randomly-selected adult volunteers across the country at their homes.
The report, which was based on the findings of three rounds of testing carried out over three months shows that there were 17,576 positive results across all three rounds, out of which 30 percent did not show any COVID-19 symptoms.
The study also found that antibody prevalence decreased from 6 percent to 4.8 percent and then to 4.4 percent during the three months.
This drop was found among all age groups but the smallest drop was seen in the youngest age group, aged 18 to 24, whereas the largest decline was seen in the oldest age group which is 75 years and above.
However, a decrease in antibodies was not visible in healthcare workers. The researchers suggested that it may be because they have received repeated or higher initial exposure to the virus, scaling up a stronger immune response.
Studies have shown that asymptomatic infections of COVID-19 tend to produce low and in some cases, even undetectable antibodies, while those who suffer more symptoms shows a stronger immune response.
The findings build on a previous research which also found a decline in antibodies. A study by the University of Montreal found that antibody levels in the blood “drop rapidly” after infection.
Of the four reinfections cases studied by researchers, symptoms were worse in two patients, suggesting no clear pattern. Experts have said if SARS-Cov-2, which causes COVID-19, follows the same pattern as other coronaviruses, reinfections will become common.
In a study from Kenya in 2018, almost 30 percent of those who caught one variant of a coronavirus experienced a second reinfection. Around 10 percent caught it a third time and one person was infected four times.
Several reinfections occurred only three months after the first turn and in multiple cases the viral load increased, revealing ineffective protective immune responses after the initial exposure.