Covid-19 antibodies in large chunk of population may not mean immunityExperts say the hurried statement on seroprevalence study could create confusion, as it’s premature to conclude Nepal is close to reaching herd immunity.
Preliminary findings of a new nationwide seroprevalence study by the Ministry of Health and Population show that 68.6 percent of the country’s population has already developed antibodies against Covid-19.
The latest findings of the study, the detailed report of which is yet to be released, indicates that SARS-CoV-2 has spread rampantly in the communities and measures taken to break the chain of transmission are inadequate and ineffective as over two-thirds of the country’s population has already been infected before August 14.
Carrying out such a large-scale survey among the general population offers public health agencies a picture of the spread of infection in communities, especially during a pandemic that killed over 10,700 people.
But on Sunday, a statement by the Health Ministry outlining preliminary findings of antibodies and vaccine efficacy has given room for misinterpretations, according to public health experts who say it would be dangerous to make a hasty conclusion.
“We don’t know the percentage of the antibodies... or if it is effective against the Delta variant of the virus circulating in communities at present,” Dr Dipesh Tamrakar, an assistant professor at the Kathmandu University, who served under the Community Medicine Department at Dhulikhel Hospital, told the Post.
In its statement on Sunday, the Health Ministry also said that similar levels of antibodies had been found in people residing in all seven provinces, all three geographical areas–mountain, hills and the Tarai, villages and towns, all genders, professions and groups.
Officials at the Health Ministry say that the recent decline in new cases could be a reason for two-thirds of the population already infected with the virus and that the risk of a massive explosion of new infections remains low.
Doctors, however, say that it is impossible to develop a similar level of antibodies in the people residing in all seven provinces throughout the country and all three geographical areas, towns and villages and people of all ages.
“Development of similar levels of antibodies in all age groups has not happened anywhere in the world,” said Tamrakar. “Studies show it (development of the antibodies level) varies according to age, and it is a proven fact.”
Some countries, including the United States, have decided to give a third dose as a booster shot to those with compromised immunity.
“We also do not know whether or not the antibodies work against the new variant of the virus,” Dr Prabhat Adhikari, infectious disease and critical care expert, told the Post. “For that, a neutralising test is required, which we have not done yet.”
A neutralising antibody is an antibody that is responsible for defending cells from the pathogen, which are organisms that cause diseases. They are produced naturally by the body as part of its immune response, and their production is caused by both infection and vaccination against infections.
According to the World Health Organisation, available scientific data suggest that in most people, immune responses remain robust and protective against reinfection for at least six to eight months after infection (the longest follow up with strong scientific evidence is currently approximately eight months).
Individuals with mild or asymptomatic infection tend to have lower antibody levels than those with severe disease. Some studies have suggested that waning of antibody levels occurs within several months after infection in some individuals.
After the ministry statement on the seroprevalence study, some have been quick to say that the country is close to reaching herd immunity, a situation when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely.
“We are nowhere close to reaching a herd immunity level, as a huge number of the population is yet to be fully vaccinated,” Dr Sher Bahadur Pun, a virologist and chief of the Clinical Research Unit at Sukraraj Tropical and Infectious Disease Hospital, told the Post.
Going by the ministry statement, doctors say 10 percent of the fully vaccinated population and 20 percent of those who have taken the first dose do not have antibodies. This, according to them, means there is a chance of getting infected–severely–and even death.
Though vaccination is the best way to protect against the SARS-CoV-2 infection, some studies show the existing vaccines are less effective against the Delta variant, and discussions are being held to administer booster shots.
The Health Ministry said that the Delta variant of the virus is responsible for the ongoing infection throughout the country. Whole-genome studies carried out in the past also showed that the Delta variant of the virus, which is highly infectious, is circulating throughout the country.
“The study shows people in all three geographical areas and all seven provinces have similar levels of antibodies,” Dr Samir Kumar Adhikari, joint spokesperson for the Health Ministry, told the Post. “The study indicates a large number of people have antibodies which may mean we may not see a large-scale outbreak immediately.”
Adhikari, however, concedes that immunity developed by natural infections wanes after a certain period and public health measures are still relevant.
So far, 5,317,483 people have taken their first dose of the vaccine (17.7percent), and 4,396,402 (14.65 percent) have been fully vaccinated.
“As the coronavirus keeps mutating, immunity developed from one variant may not protect an individual against another deadly variant,” said Pun. “Risk has not lessened at all. Authorities concerned should still focus on preventive measures.”
The World Health Organisation’s chief scientist Dr Soumya Swaminathan recently said that Covid-19 in India may be entering some kind of endemic stage, where there is a low or moderate level of transmission.
Doctors say the situation will be different in Nepal if the virus enters the endemic stage in India.
On Monday, 1,902 people tested positive from 11,892 polymerase chain reaction tests, and an additional 393 people tested positive in 4,341 antigen tests.
The positivity rate is around 16 percent.
Doctors say the decline in tests could be the reason for the less number of new cases. Currently, thousands of healthy people going abroad are undergoing tests every day. The Health Ministry, in its daily report, also includes the test results of those people who seek tests for getting “negative reports” required for flying abroad for studies or work, thereby creating confusion about the actual Covid-19 situation.
“Infection rate has remained almost constant for months, and the positivity rate has hovered around 15 percent,” said Pun. “We don’t know the exact scale of the spread, but Covid-19 may become endemic in our country too.”