What does the recent seroprevalence study mean?Two-thirds population with antibodies to Covid-19 does not mean they are immune to future infections. Misinterpretation of study could lead to surge in cases.
On Monday, the Ministry of Health and Population released a statement that said a preliminary report of the nationwide seroprevalence study showed 68.6 percent of the country’s population has already developed antibodies to Covid-19.
Officials said that the detection of antibodies in a large number of people, both vaccinated and unvaccinated, should be taken positively. They also claimed that a large-scale outbreak of Covid-19 is unlikely in the immediate future.
Authorities in various districts, including in Kathmandu Valley, which is still a major coronavirus hotspot, have started dropping their guard–schools, cinemas and gyms are being reopened. Despite the high infection risk and the Kathmandu Valley still reporting a high number of cases–the Valley still has 9,000 active cases–authorities concerned seem indifferent to political rallies and religious and other events. Public health experts have warned that the preliminary results of the seroprevalence study, which is confusing and misleading, could increase complacency in all sectors and lead to a spike in new infections.
Here’s everything you need to know about the seroprevalence study.
What is a seroprevalence study?
Serology or antibody testing checks blood samples to look for antibodies to SARS-CoV-2, the virus that causes Covid-19. A seroprevalence survey is carried out in a larger population to estimate the percentage of the population with antibodies.
When and where was the study carried out?
Blood samples were collected from 76 districts (excluding Manang) on a random sampling basis between July 5 and August 14. The sample size was over 13,000. Those samples were tested at the National Public Health Laboratory in Teku. The study was carried out with the technical and financial assistance of the World Health Organisation.
The Health Ministry had carried out a similar study in 2020 but refrained from publishing the report. The previous study had shown that around 15 percent of the country’s population had developed antibodies to SARS-CoV-2, with some districts reporting up to 28 percent.
Does having Covid-19 antibodies mean a person is protected from future infections?
Doctors say no. According to experts, antibody tests or serology tests are carried out to check antibodies in blood samples to determine if a person has had a previous infection. A positive antibody result does not always guarantee that a person is protected against future infections.
Some of these antibodies have little influence on whether the body can defeat the infection. So even if a person had a past infection and a positive result, the antibody may not be the "rapid neutralising antibody" that blocks the SARS-CoV-2 virus from infiltrating cells and replicating.
Do antibody tests show that vaccines are working?
According to the Health Ministry’s report, 80 percent of the population who have taken the first dose of the vaccine and 90 percent of the fully-vaccinated population have developed antibodies against SARS-CoV-2.
But experts say that many Covid-19 antibody tests are not designed to specifically detect antibodies that develop due to vaccination and thus cannot show whether antibodies are of the right quantity or quality for protection against infection or illness.
Rapid antibody tests only show whether or not antibodies are present, without providing any quantitative information. In other words, just because someone has a positive antibody test does not automatically mean that their level of antibodies is high enough to protect against Covid-19 infection. Furthermore, antibodies vary in their ability to neutralise viruses–a property not measured by routine antibody tests.
Why does past Covid-19 infection not guarantee protection from future infections?
Doctors say a neutralising antibody test is required to know whether or not the antibodies present in the body work against new infections. The serology test conducted by the Health Ministry is not the neutralising antibody test.
A neutralising antibody is an antibody that is responsible for defending cells from the pathogen, 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.
Neutralising antibodies can sometimes be missing in the people already infected with the virus, which means they can be reinfected, which has been validated by cases of reinfection reported from across the country. The severity of cases and deaths prove that past infection doesn't guarantee protection against future infections. Additionally, variants of the SARS-CoV-2 keep mutating, and studies have shown that new variants of the virus could evade immunity developed from other variants.
Is it possible for people residing in all seven provinces, cities and villages, and all three geographic regions to develop similar levels of antibodies?
In its statement issued on Sunday, the Health Ministry said that similar levels of antibodies had been found in people residing in all seven provinces, all three geographical regions–mountain, hills and the Tarai, villages and towns, all genders, professions and groups.
In a regular press briefing on Wednesday, the Health Ministry gave a breakdown of the study results. According to Dr Krishna Prasad Paudel, the ministry spokesperson, 69.6 percent male and 67.4 percent female survey subjects have antibodies. Likewise, 72.4 percent of people residing in Tarai, 65 percent population living in the hills and 60 percent living in the mountains have Covid-19 antibodies. According to the study, 64.3 percent of the population who have not taken any vaccine also have antibodies.
Officials at the Health Ministry say that the recent decline in new cases could be because two-thirds of the population has already been infected with the virus, and that the risk of a massive explosion of new infections remains low.
Doctors, however, are sceptical of such claims, adding that it is impossible to develop antibodies proportionally as people in the highly affected areas would have more antibodies than those in the remote areas where cases of infection have not been detected or only a few cases have been confirmed.
The development of similar levels of antibodies in all age groups, another of the Health Ministry’s claims, is an unheard-of concept that has not been reported anywhere in the world. Studies show the development of the antibodies level varies according to age. According to the World Health Organisation, the 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 who developed severe illness. Some studies have also suggested that waning of antibody levels occurs within several months after infection in some individuals.
Do antibodies developed from vaccination last forever?
No. Studies show that even antibodies developed from vaccines wane over time. Several countries, including the United States of America, have decided to provide booster shots to those with compromised immunity.
Some studies also show that vaccines are effective against the Delta variant of the virus, but their protection decreases over time, weakening significantly within three months.
Is Nepal close to reaching herd immunity level?
Paudel, the spokesperson for the Health Ministry, asserts that time has not come yet to talk about herd immunity, as the levels of antibodies have not been checked by the study and how much protection the antibodies provide is still not known. Several international studies show that antibodies developed from both natural infection and vaccination wane over time, and antibodies developed from one variant of the virus may not work against another variant.
As the coronavirus keeps mutating, it may be impossible to reach the herd immunity level. People in Nepal are getting reinfected and those vaccinated are also getting infected, according to Paudel.
Moreover, only over 15 percent of the country’s population has been immunised fully as of now, which means around 85 percent of the population is yet to be fully vaccinated.
Why is understanding the correct meaning of 68.6% serology positive results important?
After the ministry statement on the seroprevalence study, some officials 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 the disease from person to person unlikely.
Sushil Koirala, a public health expert, says the misinterpretation of Covid-19 serology tests can lead to a false sense of protection and people could disregard proven prevention measures. He adds that the wrong conclusions about vaccine efficacy may influence others to refuse vaccination, ultimately amplifying the spread of disease.
What is Nepal’s vaccination status?
As of Thursday, 5,425,888 people (over 18 percent) have taken their first dose of the vaccine and 4,677,976 people (15.59 percent) have been fully immunised against Covid-19.
Nepal has administered over 10 million doses as of Thursday.
The country had earlier aimed to inoculate 21,756,763 people, or 72 percent of the population, above 14 years old against Covid-19, but the vaccine is being administered to people above the age of 18 only. The Health Ministry has said that it has signed a deal to purchase Moderna Covid-19 vaccine to inoculate all those above 12 years old.