Is Pakistan heading towards Covid-19 ‘herd immunity’?

KARACHI: Around 40 percent of Karachi’s population had already been exposed to coronavirus infection by the third week of July 2020 and by the first week of September 2020, at least 65-70 percent of the city’s population would be carrying Covid-19 antibodies, which means that Pakistan is rapidly heading towards achieving herd-immunity in around one and a half months, leading Pakistani health expert Prof. Dr. Tahir Sultan Shamsi claimed on Tuesday.

Dramatic decline in Covid-19 positive cases, reduced hospitalization cases and decreasing number of deaths as well as Anti-SARS-COV-2 antibody tests done on around 2,200-2,300 people from three different segments of the society in Karachi since April 2020 indicate that around 40 percent of the city’s population has developed Covid-19 antibodies so far, Prof. Dr. Tahir Shamsi told The News. “Our research on three different segments of the society reveals that around 40 percent of Karachiites have so far been infected with the coronavirus asymptomatically and by the first week of September 2020, 65-70 percent of city’s population would have been infected with the virus, which is a minimum requirement for achieving herd immunity in Covid-19 case," Dr. Shamsi, who is a prominent hematologist and health expert, further claimed.

Citing the example of Indian capital New Delhi,where officially only less than 1 percent of population has been tested positive, Dr. Shamsi said a population-based survey conducted by the Indian government has revealed that one in four persons in Delhi has already been exposed to coronavirus infection.

“In Karachi, based on antibody tests conducted by us at the National Institute of Blood Diseases (NIBD), Karachi, through five different FDA-approved kits and methods indicate that around 40 percent of the city’s population has already contracted coronavirus infection asymptomatically,” Dr. Shamsi claimed.

“We expect that by the first week of September 2020, around 65-70 percent population in Karachi would be carrying Covid-19 antibodies, which is required for herd immunity in a population,” Prof. Tahir Shamsi added.

Dr. Shamsi made it clear their results have some limitations it is “not a population-based study”, which has been conducted only at a centre in Karachi but added that results from three different segments of the society, including industrial workers, healthy blood donors and healthcare workers, indicate that around 40 percent of the city’s population has already contracted the disease without knowing about it, which is also evident from the declining number of Covid-19 cases in July so far.

“In April, only 5 percent people tested had developed Covid-19 antibodies, in May it reached 12pc and in June 21pc people from three different segments of the society were seropositive. The ratio is around 40 percent in the third week of July 2020," Prof. Shamsi said adding that Anti-SARS-CoV-2 antibody tests were done on Roche Kits on workers of media houses, industry, healthcare workers and healthy blood donors.

“Sample size was 700-800 in the each group respectively. We used the first generation kits and tested these people through five different FDA approved methods. Our results indicated that chances of false positive were very low as compared to false negative results," Dr. Shamsi added.

“We did the maximum work on Covid-19 antibodies in the last four months, from qualitative testing to quantitative analysis of Covid antibodies. No other institution has done any comparative work. Because of our major research on convalescent plasma, we had to do all the specialized tests," he added.

Stopping short of using the term “herd immunity” or saying Pakistan would definitely achieve immunity in the coming months, Prof. Tahir Shamsi claimed that by the first week of September, around 65-70 percent of Karachi’s population would be seropositive for Covid-19, which means that they would be carrying Covid-19 antibodies after contracting the coronavirus infection asymptomatically.

“For Covid-19, it is believed that if 70 percent of a city or country’s population is seropositive after contracting the disease or through vaccination, they would have had the herd immunity. The percentage of measles is 94 percent. I believe that we are heading towards achieving herd immunity, which is evident from declining Covid-19 positive cases and reduction in hospitalization through the country," Dr. Shamsi added.

Calling for a population-based sero-surveillance study in Pakistan, Dr. Shamsi said only a comprehensive sero-survey could help in ascertaining the actual percentage of people infected with Covid-19 in the country but added that he is surprised as neither the federal nor the provincial authorities are serious in launching a population-based study to know the actual spread of Covid-19 in the country.

“All parameters in Pakistan are indicating that we are heading towards herd immunity, which is evident from dramatic decrease in Covid-19 cases in the last 8-10 days," Prof. Shamsi said.

Terming Dr. Tahir Shamsi’s claims as “significant overestimation”, Pakistan’s leading epidemiologist Dr. Rana Muhammad Safdar said low prevalence increase false positivity of any screening test. “I am not very confident if the newly-used tests correctly detect Covid-19 antibodies or cross react with other preexisting ones as well," he added.

To a query, whether the National Health Services Academy has started a WHO-supported sero-surveillance in a sample of 6,000 population, he said the survey has not started yet.

Another leading infectious disease expert and PM’s focal person on Covid-19, Dr. Faisal Sultan said Dr. Tahir Shamsi’s claim is based on “single-source data”, which may be OK but one should be careful with extrapolations. “As far as my guess is concerned maybe 15 to 20. But let the serosurvey come in and we will know the accurate percentage of people who have contracted the disease in Pakistan," he said adding that there is an international collaboration for nation-wide serosurvey in Pakistan. “Despite its limitations, it needs to be done. Main issue is interpretation with knowledge,” he added.