Also Read: Older children spread the coronavirus just as much as adults, study finds But we don't have any data related seroprevalence study, where a sample of population is taken to see presence of the antibodies. Seroprevalance study helps to know about the percentage of people who have been infected with SARS-CoV-2.
Towards herd immunity Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. As a result, the whole community becomes protected. For herd immunity to kick in, a certain percentage of the population must be infected. That percentage is called a threshold proportion. For instance, measles has a threshold of 95 percent, which means that 95 percent of the population must be infected. But for other diseases like influenza it could be as low as 35 percent. The time taken to attain herd immunity threshold proportion depends on the effective reproduction number (R0) of the virus. Reproduction number refers to the transmission potential of a disease. Measles has an R0 of 12-18, which an infected person has potential to spread to 12-18 people, in the absence of preventive measures.For SAR-CoV-2, there are still studies going on but R0 is estimated at 2-6 percent, without interventions like lockdowns, social distancing, use of masks and personal hygiene. On threshold percentage, we still don't have a full picture but it is estimated between 29 and 80 percent.
If you take a minimum of 29-30 percent threshold, Iran may have reached the threshold of herd immunity. Even on the higher side as pointed out, it will be a matter of months for Iran to reach the herd immunity threshold.To be sure Sweden tried herd immunity but it backfired with a high proportion of deaths and the UK swung from herd immunity to lockdowns and other measures.Also Read: Exposure to SARS, other coronaviruses may make some people immune to COVID-19: Report
The problem is natural herd immunity is risky for vulnerable populations like aged and people with comorbidities, leading to overwhelming healthcare systems. And it was found out that getting to herd immunity is very slow into those countries. The build up of herd immunity differs from country to country. For instance India is more closer to Iran, than a European country.So what this possibly means is that Iran may not need a COVID-19 vaccine - generally considered as fastest and surest way to reach herd immunity. In a realistic scenario, the possibility of the vaccine reaching people, isn't going to be possible at least for the next six months. By that time Iran going by Rouhani numbers will reach almost 75 percent threshold.However, there are many unknowns about COVID-19 that could have bearing on herd immunity. We still don't know how long we have protection to COVID-19 or how long the antibodies produce will last. If the protection doesn't last beyond a season, then there will be a problem with the feasibility of natural herd immunity.
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