Herd immunity has been one of the key topics amid the coronavirus pandemic. Previous reports show that when a large proportion of the population gets immune to the novel coronavirus, through vaccination, herd immunity can be achieved.
A study in Spain, however, casts doubt on the prospect of herd immunity as a way to combat the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes the coronavirus disease (COVID-19).
What is herd immunity?
Herd immunity or community immunity happens when a high percentage of the community becomes immune to disease through vaccination or becoming infected with the virus. As a result, it makes the spread of the disease from person to person unlikely, providing people who are not vaccinated, such as newborns and those who are immunocompromised, some form of protection against the pathogen.
Vaccines help prevent many deadly and dangerous diseases. In some countries, for example, like the United States, polio and smallpox have been eradicated due to vaccination. However, some people may not be administered vaccines since they might pose a health threat, such as pregnant women, newborn babies, and those who have weak immune systems.
When many people, about 70 to 90 percent of the population, receive the vaccine or become immune to the virus, they help protect those who cannot receive the vaccine. This is termed as herd immunity.
Spain is one of the hardest-hit countries by the COVID-19 in Europe, and serological surveys have been essential tools to determine the magnitude of the outbreak. Since there are many asymptomatic carriers and limited access to diagnostic tests, serological surveys or antibody testing can help provide a picture of the extent of the COVID-19 spread in the country.
“By contrast, a population-based seroepidemiological survey can quantify the proportion of the population that has antibodies against SARS-CoV-2. A seroepidemiological study provides information on the proportion of the population exposed and, if the antibodies are a marker of total or partial immunity, the proportion of the population that remains susceptible to the virus,” the team explained.
The researchers conducted a nationwide antibody study, spanning more than 60,000 people, which showed that some 5.2 percent of the population in Spain had been exposed to the new coronavirus.
The results of the study, which was published in The Lancet, show that with the high infection toll in the country, these account for just a part of the whole population. To achieve herd immunity, at least 70 to 90 percent of a population needs to be immune to protect the uninfected.
This means that herd immunity is infeasible and unattainable since 95 percent of the population in Spain remains susceptible to the virus.
“The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas. Most PCR-confirmed cases have detectable antibodies, but a substantial proportion of people with symptoms compatible with COVID-19 did not have a PCR test and at least a third of infections determined by serology were asymptomatic,” the researchers said.
“These results emphasize the need for maintaining public health measures to avoid a new epidemic wave,” they concluded.
Latest Spain infection toll
Spain has reported more than 252,000 confirmed cases and more than 28,000 deaths. However, daily fatalities have gradually fallen since the end of April.
The country has started to ease its lockdown restrictions, but in the northwestern region of Galicia, officials re-imposed restrictions after an outbreak in the area. The local outbreaks were tied to the opening of bars, even if their capacity has been limited to 50 percent.
Worldwide, the global toll has topped 11.79 million, just days after the toll reached 10 million. The vast spread of the pandemic has spanned 188 countries and territories, with the United States reporting the highest number of confirmed cases of 2.99 million. The death toll in the country has exceeded 131,000.
The other countries that have reported high infection rates include Brazil, with 1.66 million cases, India, with more than 719,000 cases, Russia, with more than 693,000 cases, and Peru, with more than 309,000 cases.