"There is only a 10 to 20% chance of family members getting infected if one member has contracted COVID-19," said Dileep Mavalankar, Director of Indian Institute of Public Health, Gandhinagar.
Dileep Mavalankar discussed the global literature review published by Indian Institute of Public Health in an interview with DataBaaz. Titled 'Secondary Attack Rate of COVID-19 in Household Contacts: Systematic Review,' published in the Quarterly Journal of Medicine in Oxford, UK, it reviewed 13 papers published globally about household family transmission of COVID-19 (referred to as the secondary attack rate).
Research from around the world — countries like China, Korea, USA, UK, and Italy show that the secondary attack rate to be not more than 50%. "Most research papers from around the world have a low secondary attack rate. 80 to 90% members of a family do not get infected even when one member is infected," said Mavalankar.
This study is supported by an ICMR study that showed an average secondary attack rate to be between 6 to 8% in the Indian context.
This is also in a scenario in a household where one primary case is reported but there is no social distancing or wearing a mask, and most people are diagnosed positive after symptoms showing up after a few days.
"The virus spreads very fast, but everybody is not susceptible to the virus. Large number of people in our country are having resistance, either innate or acquired, to the virus," he added.
International research studies also highlight an interesting fact, that a few families have zero secondary infection and some have many secondary cases. Mavalankar interprets this as it being a function of viral load carried by the first person, the immunity of the other family members.
However, this phenomenon is not new stressed Mavalankar. After chikungunya came back in a mutated form after 40 years in 2006, not many were infected, even if mosquitoes that transmit the disease were ever present.
This can be even seen in diseases like tuberculosis. "Almost 40% of Indians are infected, but the number of people who develop the disease, there is interplay of people the bacteria of tuberculosis and one's own resistance body resistance," he said.
Another important reason for people not getting infected is a concept developed by British neuroscientist Karl Friston, called the 'immunological black hole.' His theory proposes that said that half of the population in Europe is not even suseptible to these diseases.
"Factors like geographical isolation, people might have immunity due to some other infection, called cross immunity, or having innate immunity might contribute to this. Some are susceptible but develop mild infection that cannot be transmitted to others," he added.
"We also see the virus seems to be getting weaker, it is hitting populations that have already developed immunity. We are seeing milder and milder cases compared to what we saw in March and April," concluded Mavalankar.
Highlights:
-80 to 90% members of a family do not get infected even when one member is infected with COVID-19.
-This is a common phenomenon, seen in other infectious diseases like tuberculosis and chikungunya.
-The COVID-19 cases prevalent now are milder than what was seen in March and April.
Catch the interview on Youtube or click on the link here.
