Amid the fears of a fourth Covid wave in India triggered by Omicron BF.7 that is currently wreaking havoc in China, a top official of CSIR- Centre for Cellular and Molecular Biology (CCMB) said that the severity of Omicron BF.7 in India may not be as serious as in China because Indians have already developed ‘herd immunity’. Meanwhile, central and state governments have been urging people to follow Covid-appropriate measures such as wearing masks, social distancing and also getting vaccinations. So far, four cases of Omicron BF.7 have been detected in India in total. (Also read: Omicron BF.7: Cases of highly infectious strain rise in India; experts on symptoms, precautions and fresh wave)
Herd immunity is a kind of protection that a population gets when it becomes immune to an infection, be it through previous infections or vaccination, and thus the likelihood of infection for individuals who lack immunity gets reduced. So can herd immunity lead to milder symptoms of Covid or protect us from fourth Covid wave? We asked experts.
WHAT IS HERD IMMUNITY
Dr Pavithra Venkatagopalan, Coronavirologist and Covid Awareness Specialist, Rotary Club of Madras NextGen tells HT Digital over a telephonic conversation how herd immunity works.
“Let us assume there are a hundred people in a room and there is one person called ‘A’ at one end and the other person called ‘B’ at the opposite end. A is infected and the target is to reach B. However, A can only reach B if it passed through all the other 97 people in the room or at least 50% of people in the middle. If halfway through there are people that don’t get the infection at that point the infection gets blocked, which means that person cannot transmit it. In the same way, the virus will keep trying through everybody, but it might not reach the other person as enough people in the group maybe stopping the transmission. When it happens such a way, more than 60% of the people are able to block the infection. Then you sort of develop herd immunity,” explains Dr Pavithra.
“Herd immunity is when a large portion of a population is having antibodies developed either naturally or through vaccines. Have antibody against certain infection provides herd immunity against that infection. In general, when herd immunity is high for a particular infection it helps in decreasing the active symptoms of the disease or also decrease the transmission of the infection, but when it comes to the Omicron variant BF.7 and other newer variants, what happens is that these variants actually have immune escape phenomena that they invade their existing immunity and as such there are chances that herd immunity might help in preventing severe infection because of pre-existing antibody. However, we will still get milder cases and the transmission and infectivity of virus,” Dr. Ankita Baidya, Consultant Infectious Disease, HCMCT Manipal Hospitals, Dwarka told HT Digital.
She says that right now with so many people vaccinated in our country so efficiently with first and second doses, it is possible that in urban pockets, we have achieved a significant amount of herd immunity.
CAN HERD IMMUNITY PROTECT US FROM OMICRON BF.7 WAVE?
The coronavirologist further explains how herd immunity can help in case of Omicron BF.7 wave.
“It is quite possible even if the Omicron BF.7 wave comes to get us, first of all the efficiency with which it is being transmitted to people would be less because enough people are vaccinated. Even if a vaccinated person gets the infection, they will have mild symptoms. They will spread it less efficiently than someone who’s unvaccinated because their body is already fighting it. It (herd immunity) can protect us from severe infection. So, if we have Omicron wave it can protect us,” says Dr Pavithra.
OMICRON WAVE WILL BE MILDER THAN DELTA WAVE
“Recently, as BF.7 subvariant of Omicron cases continue to cause havoc in China and further spreading to Japan, Brazil, Thailand and US (and now in India too), there are chances of a wave all around the world in next few months. But this wave is not expected to be as grave and serious (with mortality and severity) as compared to the Delta wave in 2021. The reason being that a large group was infected with Delta variant in 2021, after which a natural immunity existed with antibodies. At the same time, we started our vaccination drives which immunised a larger group. When Omicron hit us in 2022, we were getting booster doses. Hence, Indians have a protection from natural and passive immunisations as well. This will certainly help in decreasing hospitalizations, severity of infections and mortality in BF7 cases,” says Dr Charu Dutt Arora, Consultant Physician and Infectious Disease Specialist Head, Ameri Health, Asian Hospital, Faridabad.
DOES DEVELOPING HERD IMMUNITY MEANS MILDER COVID INFECTIONS?
Dr Pavithra says there is no way to predict we will continue to have mild infections. She says the virus can evolve in any direction; it can be extremely virulent or severe. “But these things can protect us and give us better outcome compared to if we were completely unvaccinated,” she says.
“Since it changes its genetic structure in the way to evade the immune response, in future also we will repeatedly see mild infections. Also, number of cases can go high when actually the immunity goes down against certain variant and a new variant is in circulation, we may see mass level of infection and outbreak with different variant of this viruses. Because of herd immunity we can see milder form of COVID in most of the patients who get this infection,” says Dr Baidya.
WHAT HAPPENS TO UNVACCINATED PEOPLE?
“Completely unvaccinated people or completely unexposed to virus people we don’t know how their symptoms will be. Depends also on their immune status. Some people might have mild infections for some people it can be severe. It is something we have to wait and watch for. We do not have population to test this on as people either have had Covid or vaccinated. Those who have been vaccinated are most likely to be better protected than those who have just been infected,” says Dr Pavithra.
‘UNVACCINATED PEOPLE ARE AT RISK OF BAD FORM OF COVID’
“This is a concern that people who are unvaccinated in phase of new subvariant the antibody in their blood is low and, in that case, they can have a bad form of Covid. So, it is important that the booster dose of the vaccine has to be taken,” says Dr Baidya.
“BF7 cases will continue to come, but the patients will show milder symptoms (such as cough, cold, fever, bodyache) and will not need hospitalizations or oxygen support. Only the unvaccinated group and ‘high risk population’ such as elderly, immuno compromised and children might have a higher chances of catching and spreading the infection. They need to be more vigilant about the symptoms and should seek medical attention urgently. It is for us to continue following covid appropriate behavior and get tested and treated if anybody shows any symptoms. This will be helpful in checking the spread of infection. Vaccination is the biggest tool we have to prevent the disease and decreasing the severity of illness worldwide,” says Dr Arora.
