Challenges in achieving herd immunity through vaccination

On December 1, Health Minister Rajesh Bhushan said the government had never spoken about national vaccination against COVID-19. In addition, ICMR Executive Director Balram Bhargava said, “If we can vaccinate so many people and stop the virus infection, we may not need to vaccinate the entire population. Maybe. “

However, the government’s idea of ​​vaccination of “critical masses” to break the chain of viral infections presents many challenges. Unlike Pfizer and Moderna mRNA vaccines, an interim analysis of Phase 3 trials of the Oxford vaccine is expected to prevent viral infections. However, the main purpose of the Phase 3 trial was to test its ability to prevent serious illness. Governments can break the transmission chain through vaccination only when a final analysis of Phase 3 data for the Oxford vaccine and other vaccines under development is available.

On the issue of the government avoiding universal vaccination, Dr. Anantvan, a global health and bioethics researcher, said in an email: “A clear announcement of the plan is needed. If you are vaccinated against a subset of the population, you need to see the scientific basis for that choice and how the decision to choose the subset was made.”

“In the case of an illness that affects everyone equally, everyone should be able to get vaccinated when the vaccine is ready. That the vaccine is a tool to promote health fairness. It’s important to remember, “said Dr. Gagandeep Kang, a professor of microbiology at CMC Velore, in an email. “If the goal is to achieve herd immunity, it should cover about 70% of the population. Unlike other infectious diseases that can identify groups at high risk of infection, SARS-CoV-2 The work is complicated. ”

Non-uniform transmission

For example, the level of vaccination required for herd immunity is determined by how the virus spreads within the population and is assumed to be uniform. However, the spread of the SARS-CoV-2 virus presents a high level of heterogeneous infection. This is why so many super-spreading events have occurred, with some infected people transmitting the virus to so many people and most infected people not transmitting the virus in small numbers or at all.

Targeted vaccination of sex workers and injectable drug users with more HIV cases helps prevent the virus from spreading to the general population, but in the case of coronavirus, such cases are concentrated. Absent. “Unlike HIV, there is no such group in SARS-CoV-2. Currently, even healthcare professionals using PPE have very low levels of infection, so many countries do not prioritize them. I’m thinking about that, “says Dr. Kang.

70% herd immunity to break the chain, especially given that two doses of the vaccine are required for complete protection and increased vaccine hesitation, especially as vaccine development and testing appear to be in a hurry. Is difficult to achieve. According to Dr. Kang, India covered 90% of all vaccines given during infancy only in January this year. If the vaccination program reduces the vaccination rate for children over the first year of life, it will be especially difficult with SARS-CoV-2.

High goal

“The COVID-19 vaccine also needs to reach an age group that is not currently targeted as part of large-scale vaccination. This is a design, logistics, and implementation challenge. National COVID -19 It is important to consider all these aspects when considering a vaccination plan, “says Dr. Bhan. Dr. Kang adds: “So if anyone asks me, I think I’ll set a high goal from the beginning, even if the coverage is gradual.”

Clinical trials test the effectiveness of the vaccine, but the actual effectiveness of the vaccine is only known if a large number of people have been vaccinated after the license. Also, the frequency of vaccination remains unknown because the duration of protection is unknown. She says it is very important to understand these and prevent resources from being diverted from existing vaccination programs that need to be continued.

Ethical issues

Given that the government has already listed high-priority groups for vaccination, the question of choosing other sections of the population that need vaccination to achieve herd immunity is ethically difficult. .. “An objective and transparent process for making prioritization decisions is critical to maintaining confidence in vaccination plans. These are publicly communicated, including the rationale for choice. It should be and there must be an appeal mechanism. Public input is very important, “says Dr. Bhan.

By the way, the purpose of identifying the first priority group to be vaccinated was to protect the group from severe illness and not to disrupt the route of transmission of the virus. “Breaking the chain of infection with partial vaccination of the population is not a concept I understand. Very high levels of coverage or appropriate levels of vaccination to control infection. And one of a well-performed combination of testing and isolation is required, “commented Dr. Kang. “I thought the purpose of prioritization was to first protect those at risk for serious illness and then move to lower-risk groups.”

Evidence update

Another controversial area is the issue of vaccination of people who are already infected. “The immunity provided by natural infections is probably long-term. Until date, we are not aware of the additional benefits or risks of vaccination of people who are already infected. It’s time to start some simple trials to update the evidence on the basis, “said Dr. Gilidarabab, an epidemiologist at the Indian Public Health Foundation in Bangalore.

Dr. Bab quoted the results of the Oxford vaccine trial, which showed 90% efficacy in patients receiving a half-dose, full-dose regimen, with low virus doses, good immune response, or both. Feeling mild or asymptomatic due to vaccination responds better.