Dr.Krishna Reddy Nallamalla, Country Director, ACCESS Health India.
The world is eagerly awaiting a vaccine against Covid-19. Announcements from lead runners have been encouraging. And yet, unanswered questions remain. These will be known only after full results are published in peer reviewed scientific journals. Moreover, the challenge of administering the vaccine to billions of people across the world is daunting. Each country will have to plan well in advance to finance, procure, and organize population-wide vaccination.
The challenge for India, with a population of over 1.3 billion, is huge. India has, in the past, demonstrated its abilities in meeting challenges of this nature, despite its weak health system. India boasts of one of the largest vaccine manufacturing capacities in the world. India boasts of a widespread network of frontline health workers (ASHA, ANMs, and Anganwadi workers among others) that has been effective in undertaking programs at scale.
A majority of Indian states are witnessing a declining caseload, despite greater unlocking of restrictions. Multiple seroprevalence studies are pointing to a high rate of asymptomatic infections. Studies in a few slum communities have demonstrated very high seroprevalence rate ranging from 30 to 50 percent. These trends point to the phenomenon of natural herd immunity in the setting of continuing preventive measures of using face masks and practicing social distancing and hand hygiene.
The proportion of people required to be evidently immune in order to achieve herd immunity is arrived at by the formula (1-1/R0), where R0 is the reproduction rate of the virus, i.e., number of people one infected person infects. When the desired proportion of the population acquires immunity, the virus fails to spread in the population. It is well established that simple containment measures like face masking, social distancing, and hand hygiene can bring down the R0 value to <1.5 from a high of ~2.5 when no measures are in place. As per the above formula, the proportion of people needed to achieve herd immunity at R0 value of 2.5, 2.0, 1.5, and 1.2 are 60%, 50%, 33.3%, and 16.6% respectively.
Hence, the current decline in numbers should not give rise to a false sense of herd immunity and lead to lowering the guard in terms of containment measures. Until 60 to 70% of the population develops immunity either because of natural infection or because of vaccination, all the containment measures should continue.
Additional caveats are to be kept in mind while coming up with policies and strategies for effective population level vaccination. It is not clear whether those with evidence of prior infection, that is detectable antibodies against Covid-19 virus, have robust protection against reinfection and if yes, for how long. Recent studies have demonstrated that the antibody levels decrease rapidly in those with no or mild symptoms. The decrease in antibody levels, however, may not equate with a decrease in immune protection against reinfection. This is because the body harbors memory B cells and T cells. Memory B cells can be recruited to start antibody production at a short notice and T cells mount cell mediated immunity against the invading virus. Whether we need to test people for the presence of protective antibodies prior to vaccination is not clear yet.
Vaccination strategies will have to account for the differences in the various vaccines that are in the advanced stage of development. These are different type of vaccines, namely, mRNA, component proteins, viral vector, inactivated virus, and attenuated virus among others. This means there are differences in various factors such as temperature stability, dosage (single versus two doses), ability to induce both humoral (antibody-based) and cell-mediated immunity, the demonstrated duration for which they provide protection, safety profile, and cost among others.
Financing a massive vaccination program at a time when the country is going through great economic hardship is an important policy decision to be considered. Given the narrow fiscal space, policy makers must exercise priority setting. Any policy needs to ensure that the most vulnerable and the most essential people get equitable access to the vaccine without any financial hardships. There is a great risk of policies being influenced by the exigencies of political capital. These need to be curbed. Since health is a state subject, there should be consensus on formulating a national policy, for adoption by each and every State irrespective of their political dispensation.
It is hoped that the government is seized of the matter and is developing robust strategies involving experts across the various spectra of health systems. It requires greatest war-like operational planning in mission mode. India has the will to do it and it can.
Dr. Krishna Reddy Nallamalla
Country Director, ACCESS Health International