The Brazilian city of Manaus has witnessed so many COVID-19 infections that the local population may now be benefitting from "herd immunity", according to a preliminary study published on medRxiv.
The novel coronavirus pandemic has devastated Manaus city, situated in the Amazon rainforest.
Brazil reported 45.9 lakh COVID-19 cases as of September 24. This is the third-highest caseload in the world after the United States and India. Brazil has also reported 1.38 lakh fatalities related to COVID-19 – the second-highest death toll in the world.
The study suggests that the transmission of SARS-CoV-2, which causes COVID-19, spiked during March and April in Manaus before falling slowly between May and September.
Frequently Asked Questions
A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.
There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.
Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.
In June, one month after the outbreak peaked locally, 44 percent of the population was sero-positive for the virus. This number was adjusted to 52 percent after taking into account the false-negatives. This sero-prevalence rate fell in July and August due to waning of antibodies, the study suggests.
After data adjustment, the study estimates that the final epidemic size was 66 percent in terms of sero- prevalence.
While interventions by authorities and change in population behaviour may have helped limit the spread of COVID-19 in the city, the “unusually high infection rate suggests that herd immunity played a significant role in determining the size of the epidemic”, according to the study.
The fall in number of cases being reported on a daily bases has meant that businesses are reopening in Manaus faster than the rest of Brazil. Health experts, however, have cautioned that attempting to deliberately reach herd immunity is dangerous.Click here for Moneycontrol’s full coverage of the novel coronavirus pandemic