Immunity is induced differently by natural infection and vaccination. Immunity broadly is of two types cell mediated immunity by T lymphocytes and specific antibodies against viral proteins mediated by B lymphocytes. It is easy to measure antibody levels and when present in the blood we call the person seropositive. Cell mediated immunity by killer T cells is more difficult to measure but play a crucial role in destroying the infected cells and T cells also stimulate B cells to produce antibodies. Since SARS2 virus causing Covid 19 infection is new we don’t have enough data about how long the immunity last after infection and after vaccination.
One study published in the journal Immunity of 5882 people who have recovered from Covid 19 infection, found that antibodies were still present in people’s blood 5-7 months after infection. People who had severe disease had more antibodies than with those with mild infection. All of the vaccines approved so far produce strong antibody response. A study in the journal Lancet found that Astra Zeneca vaccine ( CoviShield in India)induced high antibodies with minimal waning ( reduction) for 3 months . Another study evaluated the difference in peak antibody levels among 172 people over 80 who received the Pfizer vaccine. There was 3.5 times more antibodies when they received booster dose after 12 weeks.
Vaccination can sharpen immunity in people who had been previously infected with Covid 19 and recovered. A letter published in the journal Lancet discussed an experiment in which 51 health workers in London were given a single dose of Pfizer vaccine. Half the health workers had previously recovered from Covid 19 and they experienced more than 140 times antibodies than pre vaccination levels. It is those who had mild or asymptomatic infection get the maximum benefit from vaccination. Hence people who had Covid 19 infection should receive vaccination.
Professor Eleanor Riley of Immunity and Infectious diseases Centre , University of Edinburgh, UK says’ immune response after vaccination is much more homogenous and show both T cell and B cell immunity. T cells and B cells have a central role in fighting of infection and crucially in establishing long term immunity.
Data upto 4 August 2021 from Imperial college London’s React study found that , compared with unvaccinated people those received two doses of vaccine were half as likely compared to unvaccinated to test positive for Covid-19. Public Health England data to date are consistent with the estimate that despite drop in efficacy against the delta variant compared to the alpha variant first detected in the UK,, vaccines used in the UK reduce the risk of death by 85% regardless of the variant.
All the vaccines currently used in India are safe. All vaccines reduce the incidence of symptomatic illness and death. They also reduce the risk of getting infected and thereby prevent transmission from asymptomatic carriers to vulnerable people who have high mortality from infection. Allowing infection to spread in community help to develop herd immunity, but this strategy cause an unacceptable rate of death and chronic illness like long Covid. Healthy individuals who get mild infection don’t benefit from vaccination, but they pose a danger to the elderly and vulnerable people. The Government has a duty of care to protect the life of all its people even at the cost of limiting the freedom of unvaccinated people. The best way to get immunity is not by allowing to get infected but by vaccination with minimal loss of life and minimal risk to vaccinated people.