The study results show that patients who received a single dose of Covishield after they had Covid-19 infection had 30 times higher antibody levels in comparison with those who received two jabs but were not infected. In the viral neutralization assay, those with hybrid immunity could neutralize the virus much better than those who have received two doses of vaccine or had prior infection alone.
It was also found that even a single dose of vaccine produces a very high level of immunity for a previously Covid-infected person. This high level of hybrid immunity (hybrid of natural infection with one dose of vaccine) is anticipated to last in the person’s body for a longer time, providing long lasting immunity.
“We found that in patients with AIRD, who had Covid-19 before, a single dose of the vaccine provided 10 to 50 fold higher humoral immunity than two doses of vaccine in infection naïve patients. This concept of hybrid immunity needs to be recognized. Those who develop hybrid immunity have such high levels of immunity and protection that they may not need a second dose or booster dose,” said lead investigator Dr Padmanabha Shenoy, who is also a clinical immunologist and rheumatologist.
To understand if a previously Covid-19-infected person develops hybrid immunity once vaccinated and how this hybrid immunity compares with vaccine immunity or natural immunity, a cohort study was conducted in 120 patients with autoimmune rheumatic diseases (AIRD) who had either Covid-19 or were vaccinated or both and had highest level of antibody. They were divided into four equal groups of 30 each the first group consisted of patients with AIRD who had taken single dose of the vaccine post- Covid-19 infection, second group had patients who had Covid infection in the past but had not taken vaccine, third group had patients who had single dose of vaccine but were not infected and the last group had patients who had double dose and were not infected yet.
Sera was collected from each patient approximately 30 days after the last vaccine dose or since the onset of Covid-19 symptoms (in the unvaccinated group). Antibodies to spike protein were estimated and virus neutralization potential of sera was tested. The ability to neutralize the virus was also studied through viral neutralization assays.
It was found that not just antibody titers, but this group of those infected who had single dose, had 100% seroconversion and neutralization was also the highest with 86.7% of sera showing more than 30% neutralization potential, indicating that a single dose of vaccine after Covid-19 natural infection provides better humoral immunity than two doses of a vaccine even in patients with AIRD.
“We recommend the central government to take this study into consideration while planning vaccination policies. Giving single dose instead of two doses to those already infected, may save close to 3 crore vaccine doses,” said Dr Sakir Ahmed, co-investigator, associate professor, Kalinga Institute of Medical Sciences (KIMS), Bhubaneswar.
“The major strength of this study is that we had collected sera and plasma at approximately the same time (30 days) post-vaccination and post-infection. The major limitation is that we have not looked at T cell immunogenicity. However, it has already been shown that peak neutralizing antibody titres correlates very well with the protection from Covid-19 infection probably independent of T cell responses,” added Dr Shenoy.