Hybrid Covid immunity offers more cover than infection, says study

The study is based on an analysis of 11 other studies on the protective effectiveness of previous SARS-CoV-2 (Covid) infection and 15 studies on the protective effectiveness of hybrid immunity. “These results provide information that can be used to tailor guidance on the number and timing of SARS-CoV-2 vaccinations,” it says.

The study shows that hybrid immunity, coupled with primary vaccine doses, was effective in preventing severe disease and hospital admission in 97.4 per cent of participants upto 12 months.

The effectiveness of only hybrid immunity against re-infection stood at 41.8 per cent at 12 months. And, the effectiveness of only previous infection against severe disease and hospital admission was 74.6 per cent at 12 months.

After 12 months, the study says, protection against re-infection for all forms of immunity dipped to 24.7 per cent.

The study states that hybrid immunity with more vaccine doses provides more protection. Although examined in only one of the cohorts included in the analysis, the study also says that “hybrid immunity in combination with the first booster vaccination conferred a significant gain in protection compared to first booster vaccination alone” at 90 days.

According to the study, in places with high prevalence of infection and low resources, the focus should be on administering primary doses to people who are at the highest risk of developing severe disease. This, it says, will offer a high level of protection against severe disease for at least one year in people who have had the infection. India has administered two primary doses of vaccine to at least 90 per cent of people above the age of 12 years across the country.

The other key recommendation of the study is to roll out booster drives whenever an increase in number of infections is expected. “Given the waning protection for both infection-induced and vaccine-induced immunity… wider vaccination among populations could be timed for rollout before periods of expected increased incidence, such as the winter season,” the study says.
It also says that a six-month delay in booster dose “might be justified” in individuals with a known history of previous infection and full primary vaccination.

Asked about the study’s findings, Dr Anurag Agarwal, who is the former head of India’s Sars-CoV-2 genomic sequencing consortium, said “there is no consensus” yet on how frequently booster doses need to be administered.

“The necessary quality data to formulate such precise guidelines doesn’t exist to the best of my knowledge, definitely not for India,” said Agarwal, who is currently Dean of Biosciences and Health Research at the Trivedi School of Biosciences of Ashoka University.