Booster shots necessary to keep severe Covid-19 symptoms, death at bay, says DDC
Two doses of a Covid-19 vaccine can boost the recipient’s immunity against the virus by 65 per cent and reduce the chance of developing severe symptoms or death by 88 per cent, the Department of Disease Control (DDC) said on Monday.
“Those who received two jabs and then a booster are 94 per cent less likely to contract the virus, and 98 per cent less likely to develop severe symptoms or die from the infection,” DDC expert Dr Thaweesub Sirapraphasiri said.
The DDC has been studying data from vaccine recipients and Covid-19 patients in Thailand from July to December 2021, when Delta was the dominant variant and had sparked a third and fourth wave of infections in the country.
The study also found that those who had received two jabs of the vaccine in July and August are likely to have their immunity against the virus drop to around 50 per cent by November or December. However, their immunity shot up to over 90 per cent after receiving a booster shot in November or December.
The DDC conducted another study in January 2022, when the highly transmissible Omicron became the dominant strain and began spreading across Thailand.
This study, which was only conducted in Chiang Mai, showed that people who had received three Covid-19 vaccines found their immunity against Omicron rise by 68 per cent on average. Also, there was no significant difference in efficacy among vaccines.
For instance, two jabs of Sinovac followed by an AstraZeneca booster increased the recipient’s immunity by 78 per cent.
Two Sinovac shots followed by a Pfizer booster gave recipients 63 per cent immunity. Two Sinopharm shots and a Pfizer booster increased immunity by 66 per cent. Two AstraZeneca shots and a Pfizer booster increased immunity by 62 per cent. A combo of Sinovac and AstraZeneca followed by AstraZeneca booster increased recipients’ immunity by 68 per cent.
All combinations still help reduce the chance of death from the virus by 96 per cent.
“These studies show that two doses of the vaccine are effective against Covid-19, but the efficacy will reduce after a few months,” Thaweesub said. “Therefore, people who have received their two shots should get a booster of any kind as that will help reduce the chance of them developing severe symptoms and death in case of infection.”
