A third booster shot is the most effective protection against Covid-19 for those to have taken two shots of Sinopharm, doctors said at Arab Health in Dubai.
Immunologists reported a ‘very strong’ response once a double dose of Sinopharm was topped up with a third booster shot of Pfizer BioNTech in offering protection against the virus.
Health authorities have taken steps to offer booster shots to those who have taken the Sinopharm vaccine.
Vulnerable citizens inoculated with Sinopharm in Bahrain have already been offered the US Pfizer booster shots following a surge in infections ad a tightening of restrictions.
In Abu Dhabi, the Department of Health is offering third shots of Sinopharm for those who had a second dose of the Chinese vaccine six months ago
Dr Gehad Eltayeb El Ghazali lead immunologist at Sheikh Khalifa Medical City, Abu Dhabi, said immunity begins to fall six months after a second dose of Sinopharm, but a third booster was safe and effective in tests.
“We have seen a very strong immune response when a third booster of Pfizer has been administered following two doses of Sinopharm,” he said.
“When there is natural infection from the virus, we see an immune response after about three weeks, and we see a similar response following a second vaccine dose.”
Research across the world is underway to see how effective mixing vaccines may be in offering greater protection against emerging new variants of Covid-19.
Stronger immunity in general may be offered against the virus, with research ongoing to assess exactly how effective heterologous prime boosting is.
A recent German study looked at research subjects receiving one dose of the Oxford-AstraZeneca vaccine followed eight weeks later by a Pfizer-BioNTech shot.
Blood samples showed that protection in individuals given two different vaccines was four times higher than in those who had just received two Pfizer shots.
Mixing vaccines could provide more options to health authorities to treating more vulnerable patients.
“From the beginning, we have observed variance in the immune response,” said Dr El Ghazali.
“Those patients with defective t-cells or some kind of anaemia have a worse response to the virus.”
T-cells aid the body’s production of antibodies to kill off cells infected by the virus.
Lymphopenia is a major feature of Covid-19 infection that damages t-cells, and other cells, and is more pronounced in severely ill patients.
Studies have shown the majority of people infected with Covid-19 develop a strong t-cell response, which bodes well for the potential for longer term immunity but that is far from certain.
“Given the nature of this virus there will be a SARS-CoV 3 and 4, we just hope it will not pose an existential threat to humans,” Professor Basel Al Ramadi, chairman of medical microbiology at UAE University in Al Ain.
“We only have a few vaccines now, but there are more than 280 under development.
“Most are injectable but a minority are taken orally.
“Ideally we want memory t-cells from these vaccines that can control the infection.”
A phase three trial of 1000 patients in the UAE who have taken the Sputnik V vaccine will assess the presence of antibodies and t-cells, four months after administration of the jab.
Prof Al Ramadi said asymptomatic or mild cases of the disease triggered a stronger t-cell response in patients when compared to those with moderate or severe symptoms.
A scarcity of t-cells were also found to be associated in older people and those with worse outcomes.
“Although we see antibodies in those who have had the virus, we still do not know how long they may last for,” said Prof Al Ramadi.
