By: Yvonne Atieno @MountKenyaTimes
Scientists from Oxford University now say delaying a second dose of the AstraZeneca/Oxford COVID-19 vaccine for longer than current practise leads to an enhanced immune response.
In a briefing to the Science Media Centre, Dr Teresa Lambe PhD, lead senior author, said that antibody levels were increased after a delayed second dose.
“a prolonged interval of 15 to 25 weeks, and even as long as 44 to 45 weeks between dose one and does two, you get a very strong antibody induction with these really long intervals,” said Dr Lambe.
Dr Lambe, an associate professor at the University of Oxford’s Jenner Institute, also reported an additional finding that in individuals fully vaccinated with the AstraZeneca/Oxford vaccine.
“When we gave them a third dose after about 30 weeks, we were able to augment the immunity – the antibody levels – and we were able to push them up to a level that we saw at the peak of the response after the second dose,” she said.
The study further found that a third dose given more than six months after the second dose leads to a substantial increase in antibodies and induces a strong immune response against SARS-CoV-2, including variants.
Studying the impact of a third vaccine dose, the researchers found that antibody concentrations increased significantly with a third dose; T-cell response and the immune response against variants were also boosted.
“It is not known if booster jabs will be needed due to waning immunity or to augment immunity against variants of concern. Here we show that a third dose of ChAdOx1 nCoV-19 vaccine is well tolerated and significantly boosts the antibody response. This is very encouraging news, if we find that a third dose is needed,” noted Dr Lambe.
Prof Sir Andrew Pollard, director of the Oxford Vaccine Group, said it was too early to say whether booster shots would be required in the autumn because there was currently a lack of real-world data about how long immunity lasted following vaccination.
However, “it is something where we need to keep looking at the data and make decisions as the months go by, about whether that protection that we have is lost,” said Prof Sir Andrew.
The study involved volunteers aged 18 to 55 who were enrolled in a phase 1/2 or phase 2/3 clinical trial of ChAdOx1 nCoV-19 and had received either a single dose or two doses of the vaccine.
Of the 90 participants who received a third dose, antibody titres were significantly higher when compared with the response 28 days after a second dose.
Side effects of the vaccine itself were also found to be well-tolerated, with lower incidents of side effects after second and third doses than after first doses.
Oxford University however says further research is required to follow up with study participants who received third doses beyond the period that was part of the initial study.
The latest development comes amid concerns of COVID-19 vaccine supply shortages in a number of countries including Kenya.
Kenya like any other country has been unable to get enough stock to administer the second dose, a situation that has forced the Health Ministry to pause the administering of first doses.
The majority of Kenyans have been inoculated using the AstraZeneca dose which is available through vaccine sharing platform, COVAX.
Specifically, there have been heightened worries about compromised immunity as the interval between first and second dose extended due to limited vaccine availability.
Typical intervals between first and second doses for the Oxford-AstraZeneca vaccine around the world vary between 4 and 12 weeks.
Dr. Willis Akhwale, the Chair, Vaccine Taskforce welcomed the news however noted that shot vaccinations will be easier to deploy in developing countries like Kenya.
“The findings are good, but it will be more important if we seek answers as at what point after the first dose do the antibodies wane off completely? Single shot vaccinations will be easier to deploy in developing countries since they will require less operational costs,” said Dr. Akhwale.
According to data from the health ministry, 1,003,204 Kenyans received their first dose of the Oxford-AstraZeneca vaccine.
As at Monday, 289,800 people had received their second jab, with the largest percentage being men at 56 per cent.
Data from the Health Ministry shows 68,688 healthcare workers have taken their second dose while the number of teachers stands at 36,167.
The number of security officers who have received their second dose is 21,781, 84,855 are people aged above 58 years while 78,309 are members of the general public.
CS Kagwe led health ministry earlier said plans are underway to procure Johnson and Johnson and Pfizer vaccines to boost the vaccination campaign in the country.