Astra response more with up to 10-month gap, 3rd dose: Study

Booster given six months after the 2nd dose beneficial, shows Oxford research

Immune responses to the Astrazeneca Covid-19 vaccine improve with a longer gap of about 10 months between doses, and a third shot can boost antibody levels even further, according to a study.

Extending the gap between the first and second doses increased the level of protective antibodies, according to research from the University of Oxford published Monday. The researchers were also able to show for the first time that a booster given more than six months after the second dose induced a strong response and increased activity against variants.

Many governments are grappling with vaccine shortages and questions such as whether to give booster shots to ensure hospitals aren’t overwhelmed this winter. The results may help countries determine whether to stretch their supplies by waiting to give second doses, while showing the way to improve protection — without completely redesigning vaccines — using a third dose. Most nations have recommended a gap of 4 weeks to 12 weeks between Astra vaccines currently.

“This is about preparedness,” Andrew Pollard, lead investigator on the Oxford vaccine trials, said at a press briefing Monday. This data show “we can boost responses giving another dose of the Astrazeneca-oxford vaccine and that’s really important.”

More research on the duration of immunity from two doses and protection against variants would help determine whether booster doses are really needed, Pollard said.

The study found that antibodies induced after a single dose survived to some extent after one year. Still, after 180 days the levels were half those seen at the 28-day peak. A second dose increased antibody levels between fourand 18-fold by one month after the shot, however. Volunteers in the latest study were drawn from Oxford’s original early and late-stage trials for the vaccine last year.

Immune response of Astra shot boosted by mixing dose schedule with Pfizer jab

A mixed schedule of vaccines where a shot of Pfizer's Covid-19 vaccine is given four weeks after a Astrazeneca shot will produce better immune responses than giving another dose of the Astrazeneca shot, the Oxford study said. In any combination, they produced high concentrations of antibodies against the coronavirus spike protein.

Pfizer, Moderna may offer lasting protection

The vaccines made by Pfizer-biontech and Moderna set off a persistent immune reaction in the body that may protect against the coronavirus for years, scientists reported on Monday. The findings add to growing evidence that most people immunized with the MRNA vaccines may not need boosters, so long as the virus and its variants do not evolve much beyond their current forms — which is not guaranteed.