Vaccine efficacy wanes after three months, says Oxford study

The effect of Pfizer and Oxford-AstraZeneca (Covishield in India) vaccines on transmission of the Delta virus goes down three months after the second dose, says a research by the University of Oxford.

The study also shows that vaccines are definitely effective in reducing spread of the virus besides providing protection against the infection.

In fact, Oxford-AstraZeneca, sold by Serum Institute in India as Covishield, was found more effective than Pfizer. A vaccinated person is less likely to transmit either Alpha or Delta virus strain, though the Delta version “erodes some of the vaccine-associated protection against transmission”, stated the research, which was carried out in the UK in more than 1.39 lakh respondents. Researchers say this could be happening because the Delta variant spreads fast thus affecting more people in less period of time. The inferences drawn by the study may help understand the reasons why the Delta strain is more prevalent in countries where vaccine coverage is very high.

The University of Oxford study suggests booster vaccine doses to keep transmission under control.

AstraZeneca’s data on US clinical trials published recently too showed the vaccine demonstrated 74% efficacy at preventing symptomatic disease. The same for people above the age of 65 was 83.5%.

Also read: Covid-19 vaccine breaktrough infections — what we know and what we don’t

The Oxford University study said that vaccine definitely allows the viable infectious virus to pass out at a faster pace, but the ineffective viral particles left behind can still be detected during COVID tests, reported The Print.

Individuals vaccinated with Pfizer jab showed the lesser probability of spreading the Delta variant, compared to those who received the AstraZeneca-Oxford vaccine. The effects of both vaccines, however, start waning three months after the second dose. Even with its reducing effect, the vaccines provide sufficient protection against the Alpha variant of the coronavirus.

The effect of Covishield after three months of the second dose goes down significantly, so much so that the study found no difference in transmission of the Delta variant between vaccinated and unvaccinated individuals.