Delayed second Covid-19 vaccine dose may help immune response - study

A delay in getting the second dose of the AstraZeneca vaccine heightens the immune response to Covid-19, a study has shown.

The Oxford University study shows that a longer delay of up to 45 weeks (11 months) between the first and the second dose leads to an enhanced immune response after the second dose.

The results released in a preprint on Monday suggest that with the vaccine supply shortages in most African countries, the extension of the waiting period due to limited vaccine availability is good for most Kenyans.

Supply delays prompted the government to revise the waiting period for the second dose from eight to 12 weeks but many have surpassed the stipulated timeline.

Sir Andrew Pollard, professor of paediatric infection and immunity and lead investigator of the Oxford University trial of the vaccine, says that in cases of a third dose of the same vaccine, it should be given six months after the second dose.

This, he said, leads to a substantial increase in antibodies and induces a strong boost to the immune response against the virus including the emerging variants in many countries.

“A long interval between first and second doses does not compromise the immune response after a late second dose, and a third dose of the vaccine continues to boost antibodies against the virus,” Prof Polland said.

The results were released as thousands of Kenyans are worried about delays in getting the second dose and that their immune system may be compromised.

Enhanced immune response

When examining the effects of a delay of up to 45 weeks between first and second doses in the study participants, results demonstrated that antibody levels were increased after a delayed second dose.

Additionally, the findings demonstrated that a longer delay may be beneficial, resulting in an increased antibody and enhanced immune response after the second dose.

“This should come as reassuring news to countries with lower supplies of the vaccine, who may be concerned about delays in providing second doses to their populations. There is an excellent response to a second dose, even after a 10-month delay from the first,” Prof Polland said.

The study also found that the vaccine's side effects were well-tolerated, with lower incidents of side effects after the second than after first doses.

Further research is required to follow up with study participants who received third doses beyond the period that was part of the initial study.

Data on protection from one dose after 12 weeks is limited, but Covid-19 antibodies have been found in the body up to six months after one dose. The full course provided with a 12-week interval gives 81 per cent protection for an extended period.

Dr Willis Akhwale, chair of the vaccine task force, assured Kenyans that their immunity will not be compromised given the delay in the timing of the vaccine.

Adequate immunity

“We are all going to be vaccinated, regardless of the time. No immunity can be compromised with a delayed vaccination, instead, a jab in the hand is better than none,” Dr Akhwale said.

Acting Health Director-General Patrick Amoth said that it is better for the vaccine to be taken however late it may take than failing to take it completely.

“We are struggling the get the few that we can. If you get the chance to have the vaccine even if the 12 weeks have passed, go and take the vaccine. There is nothing that your immunity will be compromised,” he said.

“We have had cases that some children delay to be vaccinated because of unpreventable reasons, but still when they get the vaccine they are protected. Go for the vaccine.”

Dr Ahmed Kalebi, chief consultant pathologist, on the other hand, advised the Ministry of Health to conduct a serological test at the point of administering the first dose of the vaccine to determine those with past infection.

He said for those who have been infected in the past, there is no need of giving them a second dose and that a single dose can give them adequate immunity.

“There is no point in giving people who have had prior Covid-19 two doses of the vaccine when only one dose provided can offer adequate immunity. All we need to do is conduct free serological testing prior to vaccination to save many doses and allow vaccine redistribution globally,” he said.

Surging coronavirus cases

Most Africa countries depend on the Covax scheme to get Covid-19 vaccines supplied by the Serum Institute of India.

India is the world’s largest vaccine producer, but the nation is running out of supplies to make life-saving doses for its own people and this has affected several counties including Kenya. 

India cancelled exports of vaccines as it grapples with surging coronavirus cases and falls behind on its vaccination targets.

In Kenya, about 1,005,901 have received their first dose of the AstraZeneca vaccine, with only 328,848 Kenyans getting fully vaccinated as of Friday last week.

The country began vaccinating its population in March after getting 1.2 million doses of AstraZeneca vaccines from India.

With the shortage of the vaccine, many countries are now asking for donations from wealthier countries and countries on the continent with extra doses to share.

Kenya has received 72,000 doses from South Sudan with an additional 358,000 doses of the same vaccine from Denmark to boost its second round.