Should I receive the AstraZeneca booster shot at 8 weeks and not at 12? Here are the tests so you can decide


Prime Minister Scott Morrison appeared to have made a “captain’s call” yesterday for encourage people in outbreak areas of New South Wales to have their AstraZeneca booster closer to eight weeks after its initial firing instead of waiting for the generally recommended 12 weeks.

“We would be encouraging the second dose of eight to twelve weeks to be done earlier in this period. […]. This is consistent with […] and given the risks to people from the outbreak in this area, we believe it is important that they get this second dose of AstraZeneca as soon as possible. “

According to the official health advice from ATAGI, the Australian Technical Advisory Group on Immunization, most people receive the booster shot at 12 weeks for optimal protection against COVID, but in certain circumstances it can go down to four weeks. These circumstances include imminent travel or if there is a risk of exposure to COVID-19.

The concern of ATAGI and that of some other vaccine experts, is if you have a booster shot before 12 weeks, your body will not develop enough immunity to reliably protect it from serious illness.

Confused? This is what we know so far.

What is the official advice?

The evidence on which the 12 weeks recommended between the first and second features of AstraZeneca comes from a study published in The Lancet.

The study found that leaving less than six weeks between the initial shot and reinforcement gave 55.1% efficacy (protection against symptomatic disease). Leaving between 6 and 8 weeks between shots increased the effectiveness to 59.9% and, waiting for 9 to 11 weeks, the effectiveness was 63.7%. However, if the gap was 12 weeks or more, the efficiency jumped to 81.3%.

So to get the best protection from the AstraZeneca , you need at least 12 weeks between the first and second shot.

We now find an active outbreak of the highly transmissible Delta variant of SARS-CoV-2 in Sydney. Therefore, we must ask ourselves whether it is better to try to get the maximum level of protection or whether we should aim for a reasonable level of immunity as quickly as possible.

The Lancet newspaper did not include data on the Delta variant, as it was not widely circulated at the time, but this is fast becoming the dominant variant worldwide.

However, we know that two doses of the AstraZeneca vaccine protect against severe COVID-19 after infection with the Delta variant, while a dose no.

What tests are there for 8 weeks to protect yourself from Delta?

Morrison’s call for some people to have the AstraZeneca booster shot for eight weeks has not come out at all. It is an approach the UK has been using to advance the infectious variant of Delta, the same variant circulating in NSW.

We know that leaving less time between AstraZeneca shots generally reduces the effectiveness of the vaccine. But what about this in the context of the Delta variant? This is where things get a little complicated if we really want to calculate exactly how much reduction in vaccine effectiveness.

A study published in Nature a single dose of AstraZeneca vaccine induced essentially without neutralizing antibodies to the Delta virus was reported.

However, two doses induced a neutralizing antibody response in 95% of people, albeit at a significantly lower level than the Alpha variant (which originated in the UK).

However, there were neutralizing antibodies against Delta in the vast majority of people after two shots, antibodies that could mean the difference between a mild illness and hospitalization with a serious illness.

There are some limitations with this study. First, the efficacy of the vaccine was not directly evaluated (a clinical trial is required). Second, he used a range of intervals between the first and second shot, so we can’t say for sure the precise protection against the Delta strain at eight weeks versus the 12 weeks.

However, assessing the antibody capacity of vaccinated individuals to neutralize viruses in the laboratory is a good indicator of the quality of vaccine-induced protection, and this study highlighted the need for a booster shot to to protection against the Delta variant.

So with the number of infections in Sydney looking increasingly disastrous, along with the knowledge that one dose of vaccine is virtually useless against the Delta virus, it’s clear that two doses are put in the arms of as many people as possible. soon better. the strategy.

Two doses, even eight weeks apart, while not providing the highest level of protection possible, will still protect many of the serious illnesses.

What else should I think?

A reduction in immunity is not the only thing to consider when assessing the pros and cons of firing your AstraZeneca booster beforehand.

We just heard that there are more Pfizer shots on the way earlier than expected. If a Pfizer booster shot is made available to people who have already had two photos of AstraZeneca (and that’s very important), that could change the game.

In this case, and remember that this combination approach has not been officially sanctioned, it might not matter too much if a second early dose of the AstraZeneca vaccine gives you suboptimal immunity. Pfizer boost would boost your immunity.

However, it remains to be seen whether such a major policy change will occur in time to protect people who are currently locked up in NSW.

Takeaway message

The Delta variant is highly transmissible. So the weeks are important, and with Australia still heavily dependent on the AstraZeneca vaccine, for now it makes sense to reduce the time between the first and second time.

This is clearly preferable to staying unprotected for an additional month, especially if you are at higher risk for infection and / or serious illness.

AstraZeneca tests the reinforcement test against the COVID variant

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