Although regulators in the United States have held fast to the requirement that people receive two doses of the Pfizer-BioNTech vaccine three weeks apart, the British government decided to prioritize giving as many people as possible an initial dose, allowing delays of up to 12 weeks before the second dose. The Israeli study could bolster arguments for emulating that approach in other countries.
Published in The Lancet on Thursday and drawing from a group of 9,100 Israeli health care workers, the study showed that Pfizer’s vaccine was 85 percent effective 15 to 28 days after receiving the first dose. Pfizer and BioNTech’s late-stage clinical trials, which enrolled 44,000 people, showed that the vaccine was 95 percent effective if two doses were given three weeks apart.
Katie Thomas
Another study being passed around as proof that regulators should delay the second vaccine dose to offer more people partial protection, because a single dose is supposedly enough. I have quickly skimmed through the study, but there are obviously several issues with this conclusion:
- the number of participants is fairly low, some 5 times lower than the large scale clinical trials used to evaluate vaccine effectiveness. Moreover, the participants were not selected to cover a wide range of ages and social groups, making the results inconclusive. This is basically the same issue that delays the authorization of AstraZeneca’s vaccine in the US and has led many countries to recommend against its use above a certain age.
- the delay analyzed here is small. The official recommendation for the Pfizer vaccine is an interval of three weeks between doses, so the study only looked at a delay of an extra week, compared to the UK protocol that allows for up to another 8 weeks of delay. This tells us nothing about what might happen to the immune response after these four weeks.
- also, most of the participants have already received the second dose, following Israel’s procedure, so there is no room for follow-up studies to determine at which rate the immune response might decline over time.
To me, the results seem completely in line with the trial results and offer no new insight. It is reasonable to expect that an immune response from the first dose will not suddenly vanish three weeks later if you fail to receive the second dose precisely on schedule, but I see no proof that it would remain at a high level for months without the booster shot.
Quite the contrary: Of the 170 HCWs who became infected, 89 (52%) were unvaccinated, 78 (46%) tested positive after the first dose, and three (2%) tested positive after the second dose.
This particular quote seems to support the opposite conclusion, since the number of infected people is similar between the ‘unvaccinated’ and ‘after first dose’ groups, but significantly lower after the second dose.
Dr. Anthony S. Fauci, the nation’s leading expert on infectious diseases and an adviser to President Biden, said at a White House news conference on the pandemic on Friday that the results of the study are not significant enough to change the U.S. recommendations.
He pointed out that the people in the study were on the younger and healthier side and the researchers could not say how long the protection from one shot of the vaccine would last. He also said it was possible that a less-than-optimal dose might not kill the most powerful variants of the virus, theoretically allowing them to spread more quickly in the population.
More relevant studies to this question are starting to be released from UK and Scotland, covering much larger numbers of individuals. But, as far as I can tell, these results also refer to a short delay – the Scotland study names an interval of 28-34 days after the first dose (presumably without the second), again not enough to draw the conclusion that a single dose is effective over a much longer period.
I continue to be dismayed by the lack of patience certain people display, and by their complete disregard for medical procedures. Just as some groups were desperate to end lockdowns and return to social life despite the risks, others are relentlessly advocating untested methods that could make things worse in the long run.
Fortunately there are more positive news as well: Pfizer recently announced that their vaccine can be stored at standard freezer temperatures for up to two weeks, making it easier to distribute doses to medical centers without specialized refrigeration equipment. And a different Israeli study reinforced the idea that the vaccine is very effective at stopping viral transmission, not just symptoms.
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