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I have read many claims from (German) politicians COVID-19 vaccines only work for 6 to 9 month. It is being used to argue that vaccinations should be mandatory in Germany and Austria every 6 or 9 months.

A Nov 25, 2021 Zeit article [German] describes an EU proposal that would make EU-wide vaccination certificate last for only 9 months, unless additional booster vaccinations are given. (English article discussing the same proposals).

A May 15 2021 Frankfurter Rundschau quotes a couple of health experts as saying that the length of time the protection lasts before waning is unknown, but one assumes it will be around 6 months.

An August 27 NY Post article explains Dr ANthony Fauci and US President Biden discussed whether a booster shot should be required as early as 5 months or as late 8 months after the second shot.

What does the evidence show?

I think an answer should differentiate at least the following aspects:

Probability in dependence of time after first complete COVID-19 vaccination to:

  • transmit the virus to others
  • get ill with mild COVID symptoms
  • get ill with severe COVID symptoms
  • need to go to the intensive care unit because of COVID
  • to die because of COVID
  • to develop a serious "long COVID" syndrome

The aspects should also be differentiated between the available vaccines on the market and also differentiated per age group and underlying health conditions. One should also distinguish the virus variants.

For me it is at least conceivable that the aspects above are not strongly correlated, for example that the probability to transmit the virus to others may increase significantly after 6 or 9 month, but the probability for severe symptoms may not.

What does the evidence show? In particular if you want to decide if it is proportionate to make the vaccination mandatory every 6 or 9 month, I think you need a more differentiated picture about the date than only claiming that the vaccine "doesn't work" anymore after this or that timespan.

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  • Comments are not for extended discussion; this conversation has been moved to chat. Do not continue the discussion here.
    – Oddthinking
    Dec 1 '21 at 12:17
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    @Oddthinking: comments are for questioning why the OP is skeptical though. This is more like I'm too-lazy-to-even-read-the-articles-I've-linked-to kind of question.
    – Fizz
    Dec 2 '21 at 12:12
  • @Fizz The sources are all very vague on details, so the question seems justified to me. The first source is about a suggestion to expire vaccine certificates after 9 months, the second is about a politician assuming that immunity from vaccination might hold for around 6 month, and the third is about Biden and Fauci discussing plans to potentially require booster shots every 5 months instead of every 8. All provide different dates, neither sound entirely certain, and none list specific numbers on vaccine efficiency.
    – tim
    Dec 2 '21 at 13:20
  • Aside: The title of the question is easily interpreted as referring to the shelf life of an unspecified COVID-19 vaccine. The body of the question concerns the vagaries of the long term efficacy of a vaccination for an individual. Answers for either question would depend on which particular vaccine is being discussed.
    – HABO
    Dec 4 '21 at 22:50
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Six to nine months is a conservative estimate of how long antibody levels will remain high.

https://www.yalemedicine.org/news/how-long-will-coronavirus-vaccine-last is a good resource to look at for this. In particular, you should be aware that there are multiple kinds of protection:

The slow decline [in antibody levels] raises hopes that the mRNA vaccines will be protective for at least a year, if not longer

vs

last year, a study in Nature showed that people who were infected with severe acute respiratory syndrome (SARS), a different coronavirus outbreak that killed almost 800 people in 2003, maintained T-cell immunity 17 years after they recovered.

Being vaccinated induces both T-cell immunity and high antibody levels. High antibody levels can prevent you from getting sick at all. T-cell immunity will not prevent you from getting sick, but makes it easier for your body to fight off an infection. T-cell immunity is expected to last longer than antibody immunity:

"We need to do follow-up studies to confirm the longevity of the T-cell response to vaccination, but our results here support the idea that that response can be long-lasting," Wherry said.

In summary, you are unlikely to get sick at all for at least six to nine months, but even after that (unsure exactly how long because it's harder to study) the vaccine will still make it easier for your body to fight off an infection.

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  • That seems overly optimistic compared to the numbers I read (eg here). I think the article might be a bit out of date, considering that it is originally from May 2021 and also specifically says that "It should be noted that the trial occurred prior to Delta becoming the predominant virus variant" regarding the quoted "at least a year" number.
    – tim
    Dec 1 '21 at 21:00
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    You don't kill all the plasma cells from an immune response even if the antibody levels drop (and the antibody levels need to drop or after 20 years on god's green earth your blood would be a solid block of antibodies from every time you got inoculated with something). You can expand plasma cells if you see a virus a second time a lot faster than you mounted a full VDJ/maturation secondary immune response the first time.
    – CJR
    Dec 1 '21 at 21:18
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    @CJR: [citation-needed]
    – Oddthinking
    Dec 1 '21 at 23:23
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    Janeway's Immunology - Chapter 10 (Adaptive Immunity to Infection - The course of the adaptive response to infection)
    – CJR
    Dec 1 '21 at 23:44
  • @tim There are initial reports from Israel that immunity levels 5 months after the 3rd dose are higher than "right after" the second dose, so it seems the 3rd shot will probably grant at least 5+6 months of protection if the decrease in immunity is similar to what seen after the second dose.
    – Bakuriu
    Dec 10 '21 at 20:03
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The CDC recommends booster shots, starting at 6 months after vaccination for biontech/moderna (2 months for Johnson & Johnson).

Under "Data Supporting Need for a Booster Shot", they link to specific data (graph at page 14, data 15ff). Their source is Duration of effectiveness of vaccines against SARS-CoV-2 infection and COVID-19 disease: Results of a systematic review and meta-regression by Feikin et al. They show that:

VE against SARS-CoV-2 infection and symptomatic COVID-19 disease decreased approximately 20-30 percentage points during the six months after vaccination. [...] for severe COVID-19 disease, VE decreased by 8·0 (95% CI 3·6-15·2) and 9·7 percentage points (95% CI 5·9-14·7), respectively. The majority of VE estimates against severe disease remained over 70% for all time points.

There are also studies showing a more severe decline, eg Effectiveness of mRNA BNT162b2 COVID-19 vaccine up to 6 months in a large integrated health system in the USA: a retrospective cohort study:

Effectiveness against infections declined from 88% (95% CI 86–89) during the first month after full vaccination to 47% (43–51) after 5 months. [...] Vaccine effectiveness against hospital admissions for infections with the delta variant for all ages was high overall (93% [95% CI 84–96]) up to 6 months.

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